Does anyone care to ask an amplifier designer a technical question? My door is open.

@unreceivedogma

 By “more power” I’m just going by where I set the volume control before and after. It was a surprise, as I thought there would be less, and I was pleased because in my layman’s view it meant less stress on the tubes and circuitry.

This is a popular thought, however where you set the volume control has nothing to do with power or stress on the tubes and circuitry. A volume control controls gain, not power. You an be at full power anywhere on the control setting depending on the gain of other parts of the system. 

Also, I’m not sure what you mean by better technology than cone speakers. First off, the Altec is a horn/cone hybrid. That aside, while electrostatics have their virtues, they don’t move air the way a cone does, as someone here also observed. That’s what I mean by the dynamic punch of the Altecs. I’ve heard some great horn speakers, with prices in the stratosphere.

The Altecs were designed to get a lot of SPL with not a lot of power. When they were designed 20 watts was a lot of power, now its not. I have not heard any good horn speakers, though one of my students has the Avantgarde 3 way. We are having a demo this coming week. Horn speakers tend to have peaks in the response. They are very efficient, however I am not running a movie theater.

Actually ESls couple better to the are and are virtually massless. A cone speaker is a "mass loaded driver" whose motion is totally controlled by the mass. The problem with mass, as we well know is how to start and stop it. 

Rather than defend cone speakers, lets open our thoughts to why they are so popular and do they belong in the home? Fine for cars and portable radios, but that is not HiFi.

There was a time when the best and most expensive speakers were ESLs. But then came along Wilson and the world changed. We made a $4,000 ESL with DD amplifier at Beveridge when wilson was still working in his garage. He won, we lost. What happened?

@bdp24 

Thanks for the compliment and notes on the RM-200.

I was also introduced to the Tympani speakers in 1973-4. At the time this product could only be bought from ARC dealers and was essentially a speaker that Jim made for Bill. Both were just starting out. At the time the largest amp ARC made was 75 watts/ch. Bill also required you buy his electronic crossover for the 3 way system which was a total of 8 panels. Those were the days. Great sound at nothing like today's high prices. Marketing took a back seat to engineering not its the other way round.

@shkong

I really like the sound of SET over PP.You can see my audio history in the below link.https://forum.audiogon.com/discussions/the-most-musical-sound-in-my-40-year-s-audio-historyThanks again for your kind advice

SE amps are often great with sensitive speakers. The 805 tube is an interesting transmitting tube. These types of tubes often exhibit low distortion over their entire power range. It takes power to drive them hense the 300 B is actually doing some work here. We used a 300B in a single ended amp to drive an 833 output tube. The 833 is a monster of a tube, requiring 10 volts at 10 amps of very clean DC for the heater. That part was quite challenging. I think we went for 100 watts of audio power, all transformer coupled. 

@unrecievedogma

I think the debate between cone and electrostatic is reminding me of the great cable interconnect debate. Could it be that this is just personal preference? Or even that my ears are just trained and accustomed to whatever cones do to the ears? I’ve listened to my share of electrostatics. Some were very impressive. Some were better than my Altecs in many respects. But none moved me.

All debates with audiophiles come down to personal preference. If you like your system then great. My friend Bruce DePlama used to say. "You go to Roger's house you hear Roger's sound. You come to my house you hear my sound".

The Altecs are loved by many. Nothing wrong with them. No one is overcharging you for them. They are efficient and work well with smaller tube amps. 

I would hope we all agree that speaker differences, speaker/amplifier interactions, are far more obvious than cables.

I hope we all have decent systems, without un-intended peaks, without horrible distortion, without noise. If you have one of those problems lets fix it.

@fleschler   

Funny that the latest ARC amps I've heard sound greyish, muted dynamics, etc. My friend has an ARC 75 which is no match for his Classic 60s or my voltage regulated amps. Worse, his amps, Ref 5 preamp and $10K CD player all have had significant break-downs after only a year or two. Yuk!

That is how I would expect the ARC amps to sound given their measurements. Sometimes there is a correlation. I see we still have reliabiity issues. I feel for ARC and the many people who work there. When Bill was selling the company he had 10 requirements of the buyer. One was to not move the company. Bill did some nice work, however he left a few things undone. He never made a short circit protected power supply. That makes techs and the owners who pay them really unhappy.  He had a thirst for new products which resulted in many mods because the first releases were unfinished designs. When a preamp goes from SP-6 all the way to SP-6E thats a lot of mods.

My question remains, I'd like to know what you opinion is of the VAC IQ (continuous autobias) amplifiers. They sounded great wherever I heard them and they appear to be conventional designs well executed. They must have good impedance outputs to make them adaptable to drive many types of speakers like your own amps.

VAC seems to be doing some good work these days. I have worked on one of their big preamps, it was nice but picked up hum from a power amp 2 feet away. We were surprised. 

Autobias can be done many ways. The problem with many autobias schemes is that they shift bias in the wrong direction when the music gets loud (above the class A region). If Kevin worked it out well Kudos to him. I still prefer a bias pot and meter. My bias is so stable as to be checked only a few times a year. 

However many  are looking at amps that dont need adjustment as my newer RM-10. We have found that many of the new tube generation do not like the though of having to use a meter and adjust something.

I am very happy that I put the LEDs in the RM-9 in 1985.The bias circuit lended itself to them and balancing the DC coupled driver was important. When I did the RM-200 bias LEDs were a complicated option due to the circuit and the driver needed no balancing.

I feel in some ways I'm punished for putting a supermatched pair of transistors at the input and thus entered the "Hybrid" land. As always I choose the parts to do the job best. A tube in the input would have gone back to Driver Balancing pots, CMRR pots, tube selection. Sometimes doing an audiophile a favor does one no good. 

Well, at least "Mikey likes it"

Im not going to go too far with the preamp vs power amp ease of design controversy. Everyone is parroting back the party line, which I disagree with. 

I did a shootout for phono stages for our local audio society. It was a strict A/B. We had several name preamps all the way up to $20,000. I will never do this again for a club. They were sad that only one of 8 preamps sounded really different and that one is also well respected. However that one was +3 dB at 10 KHZ and it was obvious. They left shaking their heads because when they compare the same preamps one at a time they "think" they hear big differences. 

I pride myself in preamp power supplies, RIAA accuracy, lowest noise. The RM-5 is the lowest noise 6922 preamp new or old. I know this because the noise is at the limit of the tube itself, not the circuit. 

I think a lot of designers have problems with the power supplies, noise (tube rush) and hum. .These problems are not easy to solve. Perhaps that is the source of the comment. 

Ralph, I measured your preamp's RIAA and it was +4 db in the bass. That is not accurate EQ. My RIAA accuracy is +/- 0.2 dB.
. 
What interests me is how it came to be thought that preamps are harder. What designer is going around saying that? Im not.

@atmasphere  We get pretty high figures and we do it with a tube.... As a hint, look into 2-stage CCS circuits. You aren't going to get good numbers without a decent CCS, a resistor or a single-stage CCS won't hack it.

Of course i use good CCS, what concerns me is the variations in the gain of the two sections of the 6SN7. Since I have the M-60 on the bench I will measure that. What kind of numbers should I expect and at what frequency do you measure it?

I guess this really depends on what is meant by 'current' (since the word has become a charged term in audio)! 

Current is well defined by science. I didnt know there was a special audio definition.???

And a lot depends on the 6AS7 in question too- the GAs don't hold up; most American tubes have problems in our circuit as well since they really aren't intended for fixed bias operation. We prefer the Russian variant; they hold up the best of any we've seen.

The 6AS7 is a pass tube in a DC power supply. Heres a link, one has to scroll down a bit and read the application paragraph at the beginning. I dont think brand is going to make a lot of difference as they are all made for the same application as stated clearly here. . 
https://frank.pocnet.net/sheets/191/6/6AR11.pdf

Speaking of bias I note the M-60 offset, which is entirely based in bias stability or lack of. The offset wanders  +/- 100 mV at 0.5 to 5 second rate. Perhaps its all power line related, but nevertheless its quite easy to see on a scope. The DCR of a quad 57 is 0.5 ohms so there is considerable current if the offset gets large.

Having my hands on an M-60 for several weeks now has given me a better opinion of it than I had before. My customer does not want to be adjusting the offset all the time or at all. He has requested I design a servo. I now have the offset down to about 1/10 of the original.
 
Although we disagree on many things I do appreciate your Gentlemanly approach, unlike that other fellow who left us.

@tomic601 

first thanks for the input on Ralphs amp, speakers likely the dead ESL-63 I mentioned in another post. I am away from them but I am assuming with ago all the panels are toast, the limited fault tree look I have done so far indicates EHT power supply issues. I am away from them so do not know on panel color, will check that when home next. Thanks all for inputs on rebuilders.

The fault tree should have the panels at the top and EHT at the bottom.  The EHT power supplies are usually NOT the problem in the 63's. The problem is dried out contact cement. All the panels fail over time and temperature cycling is their worst enemy. My friends died in a hot room one summer day. There are many videos on YouTube that show how the glue lets loose and how to rebuild them. Its not for the faint of heart. It is indeed sad that the 57 panels last forever and the 63 panels have a very limited lifetime due to.... GLUE!

I am away from my toolbox also but I will get DMM peak voltages measured today, SPL at 1 M

fun, real data will set you free was our mantra at work for 30 years..

As I listened to the modified and unmodified OTLs the other day on the 57s (that story is told in an earlier post of 11/26), I had the 57 terminals hooked up to the scope. I was constantly monitoring voltage. Music is fun to watch and anyone can get a good scope on eBay for under $100 and learn to use it if nothing else to look at music, look for oscillations, look for offset drift  Its really not hard, really. I suppose I sould make a video. 

I could see certain things the amps were doing. It takes a lot of experience to see and hear music and correlate, but indeed I could see current clipping and hear the mud is produced. I could see bass peaks due to low damping (that took a oscillator or sweep CD). I could hear that the low damping amp produced a boomy one note bass while the one with 4x the damping produced actual bass tones.

Years ago in the Stereophile "As we see it" column the writer asked several people what they listen for. His daughter said she listens to the "beat". Someone else the tonality, someone else the separation of instruments, someone else the soundstage, yada yada yada. 

I think this is important for listeners to think about what they listen for when they judge a system. If his daughter puts on a recording where she likes the beat it might not reveal any of the other things. But she just wants the system that gives her the "beat" 

I particularly wanted to hear high level high frequencies where the low impedance of the 57 would tax the amplifier. If I had Miles Davis I would have used him, but I dont have Miles. I do have Bach organ works with trumpet enchmade. Thats even toughter. 
      https://en.wikipedia.org/wiki/En_chamade

I could see and hear the current clipping. More hear than see. But I also knew I was in the 3% and over distortion area of the amp and 12 dB of simple feedback made a big difference in the clairty of this organ stop. I had a brief experience of being mentored by an old German organ builder so I knew and was facinated how organs worked. This music was chosen precisely to provide an audible test. It was done with levels matched by pink noise and immediage A/B switching.

BTW the 57 has a dc resistance of 0.5 ohms. If an amp has even 50 mV of offset that is 100 mA of output current which is also similar to the bias of most SS amps so at idle either the top or bottom transistors are turned off. This is not good for the speaker or amp. The 57 was meant to be driven by an amp with an output transformer where there is never any offset.

This is the stuff I think people should know that is never talked about. If you doubt me go measure it for yourself.

@krelldreams

At your listening levels an RM-10 would do the job. I need to talk with my salesperson about arranging an in home demo.

The RM-10 now has a beautiful but expensive wood base which I would not like to have go back and forth.

The RM-10 is very light weight (15# i think) and thus can be shipped economically. What would you say to getting the amp in a simple base and if you decide to keep it buy the newer base or take a discount on the amp with the simple base?

@atmasphere Hey Ralph

Roger, I think if you revisit the above comments you will find them to be incorrect. An OTL has to be able to drive real world loudspeakers and so can produce the same currents at the output as any other amplifier. FWIW, the output tubes in most OTLs can easily blow a 10 amp fuse in certain situations without damage to the tubes.

I still find that OTLs at low impedance are current limited. As to 10 amps without damage. When I put a 6AS7 on the curver tracer and go just a bit above the peak rated cathode current I see flakes of cathode coating coming off like sparks from a sparkler at much less that one amp. WIth the grid being so close they can easily fall into the grid wire and POOF. Horizontal output tubes that Futterman and I use are specified for high peak current about 1 amp. 

I will measure the power of the M-60 at the impedances you suggest. What numbers should I find? At what level of distortion?  The amp is now working well with fresh tubes and all DC voltages confirmed to be in line. I have always liked the WIggins circuit and if I ever produce one it will be with transformer of course. 

@bdp24  The J’s midrange (provided by the available-separately Model 80) was great by itself (unusually transparent for a cone speaker)

Thanks for reminding me the model number of the 80. For others who dont know the 80 was a full range speaker, woofer and tweeter as I recall, doing its best at being a full range, small, economical speaker.  Fulton made good sounding stuff. I don't know how but I always assumed him to be a compentent engineer with great listening skills.

He told the monkey story with a totally straight face like, Hey this really happened. We bought his wire. 

It appears you have owned some fine equipment. Nothing like we are faced with today, which is mostly marketing, jewelry and auto body finishes.  oh and bad specs. 

@almarg Correspondingly, at my 12 foot listening distance I have measured peak SPLs on those recordings of close to 105 db, with the softest notes being in the vicinity of 50 db. I used a Radio Shack digital SPL meter for these measurements, set for C-weighting and fast response.

My speakers (Daedalus Ulysses) are rated at 97.5 db/1w/1m, and have a very flat impedance curve with a specified nominal impedance of 6 ohms. My 12 foot listening distance corresponds to 3.66 meters. Putting aside room effects for the moment I assume that SPL produced by a box-type dynamic speaker such as those falls off at 6 db per doubling of distance, which means an 11 db reduction going from 1 meter to 12 feet. I conservatively add in 3 db to reflect the presence of two speakers (as I understand it that figure will actually be closer to 6 db at my centered listening position when both speakers are producing similar signals), and I add in perhaps 3 db for “room gain.”

97.5 -11 + 3 + 3 = 92.5 db at the listening position for 1 watt per channel. Let’s call it 93 db.

I add in about 3 db of margin to the 105 db I want my amp/speaker combination to be able to produce at the listening position. So the required minimum amplifier power (into 6 ohms) is:

105 + 3 - 93 = 15 dbW (decibels above 1 watt)

15 dbW = 32 watts.

Thanks for your measurements and math. I think the math will leave most with their head swimming. Perhaps you could add some details to the steps so that others, less math inclined, might work things out. it is nice for people to know how different speakers fall off with distance. Perhaps you could write that up for us. :)

I ask for SPL both at listening position and 1 meter for two different purposes.

I want to get to know the listener and measuring at 1 meter leaves out all those other calculations. One just works off the 1 meter speaker spec and adds or subtracts. If one is 3 db higher than the speaker spec he is at 2 watts, 6 db is 4 watts, 10 db is 10 watts, 20 db is 100 watts.

@almarg  . I recently changed to a Pass XA25, which is specified as a class A amplifier rated at 25 wpc into 8 ohms and 50 wpc into 4 ohms. Per JA’s measurements, though, it is capable of 80 and 130 wpc into those impedances. I presume that most of that increase represents the amp’s capability after leaving class A, although per JA’s comments some of the increase apparently reflects differences in the distortion percentages the ratings and measurements are based on.

I have a different take on the reason for the power disparity... simply heat. The amp got hot at 1/3 specified power of 25 watts. At 1/3 of 80 is would have shut down. I think I saw a "more later" on that from JA, but cannot now find the quote. Perhaps you can. 

I think what Pass Labs did is a sensible way to get around the FTC power test procedure.  Perhaps 25 watts is the class A region however the amp does just fine out of class A and I cannot see anything in the distortion plots that concerns me when the amp leaves class A to AB. 

Too much has been made of Class A amplifiers. Most dont know what class A involves. You could call this amp a 25 watt class A amp though its really an 80 watt, high bias AB amp that just wants to get around the FTC rule.

@fsonicsmith   And while a solid state input stage may very well offer better measurements, where is the proof that it sounds better? At the end of the day, isn’t it indisputable that it is cheaper to produce and less complicated?

Are you saying a solid state input stage is not a good idea, or doesnt sound as good, or you would not buy an amp with one?

@fsonicsmith 

I believe as does Ralph evidently that it does no good to have a great preamp and a mediocre preamp.

would you like to fix this sentence? did you mean one of those to me power amp, not preamp? Look i know ive stirred you up, but you did ask about ARC.I really dont care if you are familiar with my preamps or not. You have a lot to say about something you have neither heard or know anything about.

Frankly, and here is a technical question for you too, your designs, particularly your RM100 appears awfully similar to those of Don Sachs.

I dont make an RM-100. You think this is anyting like I make? http://www.dsachsconsulting.com/CitationRestoration_html_files/7564.jpg

 You tried to put me down that I must be "new to audio" (I am not, been at it for 43 years since age 16) and yet I bet 99% of us who have similar time in this hobby are not familiar with your preamps

.
If you were reading Stereophile and other print magazines pre internet you would have read reviews of the RM-5, 9, 10, and 200. I have not had a large internet presence by choice. 

I have another one. And this is not meant to be a challenge despite your likely impression that it is. What is your scientific engineering basis for concluding that damping factor, adequate power, and low distortion are the most important performance criteria for an amp

I have already stated my basis for all those many times here. JA agrees with me, Peter Walker, Bill Jonhson and many others feel these are very important. Since you admit you only have 1% (100-99=1%)  of my engineering knowlege how can I explain it to you. You seem to think I have some magic fairy dust I can sprinkle and make you understand. I really can't and this is making me tired.

If you cant understand regulation (damping) then you cannot appreciate its value. Why do people without technical knowledge want to engage in a technical debate? All they can do is parrott back something they have heard.

There were warnings that this thread could go south if it did not remain Q and A. I appreciate that. I promise not to respond in any way in this thread again.

Thank you for leavning us be. I think you are the only one carrying us south.

@kellydreams   . I did try a passive preamp in the main system recently and did Not like how it made the system sound

Not knowing the passive and what is was driving, including cables I would say this: 

I have no problems with passives. If one thinks of it as the volume control on an integrated that is somewhat separated physically the question becomes: What is in the way? What might be loading the passive? Generally the problem is cable capacitance or output/input impedance problems  (I wont say mismatch). 

Heres the way I look at it. In an RM-10 the input is right to the grid of the tube. In a preamp its the same thing. Why should it sound any different?

People do like preamps for other reasons, many of which may be imaginary. I made lots of preamps. Of course you need one for phono.

Bill Johnson told me they sell twice as many preamps as power amps. Seems people like to play with preamps more. Some say because its the thing you touch. 

In my system i got tired of the cables from the pre to the crossover. I wanted something really simple.

Because the RM-3 crossover has two knobs for high and low output I decided I needed only one, the bass and so made the treb pot into a volume control. Reduces cables and connector problems.

Now I think the way to make a crossover is with several line inputs, volume and bass level. So simple. I adjust the volume and sub level (100 Hz and down) on most every CD.

If you care to share the specs on the passive, cables and power amp we might figure out what was happening?

@maplegrovemusic  Roger - What brand and model subwoofer do you use ?

Its of my own design. It is very smal,l less than 1/3 cu ft. Therefore its corner frequency is 100 Hz and falls off at 12dB/octave. In the crossover I EQ it up at 12dB/octave so it comes out flat. I can start the bottom EQ wherever I want. Typically 30 Hz. It could be 20 Hz, Works the same way. 

This may be hard to understand because its no longer a mass loaded driver. It is operating in the region where regular woofers do not.  It is now an air spring drive and I call it the "Air Spring Woofer". It is not longer working under mass load physics. It is working under spring physics.

The amp is any old SS 100+ watt amplifier. Currently a nothing special Denon. The woofer level control is on the crossover.

This solves a lot of problems with powered subs. Unless they have a remote (do they now?) it is difficult to adjust the level for different CDs, I find when the woofer control is right next to the volume why not trim it. I  use a range of about 3 db for myself but always bump it up depending on what I think the listener might like. Generally Im playing to a under 35 croud and they like how the bass sounds .. and more of it, sometimes I give them 6-10 dB more. The bass control is marked in dB so I know where I am. 

Plate amps have short life if played loud. The solder joints just fall apart from vibration. Some just have a short life!

In my system the only cable going to the woofer is a speaker cable, shamefully 16 ga lamp cord. The woofer is already well damped and above the range it plays. The amplifier sits on the rack with everything else.

Do you know that most people do not hook up subs properly? I can sympathize, to do it right takes miles of wire. You have to run the preamp to the woofer and back to the main amp which may be far from the woofer. Theres cable capacitance issues, potential noise pickup, grounding, and the incredible cost of premium long cables. I presume 4 meter cables cost heaps more than half meter.

In either case, if you dont use the crossover you do not get the benefit of taking the bass workload off the satellites. I bet 90% of the subs out there do not use the crossover for that and the reason audiophiles dont trust putting their sound through the XO and rightly so. The electronics in most subs is not great.

Why dont sub makers put the amp and xo into a nice chassis to put on your rack? If this is such a great idea why doesnt everyone do it?  Two good questions for sub makers :)

@iaelas The solder joints just fall apart from vibration.Interesting. My Force is still going strong after 15 years. Pre ROHS.Two good questions for sub makers :)Another is "Why provide such useless controls?" Many subs are clearly not designed to be integrated in any meaningful way.Anyone interested in the effort expended, visit http://ielogical.com/Audio/SubTerrBlues.phpMost 'non-ap' listeners comment on bass definition rather than quantity

ROHS may be the death of reliability. However people are getting used to short life, recycleable electronics. 

Yea the controls are pretty lame and hard to see the markings if any. 

My sub is designed to work with ESLs as I like ESLs and they present a challenge to blend. An ESL is a resistance (air not ohms) loaded driver My woofer in its tiny box is also resistance loaded (air spring)

@bdp24 

Yow, things are warming up around here ;-) . I like opinionated people, it requires and reveals passion. That’s true even if I see things differently; no two people agree on everything, and everyone develops their own priorities and tastes in music and it’s reproduction. I, not being an engineer, love reading about hi-fi design by those who are, and find discussions of design philosophy and styles very intellectually stimulating.

Like many Americans, on Thanksgiving day my assembled family expressed, member by member, what they are thankful for. I’m thankful for having Ralph, Roger, and all the passionate Audiogon music and hi-fi enthusiasts contributing to this forum!

Thanks for your kind words. I like strong opinions as long as they can be supported. So many audio "truths" are more rumors than truth. Who said what and when. I strive to quote members accurately, check spelling and grammar. (where is the spell check on this forum?)

Passion sometimes brings out the best and the worst in people. Somtimes an honest answer from someone skilled in the field is not appreciated. Sometimes no matter how well one can back up his point it is never taken. A lot of this would play miserably in a formal (Harvard style) debate.

Why do people who dont design preamps or even understand them want to say which is harder to design. Thats a very personal thing. I don't go around saying things like that. Each design, pre or power, is its own challenge. One picks his challenge and goes for it. I like to do things that have not been done before and I feel the few designs that I choose to produce and sell are my best work. Others are just studies. Thats the art part of it.

@fsonicsmith  Well, I lied. I have to respond. Ralph-I can't believe that you said that about me after I have done nothing on this Board (in multiple threads) but praise you and after you agreed that preamps are not easier to design (well) than amps. Yes, there were a couple typos in my last post due to being busy and typing in haste, but my points should have been clear. I could easily recite ten typos and misspellings in the various posts of Mr. Modjeski, were I to feel the need to resort to that.
It is also shocking to me that Mr. Modjeski criticized the hell out of your M-60's biasing circuit and claimed your RIAA curve in your preamp is not up to snuff and you are doing nothing but kissing his arse

.

hahahahahahahahahahaha.  Honestly this is my first reaction to reading whats above... Thank you, I had a difficult day setting up a strict A/B.  

@cakyol   I am also looking for a lab/bench symmetric power supply of up to +/- 100 volts DC at about 2 - 3 amps (so about 500 - 600 watts) and having a very difficult time finding it. The very rare ones I have seen are in excess of $1500. I need such a supply for testing purposes. I do not want to build one.

Does anyone know of one around a max of $500 ?

I would just buy two identical supplies, float the grounds and put them in series. Thats what I use on my bench.

You want a lot of watts, 1/2 KW. Most bench supplies are not up to that.  This company made great stuff. This is getting close. www.ebay.com/itm/POWER-DESIGNS-6050A-Variable-Universal-DC-Source-AS-IS-See-Description/292803892089...

Keep looking at ebay. What you want is rather unusual due to the amount of power, heatsinks to manage the drop across the transistors. At the power level you want a linear supply is unlikely. Almost has to be a switcher to manage the losses. Imagine if you are asking for just a few volts at 3 amps. The high side of the regulator has to be above 100 volts so 300 watts are dissipated in a linear regulator. Thats a lot of heat

What I would do is just make a brute force power supply and run it from a variac. Thats what I have done when I need that much power. Its nice, no losses, no heat. 

I do recall that HP made some very high power regulated supplies and handled the dissipation by tracking the regulator with the variac. Again, that is to reduce the heat dissipation. That would be a great and not too difficult project.

@atmasphere

Hi Ralph. Im curious if you use an inverse RIAA network to check your EQ. If so where did you get the values? I built mine from the advice of Peter Moncrieff, Mitch Cotter and Dick Sequerra who were the first to discover that many RIAA EQ curves were off. Of course I used precision parts.

Since then I have used my "box" to test dozens of preamps from as many manufacturers and found all of us to be in agreement within 1/2 dB except for the one we had at the SFAS phono pre shootout and yours.

@cakyol I am therefore using 1800 VA toroidal and a 270 amp rectifier. Caps are 4 x 47,000 uF but s I mentioned, at 85 degrees C the caps are rated at 2000 hours. Therefore they are the weakest links in the amp. I saw some Nichicons with 105 degrees C at 10000 hours but they were about $250 EACH (phew). The rectifier, altho likely to be used for welding applications, has soft switch characteristics AND it is quit fast, so would be suitable for audio.

Electrolytic cap life is much longer than the ratings. Im not sure why they are being so conservative. Perhaps thats all they want to guarantee. They all do it. I was surprised by it too when I first saw the short lifetime. My experience was that the life was much longer.  

I have nice nichcon caps in my RM-9s that ate 35 years old and just fine. They probably run at 150 F.. The thing that kills lytics is the loss of moisture over time. If the moisture stays in the caps go on forever.

So you dont need to spend $250 each. Those older caps on eBay will suit you fine, expecially if they are NOS. If one fails, no biggie since you know what to do. Please fuse accordingly with the lowest current slow blow that will get you past the inrush or come up with an inrush limiting device.

@tomic601    ......so these A/B
can describe some of the switch gear involved as a DIY project

In essence one takes one or more relays and switches a single speaker (or pair) from one amplifier to the other. That is simple. However the output levels, using pink noise, must be closely matched within 1/4 dB or better. It is well known that if one amp plays louder than the other the louder one will be preferred. Its a well known trick on how to sell the inferior product, just play it a little louder, but not enough to make the volume difference audible. 

To match levels you need a pot that switches also, or the pot need not switch if the amps are ok playing unloaded, which most are. 

What is hard to deal with is all the wires and little things like the long wire to the button, matching levels, checking and double checking everythings.

However this is how I evaluate my amp, my mods and other amps. I am starting to mod some popular amps that I feel I can improve. This is a new area of interest for me and I want to make sure I am not going backward. Therefore I leave one channel (or one mono) stock and compare it to my mod. 

One has to know what one is looking for and what kind of music at what level will expose the differences. I try as wide a range of music as any listener might himself. Only 1 of 10 CDs I find to be useful. Some are horribly compressed, some already muddy, some dont have the right kind of instruments. For instance a harpsichord is not going to reveal distortion, Its already full of harmonics. 

Perhaps here is a good place to modify my statement about the difficulty in designing amps vs preamps. Its not about the difficulty and I wonder who started that. Probably some self serving designer who doesnt know how to design a power amp. There are companies like that where their power amps do not exist or are just horrible.  I simply find power amps more interesting to design so my work has focused there. 

I think the RM-5 is one of the best full function 3 tube preamps out there. If I did it today, 37 years later, I would do it the same way. The RM-1 is lower distortion, wider bandwidth but a lot more complicated. I did not want to make 1,000 of something so complex, support it and deal with the people who buy the really expensive stuff. I wanted to make something that sounds good, works forever, is affordable and brings joy to the user. 

I have had the opportunity to work on many higher end preamps and they are difficult, they go through tubes at an alarming rate, cause the owners much frustration and cost in keeping them going. Sadly they often don't sound that great either. If the phono EQ is fudged thats a no no. 

@jdjohn   Any thoughts on kits like this modeled after the Dynaco ST-70?  http://www.tubes4hifi.com/bob.htm#ST70  This isn't a mod or upgrade for stock ST70s, but a kit for building a brand-new amp. Some of the design changes are listed under 'ST70 amplifier features' if you scroll down the page a bit.

Looks good. I like to see the 3 tube driver board. Do they have a schematic?

The original single  7199 tube driver was flawed by tube to tube variations. Some good 7199 would bias up in a region that actually produced a lot of distortion and reduced power. There are many 3 tube drivers. I would like to know more about theirs. 

The kit looks good and priced well. 

@tomic601  Also on the subject of heat.... this is NOTHING compared to creating a beast like the 787
stick to principles, there are different approaches to solving problems

i like the emerging theme from Eric ( Bdp24 ), Ralph and RM about early audio experiences, and especially mentors. I find that very useful and also a good mentor / mentee relationship benefits both.
for what it’s worth my mentor is Richard Vandersteen, a guy I greatly respect.
but can and certainly will learn from others.
great thread
jim

Thanks Jim, I liken this thread to conversations I had with my mentors. We talked about physics, acoustics, amplifier design all the way down to why I should put chokes in my RM-9  mkII. Bruce DePlama got me onto that one. 

Everyone was nice, no headbanging or harshness. We just shared information. We shared that we knew to be true from our own experience. DePalma also turned me on to the 100watt one pair EL-34 application. This application is always challenged when I bring it out. It is in the data sheets I went over in my Burning Amp presentation. http://berkeleyhifischool.com/having-fun-at-burning-amp-2018/

Anyone who does not believe you can get 100 watts out of ONE PAIR of EL-34s had better have a look. 

@teo_audio  

They left shaking their heads because when they compare the same preamps one at a time they "think" they hear big differences.

They do hear big differences at home. No doubt about it.

Long term listening does reveal bigger differences than short term listening of unfamiliar complex systems, rooms, etc.

Especially unstressed at home ---long term differences being notable -- with the entire home package being a familiar.

Anything else being paraded about....is well, horsepuckey of the most damaging kind.

Read up on listening tests and the human ear. It’s not a machine, it’s biological, and is individual and has learning curves, and these aspects take time. the ear is a living moving changing variable. and different in every single person. Seven billion different sets of hearing.

It even possesses intelligence and capacities levels like minds and IQ. Yet most people don’t mention these entirely obvious realities. Like your eyes, and mind, they come with a almost totally blank page, and you build it out from some very basic starter forms.. You learn your way to hearing, with your individual package that has as much variation in individuals as does IQ.

Bamboozling them with a test that no one can pass, without adequate amount of time spent in front of it, does not substitute for hearing knowledge and skill/

There was no bamboozling and nothing like the pseudoscience you propose on your website.  http://www.teoaudio.com/technical/

I ran into you on the cable threads. This thread is about answering questions. 

Please leave us alone. 

@krelldreams

What differentiates a passive “preamp” from a “tube buffer” with level and switching control? I really like the idea of a simple level control with switching capability, but as I stated earlier, my first try at using a passive, albeit a very inexpensive example, was less than stellar. Specifically, I’m looking at a Schiit Saga to try as a replacement for my tubed preamplifier. I’m weighing options for use with a tube amplifier, but I’d also like to understand what a tube buffer does differently than a tube preamp. Also, would the gain of a preamp “help” a lower powered amp sound more muscular, or is that more “made up” information?

A passive preamp has not active stage. A buffer is an active stage (tube or transistor) with unity gain. It has a high input impedance andlow output impedance which helps drive a long cable. However is the cabe is short and of low capacitance a buffer is not needed.

I dont know why this is blue, its just another problem with this sometime frustrating app.

Im sorry you had a disappointing adventure with the passive. Perhaps its specs would reveal why. Do you have some specs?

I looked at the Saga, Web page is hard to navigate and its all black.. Mike Moffatt has a good reputation, the product is likely ok , but the lack of any technica info is annoying. They are putting out a lot of product in a short time. That concerns me.

I did find the specs, you do know its a hybrid, thats odd for a buffer which is usually a cathode follower. The input impedance is rather low at 10K but most modern sources an handle it. If you are driving something easy then there is no need for the buffer. Im sure many will disagree.

If you have a good preamp, why change?

As to the muscle, No, that is made up, who is saying so?

I said I was done in this thread and once again, I lied. I swear this question is in good faith and not meant to challenge or make a point. While looking over at Tungsol's website I saw this;

Engineers and musicians have long debated the question of tube sound versus transistor sound. Conventional methods of frequency response, distortion, and noise measurement have always assumed linear (clean) operation of the test amplifier and have shown that no significant difference exists. In actual operation most amplifiers are often severely overloaded with signal transients. Under this condition there is a major difference in the harmonic distortion of tube and transistor circuits.

http://www.tungsol.com/html/faqs14.html

Please be aware that this paper was not written by any Tungsol engineers who are long gone as well as their factory and any tribal knowledge. 

This is the work of New Sensor who has taken over the name, probably with no resistance, and making the tubes in Russia. Im not saying these are bad tubes but they are not Tung Sol of America.  The KT series apperars to be good and I have tested the 120s and 150s. The data sheet for the 150 is in Tungsol style but not of Tung Sol quality. No plate curves, Gm seem too high. Not informative as in the good old days. I have offered to help them.

Also keep in mind that New Sensor sells to the guitar amp market by 100 to 1. Nothing wrong with that. Thanks to the guitar guys for keeping the demand for tubes going. We audio users are a drop in the bucket. 

@bifwynne  Btw, I owe you two quads of KT-150s for matching. The 3rd party vendor from whom I purchase the tubes didn't match the tubes to ARC spec.

Btw, I owe you two quads of KT-150s for matching. The 3rd party vendor from whom I purchase the tubes didn't match the tubes to ARC spec.

We have been awaiting your tubes. Time has passed and we have to get back on the same page as to the specs for current and G2 volts. Better not to wait on these things. Strike while the iron is hot as they say.

The difference between Bill Johnson amps and the current products is night and day. I appreciate the simplicity but not so much the performance specs. However specs arent everything. We are finding out some very interesting things on some listening tests. Very hard to get a really good handle on an amp without an A/B and a reference. 

@atmasphere  A choke is helpful as it can be used to help filter out the 60Hz sawtooth waveform that is part of the rectification process.

Ralph, Im sure you meant to say 120 Hz ripple, not 60 Hz unless you are using half wave power supplies.

Chokes are indeed great things and not found in many amplifiers these days because its just too much trouble for some designers to have them made. I put two in the RM-9 MK II as Ultralinear amps benefit from them greatly. The G2 on an ultralinear has the same ripple as the plate. Where a pentode amp can have additional filtering for the G2.

@andrew 

This has been a great and informative thread. Thank you for sharing your time, knowledge, and insight. I've learned a lot.

A question for you: any further thoughts on ARC's M300 monoblocks? They're a fairly...unique design and perhaps the best evidence of your view that WZJ's ARC designs were often over-complicated. That said, I enjoy them, and they've only blown up a couple times over the years. Any further comment?

(As to your point about the reliability of ARC products, I also have a pair of Ref 600s and pray every time I switch them on that they don't go up in flames.)

One other question: for those of us with super-inefficient speakers like Magnepans, what should we be looking for in an amplifier?

Look at this from Stereophile 

Peak Current (via 1 ohm, 2ms pulse)
8 ohm tap: +13.7A -13.5A
4 ohm tap: +16A
2 ohm tap: +18A
1 ohm tap: +24A
Read more at https://www.stereophile.com/content/audio-research-m300-monoblock-power-amplifier-measurements#8yHmL...
That is an impressive amount of current. The damping factor of 30 and 0.05 THD are impressive also. The full review is good reading. 

A continuing wonder of Audio Research's designs is how they can sound so good with such a complex signal path.
Read more at https://www.stereophile.com/tubepoweramps/585/index.html#REEwDyeIIFoMddwp.99

We can see that current ARC amps are no where close to what Bill achieved. One problem with complexity is fixing it. How bad did yours "blow up" 2 times?

If you can handle the the praying for no smoke and afford the rather short tube life then carry on. For those who cant I would go SS. 

There comes a point when tube amps just get too big. The alternative is get a high power tube amp with transmitting tubes. One pair of moderate sized transmitting tubes, like 833s,  can produce 300-1000 watts. Having a lot of smaller tubes in parallel is not so practical. One pair of 833s is about the same cost as one pair of KT 150s. or other KTs. And they look really cool. Id make you a pair if you wanted. Thats the big tube WAVAC Uses SE but I would go push pull. 

What is the re-tube cost on the 600?

@prof  So my question is: What exactly is happening to cause the type of sonic changes on hears when changing impedance settings for a cartridge?

My know-nothing layman’s hunch is that it’s similar to how speaker impedance interacts with certain tube amps, where some combinations contour the frequency response...and (sorry for the word) damping factor? (The changes in the bass in lower impedances do give me that "lower damping factor in the bass" vibe).

Good question. Cartridges are very different in how they respond to loading. My Denon 103 is a 14 ohm cartridge (as I recall) and likes 100 -200ohms load. More load drops signal level, dont ever go that far, and makes the sound rather dead. No load is rather bright. 

On the other hand the Lyra cartridges are so low in impedance that they dont respond to loading so we, in the SF audio society did some tests and found the Lyra best unloaded. 

There is not any relation to speakers and amps that I would care to make. A cartridge is a source, the load is a resistor. Not much else going on. 

@teo Some Ignorance is so manifold that it is used to commit to attacks so libelous and underhanded... that the person initiating is practically kicked off a given forum. So obvious to all, that there aren’t even words for it.And then that illiteracy and ignorance is paraded about as somehow being informed. That we can all be that dense. Jebus. What a horrific world that would be. So far gone that it can’t even be explained to a given person how far off base and wrongheaded a given comment might be.

I think im being called out but so poetically I can hardly be certain. I think Teo has a better future as Poet and Philosopher. 

His verse is  almost Shakespearian

  https://en.wikipedia.org/wiki/Sonnet_94

Bruce De Plama (Brians brother) often quoted the last of this. 

For sweetest things turn sourest by their deeds;
Lilies that fester smell far worse than weeds.

Here's a schematic of the ST-120 version (sans values for resistors and capacitors), which is apparently the same schematic as the ST-70 except for resistor sets.
https://drive.google.com/open?id=1IMaAaaWRuIU8v-_OZ3jfrcQCI5a0gpP8 

Nice circuit, simple. The 16 ohm tap is a bit silly and taking the feedback off it can have both good and bad effects. Otherwise, classic Marantz, Heath, Eico, etc.

@cardiff  Here is one nobody seems to have asked yet...

What is the role and importance of significantly upgraded power cords in component design? It seems to me that the PC is a fundamental part of the electronic device and that the manufacturer should optimize the cord for the device in building it. What are your thoughts on the matter as someone who actually builds electronics?

I put the proper cord on my RM-9 but now people want me to put an IEC on there so they can use theirs. I did opimize but thats not good enough for the PC and fuse people.  May I also offer that a captive cord has one less pair of connections. When you pull current on a IEC it gets hot, is that good?

Before audiophiles got into power cords most manufacturers went to IEC connectors for no other reason that it makes the amp easier to handle and pack up, not so people could go fooling around with wire. 

@mrdecibel Roger, this is a GREAT thread, thank you. I agree that all of the nasty comments and bickering should be kept out of this thread ( as well as all threads ). This thread is about learning, as I see it, and I am learning a great deal ( maybe understanding 1 % of it ) And yes, this thread has me thinking about trying tubes again in a power amp. : Going back to damping. In my early years, I owned several ss power amps, a few high powered. Two in particular, were an original Ampzilla, and a factory built Dynaco 400. Having many speakers at the time ( DQ10, AR 3, Klipsch Lascala, just to name a few ), the Dynaco had a bloated, slow, ill defined bass in comparison to the Ampzilla. Both were rated at 200 wpc into 8 ohms ( as I mentioned, these characteristic were also in all of the tube amps I had at the time ). Can you explain if these characteristics between the Amnpzilla and Dyna had anything to do with damping ? Thank you in advance. Enjoy ! MrD

.

Thanks, the nasty comments and bickering are charateristics of the people who make the comments. I ignore most of them. When I look at the threads they get on I can hardly imagine what sort of person they are. I am happy to have little of them here. I guess every forum has its trolls. 

At to your sonic observations. Ampzilla was and is a great amp. I think Jim B designed the Dynaco also, but I am unsure. If you find a schematic I can likely tell. People should know that some designers art is easy to spot, just as an artist’s paintings or sculptures. Bongo Jim, as we called him, was a really great amp designer, great pianist and all round fun guy. I have a picture of him Bacsom King, Mike and Laura Elliott at a BBQ at my home in Santa Barbara many years ago. Ill try to find and post it.

 Sounds like you have had some bass issues. Both SS amps should have good damping, I know Zilla did. Tube amps with poor damping = bloated bass and other problems. Would love for you to hear the listening test we have going on right now with two identical amps except that one has been modified to have 4x damping and 1/4 x distortion. The bass difference, clairty and air on the QUAD 57 are quite apparent. We are doing some serious listening with a very tight setup.

@pryso

That is a simple A-B is not adequate, even though you may find differences. I believe at a minimum you need to have A-B-A.

What exactly is A-B-A? we just go back an forth as desired. All connections are cleaned with De-oix from the start.

@ieales  I'd be curious if trained listeners can reliably detect the sound of the switcher

Trained listeners have found the switcher to be transparent. Sounds like in your current setup the listener does not know which he is hearing at the moment? We could certainly go to that. With the results we are getting the difference is easy to pick up on. 

@bifwynne  Not sure what you feel is deficient with the ARC Ref 150SE specs. If you care to elaborate, please do

Thanks for not getting at me since you own these amps. All I am saying is that Bill was on a mad quest for low distortion and high damping and achieved that in the one amp I called out for that. My only negative was its complexity. See if you can find that post. 

What I feel is deficient is exactly what JA thinks. Somtimes us folks do agree.  https://www.stereophile.com/content/audio-research-reference-150-power-amplifier-measurements. What interesting to me is that most audiophiles agree with each other by disagreeing with the technical people. It is still a mystery to me why people without technical knowledge want to disagree with technical people who are making this stuff (for better or worse). Sometimes I feel like im just fueling the fire.

JA does me a great favor when he tests an amp, then I dont have to. I have 400 pages of test notes on 200 amps and preamps that I have measured over the past 35 years. Testing an amp is a laborious task if you really want to get into whats going on. 

For you and everyone out there. There are things going on in certain combinations of amps and speakers that cannot be easily predicted. However these effects are rarely present in a good amp with good performance measurements. I have tricks that go beyond what JA does. For instance I put a 0.1 uf cap (similar to some speaker cables) across the output of a big Adcom amp while was on the bench and luckily connected to an AC Line amp meter. When i touched the cap against the output terminals the 10 amp meter pegged and i quickly disconnected the cap. I just holding it. Didnt get hot though 1200 watts was going somewhere and that somewhere was the transistors. 

I know some people have unknown Birdies going on in there system. Birdies are brief supersonic oscillations that occurr on specific parts of the wave at specific levels. If you drive a simple woofer directly that is the easiest way to see them and they sound like clipping but you are not clipping. 

I have personally, in my own store in the 1980s, watched a BIG Levinson ampifier smoke when connected to a high end speaker cable that had some parameter (perhaps capacitance) that the amp didnt like. It just sat there as little trails of smoke came out, and frankly I was amused.

I know im off topic but... motto is. Just because an amp passes the 2 uF load test (somewhat standard) does not mean it is stable into smaller capacitances that might be present in many cables. Whether you like lamp cord or not, It is the proper constructin for a speaker cable. Just not exotic enough for most. Hey man, its just wire.

Anyone else smoked and amp with a speaker cable? 

@whitestix  Roger,
I recall you saying at Burning Amp a year ago that you did not like 6SN7 tubes in preamps.  I have a preamp that uses these tubes and it is the best I have ever heard in my system.  What is the problem with these tubes from a designer's standpoint?  Thank you.

 Have a look at the most recent BA video where i discuss the tube. I point out where the mu starts falling off, its 5 or 10 ma. but have a look for yourself. Id like everybody to look at whatever suggestion applies to them. So look it up. 

As long as you can get ones that dont make noise or ring much when you tap them then you are ok. In my experience those are hard to find. Remember the 6SL7 was made for audio.The 6SN7 was made for black and white TV and was never, to my knowledge, used in the audio chain. When factories make a tube they pay attention mostly to the characterestics the tube was designed for, again not for audio, therefore they cared not about noise of microphonics. WIth 6SL7s they cared plenty. 

My guess is that people use 6SN7s simply because they have the right gain,  just by luck. BTW, the 6CG7. 6FQ7, 6GU7 was the 9 pin replacement for the 6SN7. Much easier to find. more modern construction. How do people like those?

YOU have to keep in mind the train has been a rolling for a long time on the 6SN7 for audio so it had a good hand on that tube for no reason technically. It also might be that this tube was just lying around everywhere with new old stock for days. People used to throw them away because after B&W televsion was replaced by color that tube was replaced  by the  6FQ7... right away. 

@lemonhaze Hi Roger,Am I glad I found this helpful thread. I have a Mark Levinson 23.5 amp that hums.The hum is loud and stays constant in amplitude regardless of the position of the volume control. I am driving it with an Aikido linestage that I built and which from driving various power amps I know to be quiet. I tried lifting the earth leg first on the line amp and then on the power amp but hum stubbornly remains.  I bought the amp used. I realise that it is quite ancient and probably needs to be re-capped. I took a look inside and it appears somewhat daunting.

Has anyone suggested putting shorting plugs into the inputs of the amp. That is the true test. If the amp hums through the speakers just as loudly then it off to the shop. Nothing is lower noise than shorting plugs :)

Quality amps, like yours can keep their caps for 40 years if it runs cool enough to keep your hand on continuously. Most re-capping is performed by the shotgun method. They just do them all rather than find out whats needed. Perhaps thats not bad, but many times caps arent even the problem and what they put in may not last as long. Re capping has become way overdone. 

@prof    Actually, the talk of switchers raises another question I'd like to direct to Robert:

I have more than one amp I like to use for my system. It's a minor pain to switch the cables, but it sure would be nice to have a switcher where I could switch between amplifiers to the main stereo speakers. (So interconnects would lead from one output of my preamp to my main amplifiers, and out the other output to a second amp. Depending on which amp I wanted to use I'd just flip a switch.

At one point I did a bit of research and saw some candidates, but for the most part they looked awfully cheap, which left me hesitant.

Would you say a fully transparent switcher of the type I'm describing could be built?

Yes we have one, can make you one with a volume control to balance the gain of the two amps so they play the same loudnes. They, God willing, you flip back and forth, on the same speaker please, and hear of not hear the differences between the two amps. This is exactly what we are doing.

Then you can invite your friends over and really have some fun. You will likely find what we have found.. Some amps sound very similar with differences too small to be sure they are real and some amps let you know pretty quickly what they are up to. We find good correlations with measurements.

What are your two amps.

@cardiffkook

Roger said....  I put the proper cord on my RM-9 but now people want me to put an IEC on there so they can use theirs. I did opimize but thats not good enough for the PC and fuse people. May I also offer that a captive cord has one less pair of connections

Cardiff said.
That is what I suspected you would say. I have tested expensive upgraded power cords in my system and never noticed any improvement or difference. I notice large differences between amps, preamps, cartridges, cartridge loading and even in minor changes of speaker toe in. But in my system, I have yet to hear any difference between pc's. I am not saying there are no differences, just that I haven’t heard any so far in my system, compared to the cord included by the manufacturer.

I think we need to hear more from the people like Cardiff who have tried powercords and not heard any difference. I will allow it because we have heard quite enough from the pro side, too much. Lets try to balance the issue. Lets give voice to those, like Cardiff, who can clearly dissern difference in his system.

Anyone who has bought a power cord and owns an SPL meter, or oscilloscope or any measurement equipment is welcome to report their findings. I have reported mine. 

Anyone who has spent over $100 on cables and has no SPL meter had better go get one. :)

@krelldreams   Roger asked for specs... the only spec I know of is “1.2k” hand written on the bottom of the case. This was only a test anyway since I’d need more than the single input this one provides. I was not aware that Music Reference made passive devices (?).

 I am considering both tubed and solid state phono preamps. Any design parameters that I should be paying attention to? Any designs to avoid? I currently only need one for a high-output MC cartridge (MM gain and loading), but I plan on trying other cartridges in time as well. I’m not opposed to getting a step up device if a cartridge I get in the future needs one.

BTW, i looked up the Axiom. If you have an ohm meter just connect it to the input jack and output jack and get some numbers. Non of them are good for long runs as we all know. If yours is 1.2 K ohms thats a rather low number unless the source is much lower. 

For  you preamp you need to focus on S/N ratio and RIAA accuracy and distortion which should be nill. If you find a measured review I will look at it. You want at east 60-70 dB signal to noise ratio at the output of YOUR cartridge. 

We might build a few phono preamps on special order. The one I have developed for Clio has is all tube start to finish, 3 gains, 12 loadings, tape EQ available (he likes 15 ips tape). It uses only 4 tubes which I am rather proud of as most will use more and give you more trouble. 

I tried a FET front end some years ago and just did not like it. A Low noise FET is about the same noise as a SLN 6922, so there is no noise advantage there. You can get the lowest noise with transformer inputs, but then you have to deal with placement issure and the sound of the transformers. 

For EVERYONE,

My new/old/previous technician Ben arrives today and I will be spending most of my time with him and not so much here. I will continue to answer valid questions. We will be making and posting videos at the Berkeley hi fi school site. http://berkeleyhifischool.com/ and on You Tube. Videos are what I want to spend my time on.

In the last week we have gotten off track. This thread is intended to answer questions and not to have people give opinions of my or others answers. I am always willing to debate a point that can be supported. That means supported from a recognized authority. For instance, concerning tube characteristics, ratings and applications that means data books from RCA, GE, Sylvania. Take your pick, they all agree with each other because RETMA made them. Did you know that all brands of tubes had exactly the same price lists? In otherwords you could carry a RCA price list in the 70s, as i did, and a 12AX7 was the same list price even if Telefuken made it. One list.

In some cases I have offered to build a A/B box for those interested in really hearing what is going on. It is my firm belief that is the most revealing way. Others may differ and continue to differ.

I thought the other day, Why not build a switch box with several IEC inlets and one standard outlet and a relay or switches. Let people listen to power cords on the fly. Two would be enough, or more doesn’t matter. Fuses too. What is wrong with that test? Lets do some real research.

I am not interested in de-bunking pseudoscience. Established science needs no de-bunking. To those who write up pages of pseudo science and create paradigms to make excuse for bad specs I no longer care to see here. Skilled people in this industry have come up with some minumum standards for noise, distortion and output impedance. I happen to agree with John Atkinson on these. Best wishes if you care to minimum standards. There are always outliers and they will be most adament.

One thing I have learned in this popular and intense thread it that many audiophiles have created a religion with various belief systems. I’m sorry but that interests me not at all. You can’t design a good ampifier on religious principles. You may get one to work, to make some music, but there will be much missing. Sorry.

I thank all for making this thread the most popular for two weeks on Agone. Im not leaving, just shifting my focus back to my real work.

Short questions without a lot of unnecessary information will get my first attention. Most questions can be asked in one or two sentences.

@bdp24 

@ramtubes, Roger, I know you consider the 6DJ8 superior to the 12AX7 for use in a phono stage, but let me ask you this anyway ;-) : how do you feel about substituting a pair of 5751’s in place of a phono amp’s 12AX7’s? I know the 5751 exhibits lower gain and noise (in the 1980’s I had a Dynaco PAS 2 that was "modified" by Frank Van Alstine, and he put in 5751’s. That pre was very quiet.), but are there trade-offs involved between the two tubes? Is the 5751 a true direct replacement for the 12AX7, regardless of application? Or are there circuit considerations? If used in an RIAA moving magnet phono stage (gain of 42dB or so), will the 5751 automatically provide a little more headroom/freedom from overload than the 12AX7?

The 5751 is slightly different froma 12AX7 and close enough to be tried. We have plenty of very low noise ones. CJ has used them for years. I use one in the integrated I am developing. I could have used a 12AX7 but like the 5751 better. it also happens to be a "Premium" tube which means they took more care on consistancy and long life. It falls under the "industrial" category where failures are not appreciated. Headroom is more of a circuit parameter than a tube parameter. 

@roberjerman   I have found more data on the 6N30 tube. Same pin-out as 6DJ8 and 6CG7. Plate dissipation 7 watts max. Plate voltage max at 250. Looks like the 6CG7/6FQ7 will work!

The Russians copied many of our tubes as did the Chinese. What you want to do next is compare Mu, Gm and Rp of the tubes at similar operating points. Let me know what you find out. Great question.
 
Low noise 6CG7s can be a little difficult to fine but I have found some.

@atmasphere   Roger, you might want to do some reading at the links I posted in my prior post. Most of this post (except perhaps the comments about subjective listening) is incorrect. As I pointed out earlier, the load is not for the cartridge's benefit- its about the preamp.

Please explain. Im all ears.

There's plenty of old school audio electronics that used the 6SN7. As you know, its geometry is similar to that of the 6CG7/12BH7 and 12AU7 (the latter being the same as the 12BH7 but with the entire structure sawed in half)

My dad built the WM-2 in 1956 so I am very aware of 6SN7, as was Heathikit who used them everywhere they could. Are you aware that most of their early products were built largely from WWII surplus of which there was tons. They would buy tons of surpus and then figure out what to do with it. 6SN7 were in great abundance. I think a 6SL7 might have made a better choice and I snuck one in a Williamson, changed a few resistors, and really liked it . Much more linear tube (low distortion). Why, because it was made for audio, not B&W television.

There are some great books on the history of Heath written my people who were there.  

This other stuff about sawing tubes in half make no sense. Ive taked to tube designers and they dont talk that way... at all.

As to it being lower in microphonics, the tone is of course different as the structure is different. But I would not say they are less microphonic than a modern 6922.  But this is just my experience of testing over twenty thousand 6922s

Here is the best data I found for the 6H30. The curves look right and the table of parameters done at different plate voltages and currents are very interesting. The first 3 columns are his set up values and the rest are the results. 

 http://www.triodeel.com/6h30.html

Is this like a 6FQ7?  Granted the pin out is the same.

After I get a few responses I will give mine. I want the questioners to do a little thinking on this one. Kinda like Homework.