TUBE BIAS, socket to me!

https://www.pinoydvd.com/index.php?topic=139769.0

OP check this thread out pretty good, pics in all...

Regards

I’ll say this and let it go.. It’s better to stay out of trouble than get out of trouble... Bias is part of maintenance. Very simple.

There are three types of bias adj.

1. The way the factory says to BAIS and WHEN..

2. The way others tell you to or not.

OR

3. NOT at ALL...

The correct answer is what the factory says... Plane and simple.

Yes it changes the sound.. especially if you bais low, it will sound muddy. If you bias HOT the amp will distort sooner (tube break up), and burn valves quicker... Bias is very important...

Bias hot and turn the volume up...LOL.. go ahead... Bias low LISTEN.. muddy as all heck. Especially 60-1500hz.. muddy. YUK...

jjss49, we are on the same page, 4 times a year is good for me.. YUP..

ALWAYS with a valve change..... ALWAYS....

<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>

Billwojo... I just got my New Maxi. It does 4 large valves at a time.
The Mini has been on back order for over 6 months.. They should have started shipping the 15th. There were 16 or 18 before me.. I love um.. A LOT faster a lot more accurate, than the older ones..  My 533 and 39 are OLD... They WORK very well, the 533 for small valves, and 539 for small or large valves.  I use them to compare... I use a couple of known test valves. Pretty good information...

<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>

Last but most important.. OP I’m glad your happy... What else counts..

NOW if your looking for a little nugget..... :-) It may change nothing...

One way to find out..

Regards

@elliottbnewcombjr

yes a wooden or plastic stick with a screwdriver blade at the end of it would insulate you from any spurious shocks for sure... that is why audio research supplies the skinny long plastic screw driver for bias adjustment -- here is one you can just buy quick from amazon

https://www.amazon.com/Potentiometer-Tools-Hardware-ADJUST-TOOL/dp/B06Y6FTGNT/ref=pd_bxgy_img_2/139-...

you probably know this but a proper bias setting is specific to a particular set of power tubes (it is not to the amp, irrespective of tubes)... change power tubes in the same amp, you need to re-bias... i have had different tube sets (even of the same make/type of tube - say a sovtek 6550c quad) need quite different bias settings to achieve the correct biasing level

question -- you use a wooden or plastic handled screwdriver as per above, cool - but how are you going to measure the correct bias level for each kt88 pair? i did not see instructions for your a88 amp how/where to measure it...

@oregonpapa

dunno if your ref75 is your first arc tube amp -- they made power tube biasing much easier on that amp (long overdue)... on earlier models you needed to open top cover, use multimeter with hook prongs clip onto both sides of a bias resistor and read 65 ma at proper bias level... reaching into the running amp with hot tubes with the clips or with the biasing screwdriver took some nerve and fine motor skills lol

here is the process for the vt100 -- point is, you need a way of reading the correct bias setting!!

https://www.youtube.com/watch?v=GnBuI0sLhcg

^^^ My ARC REF-75 is biased from the front of the amp through little holes. ARC supplies a long plastic rod with a screwdriver tip for the purpose of biasing. Works just fine.

Frank

How about I make myself a long wooden stick/screwdriver instead of plastic. Wood safe?

Well now,

I like the KT88’s more than the 6550’s, difference was obvious, as obvious as switching from Triod mode to preferrable ultra-linear mode.

I assumed all the difference was entirely in the tubes.

Seller told me he had it’s bias adjusted just a few months prior.

Now I’m thinking, it is possible seller had it biased for KT88’s, kept them, put factory 6550’s in, shipped to me.

IOW, I just got lucky, and the bias was part of the improvement.

What are the benefits of proper settings (every 6 months) and what are the potential problems if simply ignored, (as I have done for 47 years)?

If the adjusters are simply set in the middle of their rotation, as I always do, and the thing sounds great, should I risk electrocution?

i would say that if the bias is well set at the start (when new quad of kt88’s are installed) then over time as the tubes age the bias will run a bit low for ideal sound but if you can’t hear a difference, then leave it be... the tubes will become under biased as they age and they will run cooler/easier and actually last marginally longer in use - once again, if you cannot sense a sonic penalty then leave well enough alone, just enjoy the music

middle of rotation on bias pots don’t mean much, as there are different sensitivities in the pots and more importantly different bias needs of the tubes set being driven... so best to have a tech read the correct bias voltage for your tubes set and set properly once, then go from there...

as an audio research tube amp user for years i have become kinda OCD on bias settings as there is much lore about failing power tubes and how bias resistors can be damaged in the amps when a power tube fails - so i am conditioned to check bias conditions fairly frequently (once a quarter, say) - but to be honest i have never let the bias run way off under or over the recommended setting, and so i cannot speak to whether the sonic penalty is noticeable... if anything i set the bias 5-10% below the recommended level to get a little more tube life, and i feel there is no sonic penalty i could hear with various arc amps running 6550/kt88's -- vt50, vt60, vt100, ref 75, ref 110 etc etc...

Elliot, I am not quite sure I understand your question, "Sonically, what are your experiences?"  Do I think biasing an output tube makes a difference?  That goes without saying; a power tube cannot operate without some chosen parameters: plate voltage, plate and/or cathode resistor values, grid bias, etc, that determine the electronic envelope in which the tube operates.  For every tube, there is a data sheet, usually available on-line and/or in published tube manuals.  These data show maxima and minima for plate voltage, bias, plate current, etc.  The tube has to be set up so its operation falls within these upper and lower limits.  And taken with the plate curves I mentioned earlier, you can "see" how different choices within that envelope of values will affect performance when the tube is fed an audio (AC) signal that will have a voltage swing.  I use exclusively Atma-sphere OTL power amplifiers, so of course no output transformer, and the power tubes are triodes.  In fact, in 45 years, I have never owned a transformer coupled tube amp, only OTLs driving ESL speakers. With Ralph's help, I built my amplifiers so I can set bias current for each of the output tubes separately.  This allows me to "match" the tubes for the way they are treated by the circuit.  But tubes themselves are unavoidably at least slightly heterogeneous in the way they individually respond to signal voltage.

If you consult with tube gurus, many of them have their own pet theories on where to set bias points for various power tubes, for best SQ and/or for most power, longest life, etc.  (Sometimes the settings for best SQ conflict with maximizing tube life.) By the way, the description of vacuum tube operation in my previous post is for triodes only.  So called because there are 3 nodes, plate, cathode, and grid.  Hence a "tri"-ode, the simplest type of audio tube.  Most power output tubes especially on transformer coupled tube amps, will be tetrodes or pentodes.  The extra nodes are additional grids that can further control the flow of electrons to the anode, but only the one grid receives the signal (with some very rare exceptions; for example some Berning amplifiers drive the screen grid); normally the one or two screen grids do some of the modulating of electron flow by virtue of the voltage supplied to them.  Small signal input tubes and phono and linestage tubes are nearly always triodes.

thanks for providing that understanding, big help just knowing 'why' bias exists.

Is it fair to say, if it sounds great, don't mess with it, or why bother as some suggest?

Thanks and yes, if it ain't broke don't fix it. 

Technically, the bias setting really does make a difference. In practice however it is like an oil change, you will always swear it makes the car run better. 

By the way, the same concept of bias is used in tape recording. The little particles in the layer we want to magnetize to record on, they don't respond very well if all we do is feed them the audio frequency signal. They are kinda slow when asked to change from zero state. But if we excite them with a bias current, in this case 60kHz or higher, this puts them in a state where they respond much better to the music signal. Very similar or analogous to tube bias.  

Mine one time somehow got way out of spec, something like 2 or 3 times what it should be, and so I was anticipating this nice improvement after spending the few minutes to lug out the meter, get down on the floor twiddling and testing to dial them all in nice and perfect. And then... nuttin. Nada. Oh well. At least the car runs better now.

Bill discovered this, near me, it's Toyland to him

Greenbrook Electronics, filled with vintage as well as new stuff!

https://www.greenbrookelectronics.com/

I'll be standing on an AstroTurf rug I have at my workbench, nearly 2" thick plastic and rubber, concrete below.

OFF; no inputs; multi tester connections; ON; 20 min warm up; long plastic tool. OFF, disconnect.

Speakers connected?

Elliott, if it has those tiny little pots they make adjusting tools for that. I always called them "tweakers" LOL, Radio Shack sold a set of 3 for just a couple of bucks, made of plastic.
If your going to do this, just make sure that the power is off when you attach your insulated clip leads. Use your meter set to DCV and check the PS caps to see how long it takes them to bleed down. Most PS have a bleeder resistor across the caps that will discharge the high voltage in just a few minutes.
Not a bad idea making an insulated tool, easy to slip and make sparks/do damage.
I bet Greenwood has the proper tools, do I really need to give YOU an excuse to go over there? LOL.
BillWojo

How about a long carbon fiber tube screwdriver!!!

I'm gonna find something long enough n my shop, use my grinder to make a screwdriver tip, have at it.

tomic601

this mx110z is the best purchase I ever made, chosen based on this review

http://www.positive-feedback.com/Issue77/vintage_mcintosh_experience.htm

If it died, I would instantly buy another without considering anything else.  The mx110z has gone up in price a good bit since I bought mine 1-1/2 years ago.
.............................

this is just a long winded story now, nothing to do with bias.

The mx110z tuner: Richard Modafferi is quoted as saying something like "there is nothing I can do to improve it".

https://www.audioclassics.com/mods

I have a lot of respect for him, I met him once, very friendly.

I bought his JSE Infinite Slope Model II speakers when he was in business making them himself. They had his two patents. Joseph Audio still uses his infinite slope crossover in a few models.

The most accurate speakers I ever owned, the only ones I ever wanted after going to many NYC audio shows. Instantly wanted them! I got lucky, my friend Phil at Leonard Radio, ground floor of my building on 44th street (former Hammond Organ Showroom) knew I loved them.

He told me senior salesman Ray had taken in a pair on trade with burnt tweeters for $700. (new $5k a pair then). Phil and I ganged up on Ray, reminded him I had given them some good advice when they were planning their renovation (I'm an Interior Designer, more like Interior Architect, specialized in Corporate Headquarters).

Ray says "I'm gonna replace those tweeters and sell them for a lot of money! I said, no, I'm gonna replace those tweeters and keep em. Phil pushed him, he finally agreed. I rolled those suckers out, up the elevator, hid them in the AC room in case he changed his mind, got em home that weekend.

Now, what the heck to do with the big boys downstairs? I say to Donna, the attic is too hot/cold; the crawl space too damp; they wont fit through your mothers cellar door. Donna says, "what about the bedroom, I love those speakers". OMG, I love you!!!

Those JSE's instantly took over Harvey's on 45th street. Until they didn't.

I don't know this personally, and still have utmost respect for Richard Modafferi. My friend Wayne, who sold a lot of them, told me JSE's mistake was making the enclosures himself, he could not keep delivery schedules, delays so bad, wealthy customers mad, Harvey's dropped them. 

After years of them, using McIntosh SS MC2250, I decided to give the JSE's to my son and go back to tube amps, the Fisher 80z's and the big boys I use currently. Still using McIntosh SS C28 Preamp. Back to LP, I was not happy with C28's phono, I actually preferred the one built into the AT120TT I had. Had McIntosh Factory check/restore it, still preferred the AT120.

I decided to get a tube preamp, researched, found the mx110z which includes a tube tuner. Existing Carver Tuner was terrific but the mx110z tuner just sounds so involving. Carver Tuner is now in my office with the Carver Cube. I got both from Harvey's used shelf. Wayne called me when he knew a trade in piece was coming out of the service dept.

mx110z Phono: Wonderful, I can't imagine even thinking something might sound better.

bdp24

thanks for the reference, I'll search for his name, his recommendations.

Any personal experiences?

lewm

thanks for taking the time to respond with all that information.

Sonically, what are your experiences?

jjss49

I should have answered you earlier,

A88T, original version (they don't call it mk1).

It has internal bias adjusters, and it is the only version that has 4/8/16 ohm taps for my 16 ohm speakers.

Newer versions eliminated the 16 ohm tap, and added convenient and safe external bias meter and adjuster.

millercarbon

thanks for providing that understanding, big help just knowing 'why' bias exists.

Is it fair to say, if it sounds great, don't mess with it, or why bother as some suggest?

As for 'right or wrong', 'better or worse' how do you know unless you have a problem, or a problem/change presents itself?

Up to now, those same 47 years, my friends and I: any and all of my tube stuff has always been preferable to SS (darn good SS) with 'middle of the adjuster' settings.

twoleftears

Thanks, that is the factory manual which I have, no mention of bias at all.

I found a discussion from audiogon member plangco, says ,4; he uses .35 for longer life and warmer sound.

It is his "the voltages can be lethal" that gives me late life cowardice.

That, and the very old but unforgettable memory of being kicked on my assss by a tv I had just unplugged. I replaced the cheap internal speaker with a better external one. That's when I realized, there has always been the potential of better sound out of TV signals.

Everyone,

Thanks for the help as always,

I know how to do it, what the proper setting is.

These Cayins have high quality ceramic tube sockets, they are very tight. They are surprisingly beautifully made with high quality components, far beyond my old experiences of 'made in China'. I highly recommend them.

It sounds great, I don’t have any issue, except I changed from 6550’s to KT88’s, I thought, it’s time to learn. Electrocution warnings are the only thing holding me back.

........................

I don’t care about heat or tube life.

My questions were:

What are the benefits of proper settings (every 6 months) and what are the potential problems if simply ignored, (as I have done for 47 years)?

If the adjusters are simply set in the middle of their rotation, as I always do, and the thing sounds great, should I risk electrocution?

OK yours is older.. Still no biggie.. I was taught by an OLD guy in the 70s.
I looked at a newer one..

You can looked up the pin out on the valve.  Find the ground, find the plate, you could see the wire going to the bias pot.

There are a lot of the older ones with internal bias pots..

If you don't feel confident, best to watch someone do it. Pretty easy though..

Regards

that sino made a88 amp has been out there for years, sold under various brands subbrands (line mag, cayin, grant fidelity yaqin etc etc) and with different front panels and biasing features (or lack thereof) as the chinese manufacturer matured and tried to move up market and sell effectively into different overseas markets

elliott if yours doesn’t have meters or accessible biasing pots you are best off getting it in the hands of a tech who knows tube gear...

Strange.  No mention of adjustment here.
https://elusivedisc.com/content/pdfs/CAYIAA88T.pdf

https://forums.stevehoffman.tv/threads/tube-integrated-with-autobias-equivalent-to-cayin-a88t.784890...

if you haven't seen this elliott - some interesting background and discussions

Thanks Bill,

I've been asking this because I knew that, thanks for sending me the instructions.

Working inside, plugged in, serious warnings: You know I love to do it myself, but not this, at least not until I see it done by someone who lives to explain what not to touch!

Steve at VAS will do it while I wait/watch, so I'll schedule something when you and I can get together to go there.

Elliott, it may still be autobias unless you found out otherwise. A tube amp that has autobias has no test points or meters, like my MC40 monoblocks. But, just because it has none of those doesn’t mean it has autobias. Most older tube amps didn’t have that stuff, required you to get in there and measure. No chance you have a schematic?
Can you contact the company and get some info?................................................                                             On Edit: I searched and found biasing instructions and emailed them to Elliott. It is not autobiasing.

BillWojo

@oldhvymec, the old Hickok testers and the like tested MUTUAL CONDUCTANCE at low voltages, not at the operating voltages that they were likely to see. Makes a huge difference.
Would you pressure test a gas cylinder that routinely is filled with hydrogen at 2000 lbs by checking it with only 500lbs of pressure? Of course not, wouldn't even dream of it.
So why would you test a vacuum tube that runs at 450 VDC plate voltage with 100VDC or less. Sure, it can tell you that the tube is conducting but not how well it will conduct under a real load. That's best left to either testing in the actual amplifier or a modern tube tester like a Amplitrex AT1000 that can put up to 500VDC and 160 milliamps on the plates. There is another modern tube tester that sells in kit form that can test to much higher voltages as well. Both of these testers tie into a laptop computer and can plot curves for the tube under test. THAT's the kind of tester that can match tubes, not the older ones. Neither is cheap, I'd love to have one myself.
Not saying that the older tube testers are worthless by any means, they can be used for testing shorts (very important), gassy tubes and microphonics along with a doing life checks and basic health. But to match up tubes? NOT. That is best done either with one of the advanced testers or in the amplifier itself and a test meter. Anyone telling you different is either ignorant or trying to get over you. The best tube sellers today are using the latest test gear, the old TV7 type tube testers were the shitt years ago but old tech today. Times have changed my friend and this new tube testing technology is awesome.

BillWojo

My Cayin is A88T version 1, which has 16 ohm taps for my 16 ohm speakers.

It has no external bias adjuster, no bias meter, and no switch for tube type.

Later versions drop 16 ohm tap, add external bias and bias meter.

So, it’s bottom off, multi-meter alligator clips, screw driver, ON, electrocution or success!

ya and Roger.  M ( rip genius ) spent man years.....wait for it....building MUCH better tube testers....

Elliott, your 110z is a treasure, enjoy it in good health

In his Music Reference section of the AudioCircle Forums, Roger Modjeski provided lots of info about tubes, including their biasing. Those writings are still available for viewing.

I suggest you buy an elementary treatise on how vacuum tubes operate, and then read it. In the accepted model for a vacuum tube, electrons are emitted from the cathode when it is heated. The cathode accumulates electrons and hence is thought of as having a negative charge. Because the anode is positively charged, or relatively deficient in electrons, they flow cathode to anode. If this is all that happened then vacuum tubes would be like light bulbs; the cathode would give up electrons in an uncontrolled manner, and they would flow to the anode. When this process reaches a state of equilibrium, the tube would be burned out and that would be the end of it. But instead there is a "grid". The grid is situated in the path of the electrons on their way to the anode. In a functioning tube, most of the time, the grid carries a net negative charge with respect to the cathode, and thus retards the rate at which electrons get all the way to the anode. That is, when no music signal is present, the grid has a DC voltage on it that is negative with respect to the DC voltage on the cathode. When a music signal is present, think of that as an AC voltage, a voltage that varies with frequency and in magnitude and represents music. So, music enters via the grid which always has a constant DC bias voltage on it, in simplest terms. The music signal modulates the grid bias voltage, and in another story, that’s how we get amplification of the signal across a resistor that connects the anode to the PS voltage. When amplifiers talk about "bias", they are usually referring to this steady state DC voltage on the grid. That grid bias voltage also results in a steady state current (electrons) passing from cathode to anode when there is no music signal. This DC current is referred to as "bias current". The grid bias voltage, the "plate resistance" of the tube, and the power supply voltage between anode and cathode, also called the "plate voltage" together determine the bias current. (Ohm’s Law.) For any power tube, or any tube at all, you can usually find a complex graph depicting "plate curves". This single graph will show current on the Y axis and plate voltage on the X axis, and a set of curves depicting what that tube will do at different acceptable grid bias voltages for different changes in plate voltage or current. And....

what model cayin, elliott?

Don’t rely on your tube tester to match tubes ..

<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>

What would you test them with, or rely on?

A TUBE TESTER.... That’s right.. you have to maintain them too. LOL

I guess you need a tester for the tube tester?

Don’t rely on a "TUBE TESTER" to test tubes.. Just hit my funny bone..:-) One poster said.. "Monkey Bone"...

Oh and flip the switch back to normal position on your amp after the Bias check and set... New valves recheck a couple of times over the next couple weeks of playing... Keep an eye out for valve failure.. they do.. New more so..

Regards

Elliott, check the paperwork that came with your Cayin and see if it states that it has "automatic biasing" or something to that effect. If not, there should be a procedure on how to do it. Are there any test points on the top or back of the chassis?
If it must be adjusted and the measurements are internal flip the amp on it's back and use the spring loaded hook type test leads with the power off. Make sure there is a load (speakers) on the outputs unless stated otherwise. You want nothing connected on the inputs. They should have a setting (usually in millivolts) that you adjust a pot to. That will set the current flowing through the tube. Some amps have an individual pot for each tube and some share a pot between both tubes in a push pull type amp. If I recall, yours is a push pull design.
I suspect that it's auto biasing or more than likely you would have red plated a tube if your swapping tubes. Uneven current matching on the tubes can lead to a runaway current situation that results in red plating.
Don't rely on your tube tester to match tubes, they don't test the current at full operating voltages.
There is a Fisher forum on AK, lots of information over there on adjusting those amps.

BillWojo

MC conveniently forgot the 'more electric bill" part.

oldhvymec

no need to LOL about same gear forever, much of my setup is ’old vintage’.

The 47 years begin in 1973 when I inherited my uncle’s Fisher President II console. My OMG moment, the awareness of high quality sound. All components made in 1958 still work. It’s Fisher Mono Amps, 80Z: the transformers seem indestructible, I bought a spare on eBay just in case. I used original EL37’s, EL34’s, 5881’s I think, a 4th type I seem to remember. All legit substitutes, bias never adjusted.

Over the years, I found a few burnt resistors, replaced them. Had them checked by pros just because they are so old, a few innards replaced, nothing really.

They still are dead quiet (so quiet I left them on many times) and sound great, but for convenience I got the current Cayin A88T (1st and only Cayin), Liked it equally, and wanted to hear difference of it’s optional Triode/Ultra-Linear modes. And KT88’s for the first time. Goodbye Triode. Fishers ready if disaster strikes current gear.

The receivers: two Fisher 500C (1964 to ?) and Fisher 800C all sound great. 7591’s, perhaps I tried substitutes, I can’t remember. Bill has the 800C (500C with AM added) we traded for his Mitsubishi Vertical TT LV-5V.

Sherwood I gave to a friend who collects Sherwood’s.

Dynaco Preamp I sold, just because it was ugly IMO.

current McIntosh tube tuner/preamp mx110z (1962-1969), best purchase ever! Love it’s tuner and phono. Dead quiet up to 12 o’clock vol, I leave it at 10 o’clock, Cayin at 12 oclock, use my Chase Remote Line Controller for remote increased volume, and it’s automatic Fletcher Munson Loudness progressively engaged when lowered from it’s startup vol. level. (you need to find the correct interactive Chase/McIntosh/Cayin mix so normal listening starts at Chase factory start up level), many use it wrong and complain about it’s auto loudness, used properly it’s a great feature to retain involvement at low listening levels. I digress.

Current speakers are new custom enclosures with all the drivers from the Fisher console, all made in 1958. Re-coned the 15" woofers twice, once pro, once myself, gonna check em soon just to verify they are ok.

So, that’s all the stuff I never biased, the current issue is the internal bias controls of the Cayin.

What really counts? (personally I don't care about either heat or life, but would like to understand)

Heat?
Life?
Output stays Matched when adjusted?
Acoustic Performance?
_________?

First off, why do we do it at all? In very general layman's terms its to improve signal response and sound quality. Okay, but how?

What happens when we send a signal through a cold tube? Not much, right? Tube has to warm up first. Because a tube is a kind of valve that controls the flow of electrons we have to have some electrons to start with, of which there are damn few when its cold. 

But even after we warm it up we find every time we send a signal the first little bit that comes out isn't as good as later on. Like it has to go through warm-up all over again only this time on a very fine small scale. But the details in music are all very fine small scale so even this little bit matters.

What we do to solve this is keep the tube up in its optimal response zone by adding a small steady bias current. How small? There is no one answer. Its a judgment call, and a trade off. More bias, more current, more heat, more power, more wear, less tube life. In a nutshell.

The issue with balanced valves is just that "Balanced", left to right in volume and bottom to top, if it's a single, double, or triple.

Sometimes the left and right share the same valve, they need to be the same, bottom to top. Incorrect bias can cause the valve to distort to quick, (to high) or sound muddy and thin (to low).

If you're picky, and the amps are revealing enough, you'll hear the difference, no problem.. Gotta keep the pin pockets tight and clean and the unit tuned..

Regards

In each case the tube was in the +/- tolerance range for satisfactory operating performance?

I wish I find the article I read years ago about "tube matching" by an engineer who determined it’s baloney-at least for audio equipment. Maybe a rocket ship to Mars it may be critical

Let’s be honest-who hears a 1ma MM reading? Perhaps it shows on test equipment, but your ears? .

That said, I still do everything in an owners manual.

What type of gear? ALL Cayin? Do they need bias? What does the owners manual say? You've had the sames gear 47 years? LOL Just a couple questions..

IF it requires the bias to be set, it's usually not to difficult. Some units the setting are on the inside, that makes it a little tougher. BE SAFE...

Regards