Tube amps - what 3 things…

Tubes can be intimidating to start with all the different design approaches and care that is required for speaker matching. Once you start it can be addictive.

Excellent point Ralph!  Properly executed ultralinear topology is stunningly impressive.  When executed properly, it is another reason why fixed (manually adjustable) output tube bias is essential, in order that output can be optimized for ultralinear topology.

So many short cuts are available in tube (well actually any) amplifier design that it is impossible to find a commercially available one that doesn't employ any of them.  For example: does any manufacturer use an inductor filtered power supply instead of the much cheaper (and lighter) capacitance filtered power supply?  None that I know of.  The only way to get an absolutely uncompromised tube amplifier is to specifically requests such a build from a highly knowledgeable designer/builder, which will result in a very expensive and very heavy amplifier.  

I'll refrain from exclaiming how extraordinarily special the amps I use are other than to state that they are the result of such a request.

 

The ability to switch between modes (triode, ultralinear, pentode) is nice.

I do not agree with this statement. The problem is that to do this properly, the output transformer (and the rest of the output circuit) has to be set up to handle the different operating points, and in practice this rarely happens.

If this is a concern, FWIW the original patent for ultralinear operation showed that the result had the same linearity of a triode with about 90% of the efficiency of a pentode output section. A lot of manufacturers realized the benefit, but to avoid paying the company that held the patent, moved the screen taps of the transformer to a slightly different spot, resulting in less linearity and simply called it good, thus bypassing the patent.

That patent has long since expired and the company that held it is unknown to most audiophiles and transformer manufacturers. As a result, its rare that the correct location of the screen tap on the winding is ever used. But if it were, ultralinear would be the only way to go if you are using an output transformer. Any competent transformer manufacturer could work this out though. Tradition of using the wrong position on the winding is literally the only thing stopping them!

@atmasphere

Great synopsis 👍

My God all this is so incredibly complicated. 

And after saying that, commentary herein is awfully impressive.

The ability to switch between modes (triode, ultralinear, pentode) is nice.

A fish with wheels and wings would be nice too.

Get a great sounding amp, not an overly complex spagheti bowl.

+1 on P2P wiring with silicone or other high temperature, NOT PVC, insulation. Tube amps require service and good designs can be made great with component upgrades and cct tweaks. One of my favorite amps was a Citation II reworked in the mid 80s. IMO, it ate my AR studio amps for lunch.

@hilde45 My experience as well. My PrimaLuna has been EXACTLY like owning a solid state amp with maintenance so far. None. I have had it 3 years with average amount of use. I haven't changed a tube yet. It sounds GREAT.  I would not want to mess with manual biasing. 

If you are planning to use a tube amp, do yourself a favor and avoid low impedance speakers. Your amplifier dollar investment will thank you.

Tube amps using output transformers can lose as much as an octave of bass response going from an 8 Ohm load (using the 8 Ohm tap) to a 4 Ohm load (using the 4 Ohm tap) and the output transformer will run hotter (since more of your output section power will be heating it, not a good use of that power). The amp will make more distortion too and the speaker cables will play a far more important role (and will need to be heavier).

In the old days when tubes were the only game in town, speakers were much easier to drive- they were more efficient. Efficiency is helpful because you get less thermal compression in the voice coils- a more vivacious sound results (IOW this is both measurable and audible).

So a speaker of 8 Ohms (particularly in the bass, so be careful of speakers using dual woofers that might be rated '8 Ohm compatible') or better yet 16 Ohms, along with higher efficiency (+90dB) will help you get the most out of your tube amplifier investment (this is helpful for transistor amps too, since they also make less distortion into higher impedances...).

If you are planning an SET, its helpful to be aware of what you're getting into: If you want the most out of an SET, your speakers must be so efficient that the amp never makes more than about 20-25% of full power. At power levels above that, the higher ordered harmonics start to show up on the transients (where the power is), causing the ear to perceive the transients as 'louder'. This is why you read so much about how 'dynamic' SETs are; it really distortion masquerading as 'dynamics'. To avoid this you need a speaker efficient enough to prevent this phenomena occurring. Of course, SETs have troubles with bandwidth when built to make more power; usually the bass is curtailed in favor of higher frequencies in the output transformer design. This is why the lower powered SETs are known for better sound.

My advice is that the mark of a good system is that it doesn't sound 'loud' even when it is. The dynamics comes from the recording, not the electronics! To that end, the speakers must be easy to drive so that the amplifier is spending most of its time loafing.

Many great suggestions mentioned. I might suggest you watch Roger of Rogers High Fidelity YouTube videos on tube amps & what he feels are important. There are a few really good ones . He knows his stuff! Obviously, he’s also promoting his own brand but very worth it.

His offerings are relatively expensive but in his case, you get what you pay for. I have now for a year his EHF 200 Mark II integrated amp & it is outstanding! Very powerful w/great detailed beautiful tone w/ very good extension at both frequency extremes. It does run hot operating in full class A producing a true 100 watts + / channel but that’s the price you pay for that design & the sound quality it offers.  
 

I’ve owned tube amps & preamps for 40 years; Conrad Johnson, Audio Research, Melos, New York Audio Labs, Art Audio & enjoyed them all. The build & sound quality of Rogers handily beats them all. 
 

My thoughts on important aspects of a a tube amp are: 1- high quality, large power oversized transformers, 2- point to point wiring w/ good wire ( much easier to diagnose & repair should a problem occur) , 3- solid, non resonant  physical construction w/ high quality input & speaker connectors. 
 

enjoy the tubes! Warning once you go there, there may be no turning back. 

As a guitarist, I’m probably overly attached to tubes.  I own over 30 tube guitar amps.  I also own several solid state - digital and analog- guitar amps.  They’re inferior - except for portability and consistency. Tonally, there’s no comparison.  Tubes rule. 

I also own McIntosh, Prima Luna, Manley and several SS  Marantz - Ruby, Reference and a 2230 - hi fi stuff.  

The Manley Stingray  is EL84 based.  In guitar world, EL84 is known to be easier to drive, suitable for low wattage amps and possess a desirable chime at lower volumes.  The Manley fits the bill.   It sounds great, gets to the sweet spot without cranking it up but the bass response is weak.  EL84 based systems require efficient speakers.  Still, a great sounding integrated from Manley.  They build amazing stuff.    But I would probably pass on an another EL84 amp.  

6L6 is my favorite in both hi-fi and guitar sound.  It’s clean, robust, powerful and has a ton of headroom before it gets flubby.  Tubes are easy to find.  The McIntosh integrated is 6L6 as is the Prima Luna separate.   My main guitar amp, a Two Rock, uses 6L6.  In guitar world, what are considered the best clean tones are almost always 6L6 based.  

The Prima Luna integrated uses EL34, 6L6 or KT88.  The KT88 is a fantastic sounding tube but I stopped using them due to reliability issues.  They’re harder to find and their manufacture seems inconsistent.  I’ve had several crash on me for no reason other than I installed them.  But, when working, they were the most hi-fi, clean, round bass, beautiful mids of all the tube types.  

EL 34, which is very popular in guitar, is probably my least favorite in hi-fi.   They’re overly warm, with too much emphasis on the midrange.  But other people swear by them. They’re able to handle a lot of wattage and they’re known for their reliability in demanding, high plate voltage environments.  

My advice, if you’re young, is to buy whatever sounds best in your budge but try to get a system, like Prima Luna, that can handle different tube types.   If you get bored, just roll tubes,  it’s like getting a brand new system.  Chasing tone through tube swaps is a life long endeavor.  I have boxes and drawers full of old tubes.  It’s a great hobby.  Enjoy!!! 
 

No more noisy tubes, better bass extension and tone with SS
No more headaches getting good vintage tubes, no more need for a finicky vintage tube tester, no wasting time tube "rolling", no more worries about Russian supply or Chinese garbage, etc.

This comment is the opposite of my experience.

My tubes are quiet.
My tube amps do a fine job regarding bass with my well-matched speakers.
Vintage tubes are not necessary. Very good tubes are in easy supply and not expensive.
No tube tester has ever been needed.
Tube rolling is for fun and not needed.

I too like EL84 and 6L6 tubes.  The KT66 is pretty similar in sound to the 6L6.  The EL84 must be an easy tube for builders to work with (probably allows for use of cheaper output transformers) because that is where you most often see it being used, but, I like the lively and punchy sound that tube delivers without being harsh.  The 6L6/KT66 are terrific sounding tubes--rich, yet plenty of clarity and good amps running those tubes sound "big" (enveloping soundstage and sense of weight and scale). 

Of the small triode tubes, I like 2a3 and 45 the most.  But, of course they do have limited output and cannot be used everywhere.  

I don't know about the tubes that are used in the output transformerless (OTL) amps I've heard and liked.  Unfortunately, there aren't that many makers of this type of amp because many tend to be unreliable.  That left Atmasphere, a very reliable brand, to this field.  The Berning amps (including the Linear Tube Audio) are sort of variants of the OTL (they are interesting, but for my taste, they are not voiced the way I like tube amps).  Anyone interested in tubes MUST, at some point hear an OTL amp--for some it is like a religious experience--the dynamics and liveliness can be shocking.

With tube amps, more so than solid state, you really have to hear what you are considering for purchase because of the wide range of sound.  While I am a tube electronics person, I find that there are plenty of tube amps that I would not want and I would get a solid state amp instead.  This is particularly the case with high-powered tube amps.  If I really need that much juice (I don't because I don't listen at high volume in a large room), I would consider solid state instead.  

I don't get worked up about tubes wearing out, many of my tube amps from the 60's and 70's still have original tubes. I don't listen to my system more than a couple hours a day, so I haven't seen the tube consumption issue many reference. I don't know much about the brands you mentioned, but I would look toward older proven designs. There are some really great tube amps from the 50's, 60's and 70's, that with the right updates can be very reliable. Long term serviceability is the key to maintained value. Original McIntosh, Manley, Scott, Eico, Pilot, Fisher, Quicksilver, Manley, and a bunch of others hold their value really well. They are also serviceable long term, and are made with quality components. My 3 things would be:

Match the amp to the speaker - the Zu's will open the door to lower watt options that can sound very nice, but might limit your speaker options down the road.

Serviceability- look towards amps / manufacturers that have been in business a long time

Power tubes used- my preference for power tubes are E84 and 6L6. I like the sound of these tubes, and they offer me the power needed to run my not as efficient speakers.      

Bias adjustment has been mentioned. Decide whether it is worthwhile for you to be engaged in that task. If you're ambivalent, a lower maintenance amp such as a PrimaLuna may be suitable. I've been happy with my Evo 400, and sleep soundly knowing the bias is taken care of by higher powers. But if you suspect that you'd enjoy the adventure of tinkering, go for it! I also had a positive experience with a Rogue Cronus Magnum, which has a built-in bias meter. Best wishes!

Now that we know the speakers, I would go with a nice SET amp.  You don't need lots of watts to get those speakers singing. 

Nice sounding OPTs, and strong power supply are as important as anything.  The ability to switch between modes (triode, ultralinear, pentode) is nice.  The more tubes it can accept, the more options you have to tailor the sound to your tastes.  Enjoy!  

Sold all my tube gear except for a couple of guitar amps.  No regrets.

No more noisy tubes, better bass extension and tone with SS, just take my pre-amp out of standby and go...

No more headaches getting good vintage tubes, no more need for a finicky vintage tube tester, no wasting time tube "rolling", no more worries about Russian supply or Chinese garbage, etc.

No worries about dog noses getting burned.

I do miss the cool glowing glass bottles in the dark, but that's about it.

Just my 2 cents.

I also sold my 1936 Ford...

This has been a great thread - which is why I love this site! I will be reading and rereading everyone's comments.

To fill in some gaps and respond to some of your comments - 

Room is an open plan lounge of 9m by 8m. Currently running some 99db efficient Zu's, but have also owned some ATC's before and would not rule out going back to something like that at some point. 

I am lucky enough to be in the middle of an extension that will factor in some room treatment (mainly ceiling) as well as a dedicated power supply.

 

@mulveling  love that detail structure. Great shout on the ability to service outside of the warranty. This is one of the reasons ATC we so great.

 

@larryi  I think you are spot on with to question about attitude. I dont know where I fit on that scale. I have wanted tubes since I was a kid, but always had SS. I dont mid tinkering and enjoy the purchasing of things, but that might be short lived. I also have a family to think about and I dont want them to be "scared" to use it or potentially damage anything. I will live with the Allnic T2000 30th for the next week. and see from there. I also dont want to worry about reducing the amount the kids play in the house if I cant find a good location for it.

 

@clio09 - I wasn't leaving it 15mins before adjusting the bias. I was letting it do is "soft start" which is about 1min before adjusting. the adjustments were very minimal to hit the centre of the bars, but I will leave it longer and see what happens.

@ieales you paint a very real picture here ands my above comment about my family using the equipment gives me something to think about. I am loving the sound, but it is all about balance here. 

@boomerbillone  and @fatdaddy2  - yes I have been thinking about that cost, but again trying to balance it against the enjoyment vs the one off cost of SS. Not sure I can measure that delta just yet.

@njkrebs - I am thinking about that, but was originally trying to minimise the gear I have.

 

Thanks to everyone else for taking the time on this - its a massive help!

 

 

ieales

Make sure you can afford the cost of a periodic re-tube, and select a model whose tube types are still in production.

I'd honestly consider a tube preamp (tube phone) and SS amp. Dan Wright of Modwright has created some absolutely killer gear at reasonable prices. He's also designed an all-tube analog bridge for SS sources. You'd be hard pressed to create a better sounding stack of gear.

Also depends on all of the other factors others already listened like speakers, room specs. 

A couple or three inputs so you don't need a pre-amp. Quality of construction (which does not rule out certain Chifi devices). Warranty and/or a good technician in your area who understands tube amps for when things go south. The efficiency of your chosen speakers.

Features, approach:

• Confirm speakers used long term
• Output tubes, ensure availability, spares
• Quality parts, design, transformers

NOs:

• Avoid cheap junk parts used

 

1. (Big, read 1940s- 1950s NOS) Choke filtered power supply

2. Fixed (manually adjustable) output tube bias

3. 2 times maximum duty rated transformers (power and output)

Bonus round: Point-to-point wiring

@mulveling, man your type of clear and concise information is this is why I read this forum. Very direct an super informative empirical data. Peace ✌️

Hello mpoll1. Not to be a downer - have you considered the cost of replacing tubes? They do wear out in time and die a natural death. One day the amp is working fine and the next day it isn't. A matched pair of output tubes can set you back over $1,000. Are you ready for that? Put $1500 in a savings account and wait. I just had to replace a set of tubes myself. Ouch!  Plan well, listen happily!

Tube amps tend to be more noisy than solid state

Not if they are properly designed and installed.

 

The world of tube sound is vast and very variable--much more so than the sound of good solid state.

Not true. Tube amplifiers are current devices. Many hook up tube amps to roller coaster, Mt Everest peaky impedance speakers. Not the best match. Solid state is  just as variable. A lot of it comes off a production line and is improperly set up. 

Tube gear has a magic that solid state doesn't. If you're a bottlehead, you're hooked for life.

Tube rolling is a fools errand. Tubes are not identical, not even matched sets. Rolling various tubes in and out without any idea of the tube condition and how far it varies from design center is silly. VERY few tube rollers measure and balance different sets and what they hear are level and distortion changes. See ieLogical Rolling

Autobias is nice and generally works very well. However a catastrophic tube failure can take out the AB unless there is other monitoring to shut down the amp. Today, I wouldn't have an amp without it. Most AB circuits allow you to select a preferred bias. It requires a trimmer and a voltmeter and a healthy appreciation for sticking your hands in and around several hundred volts DC. MESSING ABOUT IN A TUBE CAN KILL YOU IF YOU ARE CARELESS.

Nobody has mentioned the driver stage. Some amps have CCS for phase splitter AC balance. Others have fixed resistors that are calculated with an ideal tube, but are seldom exact. Others have a pot for adjusting AC balance. This is the most flexible BUT requires test gear for optimum - read lowest distortion - results.

I see recommendations for autobias.  I much prefer manual bias. I Like to be able to calculate my preferred bias and adjust it.  For example sometimes i run tubes that have a max voltage near my b+, so I'll lower the current a bit and run at a slightly lower plate dissipation power.  Additionally manual bias will tell you if one is biasing much differently than the others, meaning a degraded tube.  

If all this seems like work to you, then go with auto bias.

Jerry

My advice is to download the Decibel X-pro audio app for your smartphone So you can get a rough idea of how loud you like to listen. This will make a big difference. I used to think that high power was required then I got speakers that were 93dB efficient And started listening to 7 and a 1/2 W. And I loved the sound then I went down to one and a 1/2 W and love it even more. But I’m listening right around 70 to 75DB and fairly close to my speakers. This wouldn’t work for a lot of people.

 By the way, I think you're getting a lot of good advice on this thread actually. Ultimately you gotta think of things in terms of a system. And the speakers in the room and the amount of stuff you have in the room is part of that system. Donnie Darko (?) has a good YouTube video about room treatment that's worth checking out. 

You didn’t mention Tube Preamp, which I think is more important regarding features and system sound

1. my Cayin A88T Integrated Amp, Bias Controls

I wish it had exterior bias meter and controls. Someone else mentioned auto-bias, that would be even nicer. Unfortunately I need version 1 as it is the only one with 16 ohm taps, and it’s bias adjusters are inside, take bottom off, better avoid touching ...... Great review made me pick it, but I wasn’t paying attention to bias controls.

Preamp Features: My McIntosh mx110z is a full featured Tube Tuner/Preamp, up to spec by Audio Classics, especially new gold rca jacks. I started with Receivers, then separates, then no controls, now back to full features, integral phono and tape .... Vintage McIntosh units have their MODE switch, which is very helpful for me to match my speakers side to side when messing with level controls, stereo reverse, l to, r to mono .... Not everyone needs the Mode control, but I do.

2. IF I went for an Integrated Amp, with remote features, I would definitely want at least remote balance as well as remote volume. My Cayin is an integrated amp, but I only went for that to get remote volume so I could stick with my Vintage Preamp. I only use 1 input, and I think remote control inputs is dumb.

There are many errant tracks that benefit a LOT from a small tweak of balance, especially compilation cds/lps/tapes. A lot of recorded live performances, the 1st track, eh, not quite right, the room with people in it is different than the pre-concert set-up. the engineer figures it out, makes slight corrections for the rest of the recording,

3. IF I didn’t have level controls on my speakers, then I would like to have enough tone controls (not a full equalizer, but several bands, not just treble/bass).

That’s hard to find on modern equipment. I just don’t believe in buying a great speaker and expecting it to sound great in .... unknown room. Much room treatment results from the lack of level controls/decent tone controls that can be refined using a sound pressure meter (quite affordable these days).

 

Quality transformers are a key part. That's why I like Quicksilver.

https://www.bandwidthaudio.com/post/output-transformers-the-heart-of-a-tube-amp

What speakers. A VERY important consideration. Auto bias, tube rolling ability, quiet design

what speakers?

different tube amp qualities and features matter if you are driving hyper efficient altec horns or audio notes, less efficient harbeth monitors, reactive focals or revels, or resisitive magnepans

just like ss amps, they should be optimized to the speaker load and power/current demands

right?

The most important features depend largely on the buyers attitude and expectations regarding components.  If you are someone who is bothered by having to maintain/fix gear, or are bothered by the fact that tubes start to go bad from the moment they are turned on, then tubes are not for you.  To the extent you have some tolerance for the nature of tube gear, but, you are still concerned about tubes wearing out, that might affect the kind of gear you should buy.  The type of tube chosen, and how hard the particular amp drives those tubes, are BIG determinants of how long tubes will last.  There are amps that will run for many decades without the tubes having to be changed, others might need new tubes every couple of years (or earlier).   Tube amps tend to be more noisy than solid state--hiss or hum or intermittent crackling, etc.--you need to factor in your personal tolerance in deciding what to buy because some otherwise great sounding gear might be prone to be noisy.

For all kinds of gear, not just tube amps, decide what features are necessary.  To me, remote control of volume and some form of balance control is essential.  Given the nature of tube gear, I would think that small channel imbalances are inevitable and the ability to compensate with a balance control is a must.

The world of tube sound is vast and very variable--much more so than the sound of good solid state.  You need to listen to enough gear to determine what fits your ear.  Personally, I don't think there is only one type of tube topology (e.g., single-ended triode) that is clearly superior to another, but, there are some listeners that have a clear preference.  I have heard versions of pushpull pentode/tetrode amps, single-ended triode and output transformerless amps that sound terrific, often in quite different ways.  I think the type of tube, and the brand of tubes matter too, but again, these are personal preferences so the only recommendation is to hear plenty of different examples to develop your own idea of what to buy.  Finding a friend and/or a friendly dealer that can help you sort out options would be a big help.  If you attend a big audio show, you can also taste different gear or find people that can help you make the right choice.

I have an allnic in the house now and need to adjust bias every time I switch it on - is this normal?

@mpoll1 No it is not. Are you allowing the amp to warm up for 15 minutes or so before checking bias? Bias should be pretty stable once it is set. As tubes age it may need to be adjusted, and at a certain point they they will need replacement if you cannot get the amp to bias properly. I prefer amps with fixed bias vs. cathode self-bias, but I have access to a computer tube tester and a huge stock of tubes so I can ensure well matched tubes for use in any of my amps.

 

Thanks all. @jjss49 I deliberately left out that detail as I was looking for a 1st pass on features. But understand your point. The listening space is an open plan 7m by 9m. There won’t be any decisions without home demos. 
 

@mulveling this is great information- I really love the point about out of warranty service and auto bias. I have an allnic in the house now and need to adjust bias every time I switch it on - is this normal?

I second the auto bias feature is great to have,flexibility in which tubes to use,and a gain control and feedback control are nice features. Point to point wiring is a big plus - simple to upgrade parts and repair if needed.

 

• Auto-bias circuity (this applies to push-pull topologies) is lovely, and usually includes superior protection & status indicators that are preferable to fuses. I’ve had a tube fuse blow and it wasn’t even immediately apparent that single tube was out (multiple push-pull pairs per side). I’ve also had a fuse fail to trip when a KT90 failed "spectacularly" and fried a resistor (and singed the PCB).
• These days it might be wise to choose an amp that DOESN’T lock you into future Russian tube supply, e.g. KT90, KT120, KT150, KT170.
  KT88 are nice, reasonably high power, and have non-Russian alternatives available.
• You might first decide what power level you’re looking for and branch from there. Low power opens up options like DHT (direct heated triode), SE (single ended, aka pure class A), and SET (single-ended triode - usually SET and DHT go together, e.g. 300B tubes). Medium power can be hit by either big DHT tubes or medium size tetrodes / pentodes like EL34 and 6L6GC. Some say those tubes still sound sweeter than the big tetrodes like KT88 - KT170 (and I’d tend to agree). For high power, you’re looking at class AB push pull, KT tubes 88+, and (often) multiple paralleled push pull pairs.
• Amp driver circuits are often overlooked and definitely affect performance. I’m not a fan of 12AU7 here. I think 6SN7 is a lot better, for starters.
• Always look at the service history for a brand. You want a brand that takes pride in its products and will service old out of warranty units without either balking or acting like they’re doing you a huge favor. Ideally, they will be based in your country. And really ideally, point to point wired amps are generally more serviceable (especially in the long run) than PCB based.

@jjss49 My answer is useful, he just has to design the rest of his system around a DHT SET.  :-) 

 

op

you won't get useful answers back if you don't describe the rest of your planned system, especially speakers, room size and musical taste

Not gonna lie, I had to google that. Do amps need to be DHT “ready” or are you saying make sure you get those types of tubes?

DHT

DHT

DHT