What's the best audio output valve?

[mole42uk]

Hi,

I have been musing about building a new audio amplifier for some time now. I used to have a Leak Stereo 20 and have used and liked the EL34, with its several faults, for a long time. I have a pair of Keesonic 'Ranger' loudspeakers which need an amplifier of around 20W in my room. My listening tastes range from Bach to Pink Floyd and from solo violin through to church organs.

With a clean sheet of paper, and a bank balance that will support the correct transformers, what would you use for the output valves?

[maninashed]

A valve is just that, a valve. Its mainly a question of good design and layout AND the quality of the O/P transformers. I have a Leak Stereo 20 with EL84s, it sounds fine, I also have a pair of Leak TL25+ using EL34s in daily use, they sound excellent too. The common factor is the quality of the Leak O/P transformers. That's not to say a well designed amp using say 807s wont sound good, at the end of the day its quality that counts.
Bill

[n_r_muir]

Hi,

In the 1960's I built my first power amplifier using a pair of 807's operating push pull with 350 Volts on the anodes supplied from a 5U4G. I used a 6SN7 as the phase splitter and another 6SN7 provided two stages of voltage amplification and Baxendale type tone controls. To me it sounded really good!! It was eventually replaced with a pair of Quad II's.

My point is that the "conventional" range of output valves such as PX4, KT66, KT88, EL34 etc, all seem to attract silly prices on auction sites whereas the 6L6 and 807's are still available at sensible prices and they will prove the 20 Watts or so of good quality audio that you require. Also to run the full 20 watts you will need either a detached house or very understanding neighbours!

[turretslug]

I think that there is an element of snobbery (amongst all the other vices...) in the audiophile scene- the 6L6 is for guitarists (sniff), so hopefully the various makes/versions shouldn't go stratospheric in price. The KT66 seems to have been a developed 6L6, optimised for good linearity in audio PA use but, as the others say, good output transformers and competent design generally ought to even up many of the alleged differences.

[terrybull]

I will probably be pilloried here for daring to say this but I replaced my Leak Stereo 20 with a Linsley Hood 1969 class A. It simply sounded better although in its standard form it's only 10 watts. I have no bias to valve or solid state and let my ears be the judge.

[turretslug]

No pillorying here!- only pragmatism. In the end, a very nice solid-state amp is still possible for the same price as a basic valve amp and its list of advantages is as long as your arm. A valve amp build is an interesting diversion rather than a vital recourse for hi-fi but entertaining and harmless nonetheless.

[mole42uk]

Please! I don't want this to get into a valve/transistor debate. That decision is already made.

As several people have noted, the transformers are a vital part of the set-up. Those who read in full the original query will remember that I said "a bank balance that will support the correct transformers" which may lead one to think that I know how important they are.

If I could get a couple of Gardners AS.7034 or Parmeko P2647 I'd be a happy man!

[PE9ZZ_JO22KI]

There's no such thing as "the best audio output valve". Given budget and OPT a pair of PL504s will perform just fine even though they're line output tubes. I've built a crude 100W amp with two PL36 and a crap transformer many years ago... As said above it's very much a matter of taste. I now have a nice quad KT88 (were EL34s) modded China amp with better transformers (Amplimo toroids).

Tjerk, 9ZZ

[Skywave]

The first two sentences in post #2 are highly apposite: I'd like to expand on those.

You can take the design of anything - not necessarily electronic - and spoil that design by a poor choice of just one item or feature within it. In the real world, it is simply not possible to attain 100% perfection with anything: a balance has to be struck: a compromise that minimizes the effects of the weaknesses of any individual item within the total design. And when such a design is as near to perfection as is realistically attainable, that's when the problems begin, since the tiny 'zone of imperfection' that remains is notoriously difficult to quantitatively assess. At that point, qualitative judgements are made, which are, by nature, purely subjective. And in the 'hi-fi game', that usually gives rise to so-called 'audio-foolery'.

Al.

[threeseven]

Interesting question but I don't think there is an answer. Can't imagine anyone would ask what is the best audio output transistor.

[terrybull]

The best amplifier(s) I ever heard were single ended with a 300B output triode. It was a pair of mono blocks that were ludicrously expensive and heavy with I believe silver wire in the output transformers. I know I am perhaps straying into the realm of audio foolery but boy, did they sound nice. So my vote has to be for the 300B.

[GrimJosef]

Originally Posted by terrybull

The best amplifier(s) I ever heard were single ended with a 300B output triode. It was a pair of mono blocks that were ludicrously expensive ... boy, did they sound nice. So my vote has to be for the 300B.

The critical point is that they were ludicrously expensive. I'm afraid you can't learn anything about the 300B from this unless you can compare it with an amp using a different valve that has had the same amount of money spent on it by someone with a similar level of design expertise. Different valves bring a range of different factors to the design exercise - linearity, anode impedance, drive requirements etc. Valves which are more linear make the designer's job easier and allow him to 'spend' his (usually) limited resources improving something else - the output transformer, or the feedback loop design, or the phase-splitter balance. One example of a particularly good amplifier (in terms of its objective performance) is the Radford STA15 (later the Radford STA25). This used EL34s in the output stage. Perfectly good modern EL34s can be bought for less than £15 each (e.g. http://www.hotroxuk.com/jj-valves-el34.html) and, with the right output transformer, will deliver a level of objective performance at the 25W/ch level that will be very hard to beat with any other valve. The price difference between these and any cheaper valves will, given what has to be spent on a high quality output transformer, be negligible.

Cheers,

GJ

The best output valve, these days get one that is still made, Rapid Electronics sell new EL34's for not a lot of money. A good output transformer is needed too, Lundhal (sp?) do very good ones for about £180 a pair for push pull output. VVT also do quite good ones for a lot less. Do use negative feedback, it does improve amplifier performance a great deal.

[Radio Wrangler]

It doesn't really matter what you choose. A very good amplifier can be designed with almost anything.

I'd rather save remaining 300B, PX4, and KT66 period stock to keep going the equipment in which they originally belong. New construction ought to use currently made parts.

That still leaves some very suitable devices, though without the rarity and price which gives some devices a special glamour.

Pick something which loafs along and has a good reputation for longevity.

David

[mole42uk]

Has anyone any experience of the PL36 in a 43% screen-grid P/P output stage?

With the right transformer, that should make the right sort of noise.....

[Malcolm G6ANZ]

A friend of mine once built an amplifier for a large PA system. He used a pair of 4cx250b's into a massive transformer. I think it ran with 1kV on the anodes. It ran incredible power to the 100v line system. The PA was used at the Longleat radio rally for several years. Maybe not classed as HI-FI but it did the trick, just shows that (almost) any valve can be used at audio.

Malcolm

[Ed_Dinning]

Hi Richard, why not have a go at your own transformer design?
For push-pull and UL it is not that difficult, only tedious if you have as many sections as a Williamson.
Modern materials (Unisil lams are more linear), grade 2 wire and polyester insulating tapes all make some improvements.

Ed

[kalee20]

Originally Posted by threeseven

Interesting question but I don't think there is an answer.

Absolutely - not till you quantify 'goodness' as a single number, which can then be put in order for different valves. Then you choose the valve that the highest number corresponds to.

So, do you include cost as factor in your figure of merit? Sensitivity? Size? Linearity? Power handling?

The UL84 is undoubtedly one of the best valves for producing a decent output from a small signal. A KT66 would be rubbish in this position. A nice fat triode such as the PX4 provides a good linear output, with inherently plenty of damping on the loudspeaker - but it is not sensitive and needing a hefty drive signal leads to the possibility of greater distortion in the drive stage, than would perhaps an EL84. Or how about ten 6SN7 double trides, in parallel push-pull, versus a pair of 6V6's? Which would you consider as 'best?

Personally, a pair of 6L6's, conservatively run, should be about as good as you'll get.

[Alistair D]

Originally Posted by mole42uk

Has anyone any experience of the PL36 in a 43% screen-grid P/P output stage?

The link is for a guitar amplifier but explains what is required.

http://www.chambonino.com/modify/giumod1.html

Al

[PE9ZZ_JO22KI]

EL503s are wonderful tubes. Too bad they're so rare having come so late in the transition to transistors.

Tjerk, 9ZZ