What's the best audio output valve?

[Peter.N.]

I always used KT66s in the heyday of valve amplifiers but I would think colour TV line output valves would give lots of power although I don't know if their characteristics would suit audio. There are lots of PL509s and 519s about probably for very little money, I have a box of them complete with bases and top caps.

Peter

[Herald1360]

Is the EL503 an example of Philips's being coy about beam tetrodes? From the look of its characteristics it would seem not to be a pentode.......

[Heatercathodeshort]

A while back I built a 78 rpm gramophone from 'junk' parts that were literally kicking about in my extensive junk box [s]!

https://www.vintage-radio.net/forum/...ad.php?t=97914

The final version of the amplifier consists of a 6F13 preamp [TV RF amplifier] feeding a 6L6G into a Radiospares 'Heavy duty output transformer'.
It gives excellent results on 78 records and recently I fed some test card music via a CD player into the amp.
I must say I was astonished by the quality and presence of the audio quality. It is very nice to listen to with plenty of output from the pre war speaker employed. It is all I could wish for.
My favorite? It must be the humble 6V6/G, the big black Brimar one with the black anode. That must be the secret or maybe the unknown powers of the little Mazda 6F13..
I may take it to the garden party at Dulwich on Saturday. Regards, John.

[richrussell]

Is nobody going to suggest the UL41 as a candidate for best output valve then?

[dominicbeesley]

I bought a load of tiny soviet 1p24b-v pentodes, they're tiny but are rated for 1.3W into 50ohms....On my pile of round tuits is a parallel push pull UL amp.

[Herald1360]

Can you do UL with those things? I suppose they have some affinity with beam tetrodes in the sense that all their "grids" are beam focussing rods.

[Restoration73]

I was very pleased with an amp I built for an enthusiast. ECC83 strapped as a single triode driving a 6L6GC and a RS Hygrade audio transformer. Class A of course.

[steviewonder]

No- one has mentioned the Mullard EL84 yet. A super valve in my opinion!

[dominicbeesley]

Originally Posted by Herald1360

Can you do UL with those things? I suppose they have some affinity with beam tetrodes in the sense that all their "grids" are beam focussing rods.

It looks that way - when I've got some time I'm going to have a good play with them and see how they can be configured. I've seen all sorts of weird and wonderful configurations.

D

[mole42uk]

Originally Posted by steviewonder

No- one has mentioned the Mullard EL84 yet. A super valve in my opinion!

Agreed. I've just had a notion of using four per channel for my 20W amplifier.

[G6Tanuki]

Originally Posted by steviewonder

No- one has mentioned the Mullard EL84 yet. A super valve in my opinion!

I generally preferred the little 6BW6 (essentially a 6V6 shrunken to fit in an all-glass B9A bottle) over the EL84. The 6BW6 has lower heater-demand for a start! And the prices are less horribly inflated.

In push-pull you can get 30 watts or so from a pair.

[PE9ZZ_JO22KI]

Hands down PL519. Most bang for your buck! And remember, even McIntosh used line output tubes in their designs.

@Herald1360: the EL503 indeed is a beam power tetrode. There's a Funkschau article from 1966 (when it was introduced as successor of the EL34) pointing this out.

Tjerk, 9ZZ

[barretter]

Originally Posted by G6Tanuki

In push-pull you can get 30 watts or so from a pair.

30 watts, really? The Brimar spec-sheet gives 12 watts max in Class AB1. It seems virtually identical to an EL84.

[DangerMan]

It's true, that's what Brimar claimed, but working in class AB2.

It isn't recorded how well they last though!

The snippet is from the full Brimar datasheet which is too big to post.

Pete

[GrimJosef]

Originally Posted by barretter

30 watts, really? The Brimar spec-sheet gives 12 watts max in Class AB1. It seems virtually identical to an EL84.

It's 30W in Class AB2 (full details in Brimar Application Report VAD/507.8 http://frank.pocnet.net/sheets/184/6/6BW6.pdf). The output stage is then very compact. But the power supply and driver stage are non-trivial. And it's important to keep the whole lot very well ventilated.

Cheers,

GJ

[bikerhifinut]

Originally Posted by steviewonder

No- one has mentioned the Mullard EL84 yet. A super valve in my opinion!

I always thought EL84's were very good value for money in as much as you can get a very good later manufacture valve for a tenner or less each, compared to the cost of a Kt88 for instance.
At the risk of upsetting some people I think the Mullard valve was/is a bit overrated. Probably because I havent heard a new one, most of the ones out there are probably on their last legs. I rather like the Russian 6P14P-EV version, which can take a higher anode voltage and has a higher anode dissipation AfAIK. And I got em for a fiver each................ and yes I think they are a super little valve, 10watts in push pull is plenty in most normal domestic setups despite what the hi fi comics would have you believe. Even with modern speakers.

[barretter]

Originally Posted by GrimJosef

It's 30W in Class AB2 (full details in Brimar Application Report VAD/507.8 http://frank.pocnet.net/sheets/184/6/6BW6.pdf).

I don't fancy the 7% harmonic distortion!

[G6Tanuki]

When you're driving it from a carbon microphone and the audio-response is filtered to 300-3000Hz either side of the speech-clipper, 7% harmonic distortion's not going to be noticed!

[mole42uk]

I think I'll stick with some new Russian 6P14s (EL84), four per side developing about 20W per channel and running nice and cool. RS sell 6P14s for £7 each including VAT even if they are out of stock today!

[GrimJosef]

Originally Posted by barretter

I don't fancy the 7% harmonic distortion!

Assuming that that's the dominant distortion then with 26dB negative feedback (Harold Leak managed that back in the 1940's) you'd be down to 0.35% which isn't too bad. It's the same as the EL84-based Mullard 5-10 when that's operating at just 10W and it's three times better than the stock version of the much loved Mullard 3-3, for example. If you drop down to 25W then the distortion drops by another factor of two (see the graph on the 28th page of the Application Report) and I reckon you could make a decent case for that being hi-fi .

Cheers,

GJ