EL36 SE Triode from ETF 2006 build

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Paul Barker
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#1 EL36 SE Triode from ETF 2006 build

Post by Paul Barker »

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with a couple of changes, yet to put ultrapath cap value in as need to get all facts and I’ll do the calcs on the bypass cap in the same process. Im sure 330 is excessive. The grid choke speaks for itself.

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So I was saying on one of the other of my project page. Ive decided that for a single ended amp its best to start with a pentode. Then I found the actual cirquit used at ETF 2006, so Ive got a suitable pentode design handed to me on a plate. Ive ordered a pair at £20 plus delivery £6. I can have a rest from designing my own cirquit, because I cant fault this cirquit. The designer is not greedy for maximum power out. As I am finding with my EL34 design less power is much better sound.

Ive now writen a spreadsheet to calc 2nd and 3rd Harmonic on SE valves.

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So the above cirquit is my next build. AS RF valves I’ll adheer to Mike’s warning about g1 and g2 stoppers.

The EL822 push pull is second build.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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Paul Barker
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#2 Re: EL36 SE Triode from ETF 2006 build

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I’ll consider moving the el34 out of its chassis and fit it into the new smaller chassis. Depending if I can reduce the bypass cap as it would require 6 big poly caps as it stands and Im not using electrolytics, Ive heard better, Im not going backwards.

The bypass cap calk for existing cap in the El34 amp, which Id carry forward to the EL16 is -3db @ 3.4hz recalced for the EL36 so to speak. the ultrapath value is 16uF for mu plus one as a fraction of the main cap Mu +1 is 5.5.

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Paul Barker
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#3 Re: EL36 SE Triode from ETF 2006 build

Post by Paul Barker »

16uF ultrapath cap ordered QTY 2
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#4 Re: EL36 SE Triode from ETF 2006 build

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I’m sorry I was struggling with the 3rd harmonic distortion formula, so went back to Stephies teaching on distortion, read it multiple times, added 4th harmonic so I now have a spreadsheet that calculates 2nd 3rd and 4th. Stephie explains the negative figures. They are not a calculation error. I guess the distortion is no little its reported negative.

Triple checked all my numbers. Then took all my measurements out and put Stephies measurements for the fictitious valve tested. My calculator got them all right. So now I know I’m showing the correct distortion profile for the EL36 from ETF2006.

What is a surprise is the level of 3rd matches the 2nd near enough. This only pertains to the individual valve alone has nothing to do with the effect of the driver. Im now a little perturbed. Also listening to my distortion reduced EL34 amplifier and dont really want to lose that aural memory and the chance to show how that sounds compared to how the EL36 from ETF sounds. The only way to do this is leave this amp alone, but move the output transformers off board. So a boxed plug in board pushed into each amp on two pins with a set of speaker out unions.

So it becomes a quick in and out job.

Here is the distortion, not as Stephie said 4th is so low its negative. But 3rd is remenicient of 801@. Kind of not sure about this new finding.

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So Ive calcd the El34 amp as it plays today, which is beautifully. Its only delivering 2.16 watts. Bear in mind when you see the results at 1.95 watts the triode connected EL84 is 9% 2nd according to the Vade Mecum.

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This explains why the EL34 triode at the EL84 power out is a really sweet valve.

There is far less third than the EL36 too. And the use of the pentode driver would make that situation worse. This is a bit of a surprise. And I’ll pause for thought. I think I have landed at a special point in the EL34 I should cherish. And Im at a point where I must question the viability of the EL36.

Its good that you have the two distortion charts. You can see the EL34 is operating with greater current. I straight way loved it and mentioned it. I shall do some playing with shifting the EL36 into a similar zone and lower power. To see if that 3rd goes away. I’ll be back. By the way at home 2.1 watts is enough.
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#5 Re: EL36 SE Triode from ETF 2006 build

Post by steve s »

I had a radford mk3 EL34 amp I was very impressed with that at the time, I wouldn't be trying for more than a watt from a trioded el84 though

I've always fancy trying out my vt75a on an se amp.. one day ... id hope the early versions the one to use
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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#6 Re: EL36 SE Triode from ETF 2006 build

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So I shifted the EL36 operating point to 2.3 watts and to highest current I could, also pushed dissipation up to 20w limit; the 3rd h distortion speaks for itself.

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I don’t see a 300b challenger.

This will not be the next project. I’ll just shelf it. Shame I ordered the resistors and caps. They’ll come in handy somewhere.

It just goes to show, don’t trust everything others say even if its in print from a specialist event.
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#7 Re: EL36 SE Triode from ETF 2006 build

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Yes Steve Im going off the EL84 aswell. But the EL34 at 2.1 watts is a keeper. Its the winner of this excercise. I see no point building an amp loaded with odd order distortion.
I cant go out so I’ll play with other characteristic curves at 2 watts. Its a shame I dont think I can get more than a watt from 6EM7. But I’ll now have to look at PX4 if we’re in this 2 watt teritory. El84 is barred if it has to be contested at one watt. I cant have a one watt amp these days. Actually surprised this two watt amp is doing the job.

Stephie who devised these distortion tools suggested feedback from output anode to driver, by the way at the end of his series about distortion. that was plajurised by Alex! Why do I say that? Because he doesnt give his sources. I always comment where I found the knowledge. Anything else is plajurism.
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#8 Re: EL36 SE Triode from ETF 2006 build

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I guess the distortion is no little its reported negative.
That's not how numbers work. Just saying.

I would. Guess the -ve indicates the distortion results in the amplitude being less than linear (0%) as opposed to greater.
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#9 Re: EL36 SE Triode from ETF 2006 build

Post by Paul Barker »

This is what Stephie said about the negative in his example 3rd

“Notice the minus sign. This indicates that the harmonic content subtracts from the fundamental (flattening it) when the fundamental is at its crest. This *usually* happens on third harmonic distortion in tubes.”
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#10 Re: EL36 SE Triode from ETF 2006 build

Post by Nick »

So what I said then.
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#11 Re: EL36 SE Triode from ETF 2006 build

Post by Paul Barker »

Yes
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