New SE With Triode Mode KT120/150

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Cressy Snr
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#466 Re: New SE With Triode Mode KT120/150

Post by Cressy Snr »

steve s wrote: Mon Mar 22, 2021 8:41 pm Looks great Steve.. who would have thought you’d be back to el34's... not me !
I’ve tried all sorts as you know, but there’s something about EL34s in triode mode that I find irresistible.
It does sound better than the single ended EL34 amps I’ve built in the past, which of course has brought out more of the magic, so it’s win-win. The trioded EF80 driver is the game-changer in this case I think.
Last edited by Cressy Snr on Tue Mar 23, 2021 3:18 am, edited 1 time in total.
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Cressy Snr
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#467 Re: New SE With Triode Mode KT120/150

Post by Cressy Snr »

Greg wrote: Mon Mar 22, 2021 8:16 pm Now you’ll have to dig the garden :roll:
Funny you should mention that. I’ve got a load of tree branches to cut up by hand tomorrow.
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#468 Re: New SE With Triode Mode KT120/150

Post by steve s »

Cressy Snr wrote: Mon Mar 22, 2021 9:31 pm
Greg wrote: Mon Mar 22, 2021 8:16 pm Now you’ll have to dig the garden :roll:
Funny you should mention that. I’ve got a load of tree branches to cut up by hand tomorrow.
Thats sounds better than my 2 to 3 days of painting I have ahead of me..
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#469 Re: New SE With Triode Mode KT120/150

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Cressy Snr wrote: Mon Mar 22, 2021 9:31 pm
Greg wrote: Mon Mar 22, 2021 8:16 pm Now you’ll have to dig the garden :roll:
Funny you should mention that. I’ve got a load of tree branches to cut up by hand tomorrow.
Sod that, get the chainsaw out
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#470 Re: New SE With Triode Mode KT120/150

Post by pre65 »

Ant wrote: Tue Mar 23, 2021 9:08 am
Cressy Snr wrote: Mon Mar 22, 2021 9:31 pm
Greg wrote: Mon Mar 22, 2021 8:16 pm Now you’ll have to dig the garden :roll:
Funny you should mention that. I’ve got a load of tree branches to cut up by hand tomorrow.
Sod that, get the chainsaw out
Ah, the chainsaw. :)

Somehow, the mere thought of cutting into wood with a chainsaw is very appealing.
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#471 Re: New SE With Triode Mode KT120/150

Post by Mike H »

:D

Interesting journey, it keeps evolving!
 
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#472 Re: New SE With Triode Mode KT120/150

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Interesting journey, it keeps evolving!
Aye, it has certainly changed out of all recognition from the original ideas. At the start I was after power, hence the desire to use KT120s or even KT150s. But that all fell by the wayside and I ended up in a dead end. It took a conscious decision and quite a bit of mental effort to try and actually design the thing for low distortion rather than merely hope for a low distortion end point. I got there eventually. A couple of Watts of trioded EL34 will do me.

Today I fitted a pair of never-been-used, Russian military, K72-n teflon coupling caps. Simon gave me these, sometime around 2007, but I couldn’t think of anywhere to use them, due to their 0.033uF value.

Because of the very high value grid leak resistors on the El34s, with these low value caps, I was still able to get the LF -3dB point to a reasonable 9Hz ish; higher than the 1Hz ideal yes, but it’s only a two stager and the slightly worse LF phase shift performance is not a problem subjectively. These caps are the icing on the proverbial.

Also the very high grid resistor values (500K in reality, rather than the 470K on the schematic) mean that KT anything apart from KT77 which below 25W plate dissipation allows 1Meg, is completely out of the question, so fiddling is pretty much prevented.

It’s actually a great amp now. I was up until turned 3am the other day playing records (see the edit time on post 466.) That has only happened twice before, in the last 40 years, so I must have got something right. :)

I mean, the thing is, Hi-fi component designers and some reviewers like to talk about realism as their ultimate goal, but that’s not a thing for me. OK, so when playing the 0.1% of very high quality recordings on a super-linear, wide bandwidth, low distortion system, situated within a properly treated listening space, you might just about be fooled into thinking people are playing music in your room, but I don’t care about that. In the end, all I want is for things to sound good.
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Mike H
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#473 Re: New SE With Triode Mode KT120/150

Post by Mike H »

Yep same here really! If it's listenable and not giving you earache and you want to keep playing stuff :D
 
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#474 Re: New SE With Triode Mode KT120/150

Post by simon »

Cressy Snr wrote: Wed Mar 24, 2021 3:54 pm Today I fitted a pair of never-been-used, Russian military, K72-n teflon coupling caps. Simon gave me these, sometime around 2007, but I couldn’t think of anywhere to use them, due to their 0.033uF value.
Those were the days when Russian caps and valves were dirt cheap! I thought they were 47nF or 56nF, I used them for coupling in a 45 amp. They were probably a quid each or summat.

I bought some HUGE silver micas too, only cos I spotted them when I was buying the teflon caps, 20p each or something.
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#475 Re: New SE With Triode Mode KT120/150

Post by Cressy Snr »

Yep, I remember you said they were pretty cheap.
They certainly sound good in this particular application.
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#476 Re: New SE With Triode Mode KT120/150

Post by steve s »

I had a box full of those k72 caps I was selling them very cheap at radio rallies, it was only last year I used some, and was quite surprised how good they where
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#477 Re: New SE With Triode Mode KT120/150

Post by andrew Ivimey »

I too think they are fine and really, in the grand scheme of things, o.o3 is sort of in the middle of ....
Well anyway, I'd never do it but I'm sure we've all read of peeps putting a teflon cap say in parallel with a lesser cap to 'improve' the sound.

Why are those Soviet teflons so big though?
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#478 Re: New SE With Triode Mode KT120/150

Post by IslandPink »

Teflon has lower dielectric constant, for starters.
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#479 Re: New SE With Triode Mode KT120/150

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andrew Ivimey wrote: Fri Mar 26, 2021 11:30 am

Why are those Soviet teflons so big though?
And i thought they were a little small to be any good..
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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#480 Re: New SE With Triode Mode KT120/150

Post by IslandPink »

Really ?
Most of the values they sold are are low. If you get a 0.1uF one, they are large.
I have a box full upstairs. Unfortunately I prefer good quality polypropylenes nowadays.
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