New SE With Triode Mode KT120/150

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andrew Ivimey
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#481 Re: New SE With Triode Mode KT120/150

Post by andrew Ivimey »

I've a few 0.22s @ 600volts. Lovely and huge.

For coupling polypropylene are darker than the gorgeousness of teflons but really, that's only my take and if other peeps prefer something else then I wouldn't even begin to argue the point.
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.
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Paul Barker
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#482 Re: New SE With Triode Mode KT120/150

Post by Paul Barker »

steve s wrote: Fri Mar 26, 2021 8:18 pm
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..
In that case a grid choke to shift high pass lower.
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#483 Re: New SE With Triode Mode KT120/150

Post by Cressy Snr »

The amp has gone through more simplification over the last week or so.
The power supply has just the one choke now (10H/300mA) and the branch to the input stages is a simple pair of cascaded RC filters.
I figured that there was no need for all the shunt reg, VR tube gubbins or the additional choke. Nothing wrong at all with RC filters if they are only dealing with 17mA of current, I've just found.
The revisions simulated really well in PSUD, giving vanishingly low ripple at the input valves for not a lot of capacitance.
The output stage feed became a dead simple RCLC setup, (47R/50uF/10H/50uF.

There has been nothing lost in terms of the sound quality. If anything, the treble is a bit clearer and sweeter. Bass hasn't suffered any additional looseness, so I'm very happy with the result. There is no hum.
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The amp is now free of 'assumptions' (copyright NickG.)
It is silent in operation, both electrically and mechanically and sounds good. Couldn't ask for more really.
Last edited by Cressy Snr on Sat Apr 03, 2021 6:11 pm, edited 2 times in total.
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#484 Re: New SE With Triode Mode KT120/150

Post by Cressy Snr »

From this:
3stage.jpeg
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To this:
Simple.jpeg
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As simple as it gets.
A bit like me. :)
IMG_0622.jpeg
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Just need to find something to make a plate to cover all those holes where the complication used to be.
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#485 Re: New SE With Triode Mode KT120/150

Post by Cressy Snr »

Shame it had to end like this really. I had hoped for some kind of enlightening experience, but in terms of power supplies: all around the houses and back it is. The old ways work perfectly adequately. I now know how to design for low distortion though. :)
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#486 Re: New SE With Triode Mode KT120/150

Post by steve s »

Cressy Snr wrote: Sun Apr 04, 2021 8:55 am Shame it had to end like this really. I had hoped for some kind of enlightening experience, but in terms of power supplies: all around the houses and back it is. The old ways work perfectly adequately. I now know how to design for low distortion though. :)
Well that's something steve... a good experience!
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Ray P
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#487 Re: New SE With Triode Mode KT120/150

Post by Ray P »

Cressy Snr wrote: Sat Apr 03, 2021 4:19 pm Just need to find something to make a plate to cover all those holes where the complication used to be.
Maybe try getting someting 3D printed Steve?

https://www.audio-talk.co.uk/phpBB3/vie ... =11&t=8143
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#488 Re: New SE With Triode Mode KT120/150

Post by Mike H »

Cressy Snr wrote: Sat Apr 03, 2021 4:16 pm The amp has gone through more simplification over the last week or so.
<snip>
Image

At least you've tried other stuff to see what happens, and found it's not necessary in the end. Nowt wrong with that.

In the old days of course, designers had to design down to a budget (not least, the tax on valves)
 
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#489 Re: New SE With Triode Mode KT120/150

Post by Cressy Snr »

Aye it certainly was educational and TBH I’m glad that I prefer the sound of ‘simple.’ Apart from the series regulated (6080) power supplies I had on the 6B4G monoblocks, which were dead quiet. I’ve never achieved a power supply as quiet as this one is. It equals the 6B4G power supplies for quietness. Regulation will be poor of course, but you can’t have everything if you are going to go with simplicity: it’s a matter of what you are prepared to do without in the name of it.

I don’t feel I’m short of anything, but someone else might immediately notice something missing. It’s all down to individual preferences and expectations, but in the end, you have to go with what suits you and importantly, try to make the best sound for the budget you have.
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#490 Re: New SE With Triode Mode KT120/150

Post by Cressy Snr »

A little bit of refinement, both electrically and cosmetically, since I last posted on this thread:
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A cover has been fitted over the toroidal mains transformer, the choke has been changed for a potted 4H 200mA job, and the preamp stage power supply caps have been changed for a JJ 500V double can cap. The rectification is now a pair of 6CJ3 TV damper diodes in a hybrid bridge arrangement.
It looks a lot better I think.
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#491 Re: New SE With Triode Mode KT120/150

Post by Cressy Snr »

Schematics.
Nothing much to see apart from a couple of voltages and currents changed due to the lower drop rectifiers, and a change to the cap values feeding the preamp stage. :sleepy2:
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Ray P
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#492 Re: New SE With Triode Mode KT120/150

Post by Ray P »

Looking good Steve - is it done?
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#493 Re: New SE With Triode Mode KT120/150

Post by andrew Ivimey »

Erm, the coupling cap is only 33nf- a bit weedy in the frequency dept, surely?
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.
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#494 Re: New SE With Triode Mode KT120/150

Post by Cressy Snr »

andrew Ivimey wrote: Sun Apr 25, 2021 9:32 pm Erm, the coupling cap is only 33nf- a bit weedy in the frequency dept, surely?
Corner freq is 10.6Hz with the 500K grid resistor. It’s low enough for me and the caps are teflons so the HF is lovely.
If I were brave or daft enough to go to 1M grid resistors and change to KT66 or KT77s (1M is the published max for these valves with cathode bias, below 25W dissipation) it’d be 5Hz, but I’m not brave enough, so 10Hz it is.

I took inspiration from Gordon Rankin’s Bugle 45 SET amplifier. He uses 47nF couplers with 470K grid resistors to feed his 45 output stage, giving a corner freq of 7.6Hz. I would have used 47nF too, but I didn’t have any. I did have the 33nF Russian Teflons though, so that’s what got put in.
Last edited by Cressy Snr on Sun Apr 25, 2021 10:40 pm, edited 3 times in total.
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Nick
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#495 Re: New SE With Triode Mode KT120/150

Post by Nick »

No different to 0.15uf into 100k. That would be more common and no cause of comment probably.
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