807 SEP

What people are working on at the moment
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Cressy Snr
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#46 Re: 807 SEP

Unread post by Cressy Snr »

Pretty quick job done. The VR tubes shunt regulating the 7581A screen grids, are now fed by a resistor attached to the output of the regulator. Works well and the music is noticeably more free-flowing than with the CCS. Interesting.
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Paul Barker
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#47 Re: 807 SEP

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Im not sure you would hear any advantage with the 807 anyway. Its lower capacitance is for transmitting frequencies not audio, unless using AB push pull where 807 would give better higher audio frequencies.

Im a bit bombed out today from work spilling over until now. So dont inow when Ill get to lockup to see what 807 equivalents I have, I havent forgotten you and Mark are looking for dh version.
"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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Cressy Snr
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#48 Re: 807 SEP

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Deleted: Bollocks!
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Cressy Snr
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#49 Re: 807 SEP

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Paul Barker wrote: Sat Mar 04, 2023 2:26 pm
Im a bit bombed out today from work spilling over until now. So dont inow when Ill get to lockup to see what 807 equivalents I have, I havent forgotten you and Mark are looking for dh version.
Cheers Paul.
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Paul Barker
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#50 Re: 807 SEP

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Missed it anyway
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Cressy Snr
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#51 Re: 807 SEP

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Paul Barker wrote: Sat Mar 04, 2023 9:58 pm Missed it anyway
Was just waxing lyrical. Nothing of much interest.
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Paul Barker
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#52 Re: 807 SEP

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Well unlike when a woman mutters something but you dont hear it properly; its so frustrating when they wont then tell you and “it doesn’t matter” is all you get.

In youre case it doesnt matter and I domt think Ive missed anything.

I suspect women do it deliberately.

I know Im not politically correct. There are differences between the sexes.
"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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Cressy Snr
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#53 Re: 807 SEP

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Now, I’m quite embarrassed because I failed to realise that apart from the different heater current requirements, KT66s are near as dammit a plug-in replacement for 6L6. I’ve been at it for years and didn’t twig the connection until I started looking around 6L6 types the other day. So I dug out and tried a couple of used, grey-glass KTs and they bias up the same as the new production 7581As which are also a 6L6 type.
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2C783833-FFD2-4857-8D19-661E023D34CE.jpeg (103.67 KiB) Viewed 10308 times
As for the sound with these valves, now you’re talking. :)
I’ve had a love-hate relationship with these in single-ended configuration, but they seem to perform very well in this amp, giving a solid, weighty presence. The new production 7581As sound a bit lightweight in comparison.

I bought the four used KT66 from Steve a few years ago, when I was into the push-pull pentode experiments, that eventually resulted in the Barbarik project but have not really used them in anger since buying them.

I’m pretty pleased with the way they perform in this particular situation so they’ll be sticking around for a while; as long as they keep going anyway.

Also, to be honest, I could kick myself for not keeping with regulated power supplies after the 6B4G mono-blocks had performed so well. Silly.
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steve s
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#54 Re: 807 SEP

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I remember that day when we spent the afternoon valve rolling, and you took those kt66 home, they did sound nice.
Being kinkless, they where designed to be better for audio than the 6l6 types.. supposedly.

I've still got those vt75's we tried, now those where really good.

I'm sort of lacking in motivation at the moment, but I should have built an amp for those vt75's , since owston only the px4 amp has been used, everything else seems pointless.

I started another mofo before Christmas, and it's still hardly past the starting point 3 months on..
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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Cressy Snr
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#55 Re: 807 SEP

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steve s wrote: Mon Mar 06, 2023 1:49 pm I remember that day when we spent the afternoon valve rolling, and you took those kt66 home, they did sound nice.
Being kinkless, they where designed to be better for audio than the 6l6 types.. supposedly.

I've still got those vt75's we tried, now those where really good.

I'm sort of lacking in motivation at the moment, but I should have built an amp for those vt75's , since owston only the px4 amp has been used, everything else seems pointless.

I started another mofo before Christmas, and it's still hardly past the starting point 3 months on..
Aye, those VT75s were excellent sounding devices. Even used, they are not exactly cheap. The later shaped KT66 I now have, were not far behind, but there was something extra about the VT75s that made them a wonderful listen.

It’s sometimes hard to stay motivated with this stuff. I was at the end of my tether, having run out of ideas, patience and suitable bits that were in any fit condition to be used anymore. The feedback experiments started out well and ran into a brick wall of LF oscillation that I couldn't quite get shot of to my satisfaction, so I thought sod it!
In the end, all I’ve done with this is gone back to what I was up to with pentodes a few years ago, taken a proven Alex Kitic SEP circuit and thrown a load of valve-powered regulation at it, just to build something that wouldn’t need a load of brain-ache to make it work.
Last edited by Cressy Snr on Mon Mar 06, 2023 7:43 pm, edited 2 times in total.
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Paul Barker
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#56 Re: 807 SEP

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Nice development.
"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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