Fun with Feedback

What people are working on at the moment
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Nick
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#151 Re: Fun with Feedback

Post by Nick »

I would equally check with whats driving it, to make sure there is no DC on that. It would be broken 6sl7 that has enough grid current to damage a pot (IMHO).
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Cressy Snr
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#152 Re: Fun with Feedback

Post by Cressy Snr »

Couldn't find anything wrong with either the input stage or anything that might have been used to drive the amp.
Might have been just tired old components, well past their sell-by dates.
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#153 Re: Fun with Feedback

Post by Cressy Snr »

Lovely:
96708411-5F9D-43A4-9E1C-09895D0AD922.jpeg
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The speakers (Mission 773) may be only 85dB efficient but they sound great with the 5W Heretik amp. A happy accident of synergy? Maybe, but I’m not complaining. :)

I think that without the global feedback, the bass might have been loose, but the bass is not a problem, being tight and extended. Mids are clear and the top end is smooth, clean and detailed.
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#154 Re: Fun with Feedback

Post by Cressy Snr »

Valve amp and small Missions have been installed in the man-cave/writing room.
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CD only for now, but the amp takes the chill off the room.
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#155 Re: Fun with Feedback

Post by Cressy Snr »

Although I have solid state in the living room and it is staying there, I still like to keep my hand in with the old valve amps. Once you’re hooked on this hobby you can never leave and all that.
I’ve been experimenting with single ended pentodes again. I like pentodes you see. None of that ultralinear !
CBABBBD2-4A60-4A3B-ABA7-46AD2C8CA4AC.jpeg
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Trouble now is that because pentodes need feedback in order to perform properly, the amp is no longer committing heresy, so what now for the “Heretik” moniker? :shock: :D
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#156 Re: Fun with Feedback

Post by Cressy Snr »

Meanwhile, in the land of obsolete technology, I've scoped the circuit, tweaked the cathode resistors on the outputs and made a slight alteration to the HF compensation arrangement in the feedback loop. Nothing that spectacular needed to be done in the Fb loop, the main requirement was getting the EL34 bias right for pentode operation with 250V regulated screens (255V actual off the glow tube shunt stack.)

It acquits itself very well on all the types of music I like and has definitely rekindled my interest in valves. Did I say I liked pentodes? Ooh yes, I like pentodes. :D

Won't bother with the schematic; who cares about pentode power valves these days. May as well use transistors if you’re going to carry off like that! :lol:
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Mike H
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#157 Re: Fun with Feedback

Post by Mike H »

Image
 
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#158 Re: Fun with Feedback

Post by Cressy Snr »

Ooh look! Pentodes in the parlour (good name for an arty band) you know, just to see how it sounds with the Mission 773 floor standers like:
73E179F8-08DE-4414-A353-DF10215E41E7.jpeg
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steve s
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#159 Re: Fun with Feedback

Post by steve s »

Glad your enjoying the amp steve
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#160 Re: Fun with Feedback

Post by Cressy Snr »

steve s wrote: Fri Jan 06, 2023 10:37 pm Glad your enjoying the amp steve
Yes It’s sounding lovely.
I guess I’m just one of those oddballs who likes the sound of straight pentode operation of output valves. What I’ve got with this amp is really just a ‘classic’ early to mid 1950s circuit (6SL7 voltage amp into 6SN7 driver stage into pentode operated EL34) with HF compensated global negative feedback wrapped around it. Can’t really go wrong with a proven combination of valves.
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Paul Barker
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#161 Re: Fun with Feedback

Post by Paul Barker »

A good valve lineup.
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#162 Re: Fun with Feedback

Post by Ant »

Listened to this earlier.
This is much (much) more transparent than the earlier iteration which i heard a couple of days ago. Gets hold of the missions much better and is easier to listen to.
Better also than the nva based solid state amp that was in turn better than the earlier iteration of this amp.
The nva based one is abit wooly in the bass compared to this which i would not have expected
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ed
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#163 Re: Fun with Feedback

Post by ed »

Don't encourage him!! snigger
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#164 Re: Fun with Feedback

Post by Cressy Snr »

Circuit as it is ATM:
Heretik Pentode.png
Heretik Pentode.png (71.57 KiB) Viewed 2209 times
It works well.
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pre65
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#165 Re: Fun with Feedback

Post by pre65 »

From what Ant says you've got a good amp there Steve.

Would you agree with Ants appraisal ?
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