This Time It’s 807s

Lord Rockingham

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Another valve amp has taken up residence in the system; this time 807s in single-ended pentode mode. I’m loving the sound of this thing. It has global feedback and regulated screen grids. The two VR shunt tubes between the 807s, regulate the screens to 250V are are fed from a solid-state, constant current source.
84442808-9F91-4BFC-A398-C33BE96B9CE7.jpeg

And in the context of the full setup:
64C9E09C-2F66-4929-862F-BA6FA036CCE7.jpeg
 
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pmcuk

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Very nice! I bet it sounds good.

I'm very unsure if or how to use power tubes with top caps. I have some Mullard EL38 tubes with top caps, and they are easily the best EL34 variants I've ever heard. But I wouldn't want to sell any amp using top caps - which have around 300VDC on them - unless they were fully enclosed. And that's not easy with a tall tube. In a controlled environment tubes with top caps offer wonderful sound. You just don't know where tube amps eventually end up in their lifetimes, which is what makes me discount using them. Fully enclosed, yes go for it!
 

Lord Rockingham

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This is a dry run for a steampunk amp. If I feel it is worth continuing with, I have plans drawn up for a brass and copper chassis with some Victorian styled, earthed brass mesh covers for the 807s and a pair of round bakelite meters showing amps and volts. Should be a nice project.
OTOH It could very well end up with 6L6G or KT66. We’ll see.
 
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toprepairman

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I used to use 807's for medium wave pirate radio transmitters in the early 70's.
You could get 40Watts of RF in class C.
 

Lord Rockingham

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Aye and in audio applications, the buggers'll oscillate if you look at them the wrong way, unless given grid stoppers, screen stoppers and anode stoppers. They do sound great when got right though.
 

rabski

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Aye and in audio applications, the buggers'll oscillate if you look at them the wrong way, unless given grid stoppers, screen stoppers and anode stoppers. They do sound great when got right though.
Ah yes. I've got plenty of stuff in the parts pile that looked great on paper but actually made a world-class oscillator.
 

toprepairman

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Interesting, never had them oscillating when I didn't want them to (never and a sentence with a proposition, Lol), It's just 6L6 with a top cap, simples.
 

Lord Rockingham

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I got it a bit closer to steampunkery this afternoon, by removing the wooden trim strips in order to get a feel for the look.
IMG_0126.jpeg
Looks like it'll fly as a concept. There's a lot more to do but it should look nice.
 

bencat

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Could I ask @Lord Rockingham what you would suggest as the best valve option to drive a pair of Quad ESL 57 speakers . I have tried a Croft OTL and for various reasons that did not work . An obvious one would be Quad II which I did have a pair many years ago and were lovely but very coloured in their sound which I do not want . So any suggestions would be welcome .
 
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John (big)

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Could I ask @Lord Rockingham what you would suggest as the best valve option to drive a pair of Quad ESL 57 speakers . I have tried a Croft OTL and for various reasons that did not work . An obvious one would be Quad II which I did have a pair many years ago and were lovely but very coloured in their sound which I do not want . So any suggestions would be welcome .

I use a Rogue Atlas Magnum with my OTA Quad 57's below is a paragraph from a 6 Moons Road Tour that I read before buying https://6moons.com/audioreviews/roadtour7/roadtour3again.html it was/is a mariage made in heaven with bass

"Perhaps more than many other loudspeakers, the Quads make it difficult to generalize about amplifier performance outside of ESL-land. So take this for what it is – an informal listening session(s) of a complete system. And this system just happens to have a crew of classics - Garrard 401, REL Precedent, Stellavox SP-7 and some newcomer contenders. As is always the case at Robin's, I was treated to a wide variety of great tunes on vinyl, CD, tuner and tape. In terms of sheer musical enjoyment, this ASR/Quad rig pegged my pleasure meter like very few others have. And if the Quads have shortcomings, I didn't hear the old standards: "The Quads don't do bass." Well they do with the ASR Emitter I and the Rogue Atlas and there's no sense of dynamic drivel . Are they "the greatest hi-fi product of all time" as HiFi News anointed them? I don't know and don't really care. What I do care about is that I heard the near 50-year old Quad ESL design with amplification costing from roughly $600 to $16,000 and they consistently made some of the most engrossing and utterly captivating music I've ever heard in a home."
 
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Lord Rockingham

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Could I ask @Lord Rockingham what you would suggest as the best valve option to drive a pair of Quad ESL 57 speakers . I have tried a Croft OTL and for various reasons that did not work . An obvious one would be Quad II which I did have a pair many years ago and were lovely but very coloured in their sound which I do not want . So any suggestions would be welcome .

Hi TBH I wouldn’t know which valve amp would be good with QUAD 57s. I suspect it would need to be a decent push-pull amp, such as something from Primaluna or Icon audio. Further than that I can’t really be of much help, never having used electrostatics.
Maybe someone else will chime in.
 

rabski

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I ran 57s for a while, both a pair and a stacked pair with various amplifiers.

The amplifier matching is complex. To oversimplify, ESL57s present a complex load, with an impedance curve that changes damatically across frequencies. They are further difficult as the main load in the speaker is a transformer. The amplifier needs to be 'happy' with loads that run from near to 35 ohms around 100Hz to about 2 ohms at 15KHz.

Assuming a valve amplifier with an output transformer, this changing load is reflected by the transformer, so the actual valve (or valve pair) is similarly loaded by a wide impedance range. Push-pull designs are better suited in general, as despite the 'on paper' figures, 57s need reasonable power to work well. On the other hand, too much power is potentially damaging. Around 25-35 watts per channel is cited as ideal and I don't disagree.

For all the above reasons, against 'normal best practice' some (or even a lot of) negative feedback can be beneficial. Out of everything I tried, bought, borrowed with mine, the Radford STA15 was among the top, but needed a seriously good preamplifier to open up fully. I ran mine for a week with the Radford and a borrowed Kondo M7 and it was probably the best I ever had them sounding. The Leak Stereo 20 also performed very nicely indeed.

Surprisingly, the ones I didn't particularly like and that I thought never gelled well were Quads. The 405 and the 303 sounded flat and lifeless, and even Quad IIs never seemed to bring it all to life. Maybe some really well re-engineered variants would do the job, but it's a lot of money to experiment.

It would be interesting to revisit 57s with some of the newer valve amps around. The Icons and Prima Luna look sensible candidates, in particular those running EL34s in push-pull.
 

John (big)

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I ran 57s for a while, both a pair and a stacked pair with various amplifiers.

The amplifier matching is complex. To oversimplify, ESL57s present a complex load, with an impedance curve that changes damatically across frequencies. They are further difficult as the main load in the speaker is a transformer. The amplifier needs to be 'happy' with loads that run from near to 35 ohms around 100Hz to about 2 ohms at 15KHz.

Assuming a valve amplifier with an output transformer, this changing load is reflected by the transformer, so the actual valve (or valve pair) is similarly loaded by a wide impedance range. Push-pull designs are better suited in general, as despite the 'on paper' figures, 57s need reasonable power to work well. On the other hand, too much power is potentially damaging. Around 25-35 watts per channel is cited as ideal and I don't disagree.

For all the above reasons, against 'normal best practice' some (or even a lot of) negative feedback can be beneficial. Out of everything I tried, bought, borrowed with mine, the Radford STA15 was among the top, but needed a seriously good preamplifier to open up fully. I ran mine for a week with the Radford and a borrowed Kondo M7 and it was probably the best I ever had them sounding. The Leak Stereo 20 also performed very nicely indeed.

Surprisingly, the ones I didn't particularly like and that I thought never gelled well were Quads. The 405 and the 33 sounded flat and lifeless, and even Quad IIs never seemed to bring it all to life. Maybe some really well re-engineered variants would do the job, but it's a lot of money to experiment.

It would be interesting to revisit 57s with some of the newer valve amps around. The Icons and Prima Luna look sensible candidates, in particular those running EL34s in push-pull.

I bought the Rogue Atlas Magnum off this forum in 2013 from "sazeracrye" AKA Steve he was using the Atlas with Magies in an enormous room (penthouse) not a great match I must say, whereas with my OTA Quad 57's & supertweeters as I said in my room a marriage made in heaven. I would love to hear an ASR Emiter driving the Quads.

Rogue had modded the original Atlas for Quad users in the United States over the 40 odd years of Quad ownership I have bought or borrowed at least 25 amps including all of the above except the Kondo. At first I thought there was less bass before realising it was deeper just not flabby
or bloated. After Mark's ministrations below sounded even better.

I had to replace the 4 x KT120's I noticed the output caps looked rough Mark the Ming replaced them with Audyn Reference a 2.7uf cap would not fit under the cover a smaller value was fitted the resistor value was also changed in value to a high quality 3w 1% Mills the original were 5% so that the 3db cutoff frequency (high pass filter) was maintained at 0.8Hz. As I understand it the Audyn Reference caps have no inductance, so bypass caps were not used.

It is difficult to convey the depth of natural bass that the speakers can produce, recently someone wrote that they were stunned when an engineer played a frequency generator in to Quad 57's.
In my room I have fast articulate bass dare I say better than any Quad & amp set up I have heard.

Now back to the inhalants & pills I tested positive for covid this morning after my Mrs caught it.
 
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