Single-Ended Pentode Redux

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Cressy Snr
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#61 Re: Single-Ended Pentode Redux

Post by Cressy Snr »

I’m getting a sense that people are beginning to think I’ve lost it. :D
Anyway let’s see what today brings.
E-Linear eh! knew somebody somewhere must have done it before.
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Paul Barker
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#62 Re: Single-Ended Pentode Redux

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Im just trying to fathom the situation for the Driver. Its current feedback in the cathode which is a very small negative feedback, but thats Crowhursts description. I believe the reason we tube rolling scratch builders like it isnt just about feedback. Dont forget capacitors have a sound and microphonics. But anyway its cost is stupid high valve impedance. With a pentode that matters less, because the major influence on output impedance of the pentode is the Load resistor. Above I calced the new effective plate impedance, which went up considerably, but the actual output impedance hasnt gone up so much for same reason. But its worth keeping an eye on. But if you pass more current through the cathode resistor it becomes much smaller and the affect on plate impedance lestened greatly.

To the ECC81 surely the feedback is voltage feedback which reduces output impedance of the stage in a linear relationship (unlike the unbypassed cathode which has the multiplier of mu +1) But I have a bad feeling about the science of ultralinear influencing two stages. Am I right that they are additive? So youre making more of ultralinear, but whenever the ultralinear tap was thought up amd sized for percentage ratio didnt they set this according to their experiments in their day. You know insignificant people like Mullard et al.

But Norman doesnt help me with e linear, I dont think he envisaged it.

Lets wait and see then. Its a country mile away from my simple designs.
Last edited by Paul Barker on Tue Jan 18, 2022 8:11 am, edited 2 times in total.
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Cressy Snr
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#63 Re: Single-Ended Pentode Redux

Post by Cressy Snr »

Just googled e-linear amplifier and bah! theres loads of stuff about it. There I was thinking I’d come up with something novel. :cry: It’s even in Audioexpress. (Pete Millett) Ah well if my thinking is up with them, then I’m not as stupid as I look.
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#64 Re: Single-Ended Pentode Redux

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Cressy Snr wrote: Tue Jan 18, 2022 8:07 am Just googled e-linear amplifier and bah! theres loads of stuff about it. There I was thinking I’d come up with something novel. :cry: It’s even in Audioexpress. (Pete Millett) Ah well if my thinking is up with them, then I’m not as stupid as I look.
I know hes popular but I never enjoyed Pete Millets articles. Ive probably got the issue of a.e. But I didnt read everything. I know he grew enormously in popularity since those days, with the vehicle of the internet, and the fact he tinkers with things people want.
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#65 Re: Single-Ended Pentode Redux

Post by Cressy Snr »

OK I've configured it as E-Linear, and it's excellent.
The sound is sweet, clean, uncoloured and falls firmly into the ' this is what i want' territory. Can't grumble at all to be honest.
This is the circuit with all the voltages measured:
ELinear.png
ELinear.png (53.04 KiB) Viewed 2129 times
The simplicity is very satisfying. It reminds me of Gary Pimm's 47 push-pull in that respect (though his is a push pull pentode but he had (the slightly more complex but not that much) pentode drive (6AU6) and that's the eventual ambition with this thing, but I've had enough for now. I'll just enjoy it.
Last edited by Cressy Snr on Tue Jan 18, 2022 6:01 pm, edited 2 times in total.
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#66 Re: Single-Ended Pentode Redux

Post by Cressy Snr »

Power supply:
ElinPSU.png
ElinPSU.png (47.69 KiB) Viewed 2096 times
Not very sophisticated, but it's silent and allows great bass.
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#67 Re: Single-Ended Pentode Redux

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I've had a morning listening to the E-Linear thing and it's a keeper. It sounds absolutely superb. It is spacious, dynamic and vivid, with a beautifully detailed midrange, extended tight bass and a silky top end that extends further than I've been used to. All in all, the presence and power of this amplifier is truly fabulous. It has a consistent delivery across a wide range of music and is just a beautiful sounding thing.

The gain structure is spot on, more by luck than judgement obviously, as I just connected the existing input stage load resistors to the UL tap, so I'm well chuffed with that. If the Bates amp Paul is contemplating sounds anything like this then he's in for a real treat.

All I can say is I'm gobsmacked. It's going in a box ASAP and I fully intend to develop the topology properly by using pentode drivers, a la Pete Millett and Gary Pimm. Better power supply and the rest of the usual stuff. I only wanted a simple and cheap valve amp to use as a daily driver and I must say I have got a lot more out of it than I was expecting.

Gonna get on with some more writing now.
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#68 Re: Single-Ended Pentode Redux

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You’ve shocked me, but I’ll take that. I’ve heard Gary Pimms amp. I know the sound. I just didn’t know the circuit was that one so power to youre elbow.

Interestingly it might be better than Bates but then I don’t have a ul tap. Bates used 6SJ7 at about 1.5mA to drive 6v6.
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#69 Re: Single-Ended Pentode Redux

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Paul Barker wrote: Tue Jan 18, 2022 4:47 pm ….I’ve heard Gary Pimms amp. I know the sound. I just didn’t know the circuit was that one...
It’s not quite the same as it’s a pure pentode amp, not ultralinear, but like mine, it uses the load resistors for the first stage as the feedback resistors from the plates of the 47s. That’s where I got the idea of the combined load/feedback resistors off the UL tap from, but of course it had been thought of years ago and called E-Linear. I think he uses one of his own design CCSs as the tail of the input LTP of 6AU6s , but its ages since I’ve seen the cct.
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#70 Re: Single-Ended Pentode Redux

Post by izzy wizzy »

Douglas Picard sometimes pakprotector non de plume, has done much with E-linear uses cascode as stage 1 with mosfet top element. Of course valve would be better 😉.

Point being, pentode is probably the way to go with this. Nice result!
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#71 Re: Single-Ended Pentode Redux

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izzy wizzy wrote: Tue Jan 18, 2022 5:48 pm …Point being, pentode is probably the way to go with this…
Definitely.
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#72 Re: Single-Ended Pentode Redux

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But youve got a great result, so is it time to consolidate and enjoy that for a few weeks?
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#73 Re: Single-Ended Pentode Redux

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Paul Barker wrote: Tue Jan 18, 2022 9:19 pm But youve got a great result, so is it time to consolidate and enjoy that for a few weeks?
Oh yes, the pentode experiments will not be for a good while yet. The first task is to get the present one in a box and start enjoying it properly. It really is that good. To coin a footballing phrase, I’m over the moon.
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#74 Re: Single-Ended Pentode Redux

Post by IslandPink »

Seems to me that you took it to the amp in the second half and gave it 110% !
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#75 Re: Single-Ended Pentode Redux

Post by Cressy Snr »

Found yesterday that a simple change of rectifier to increase the HT value enables the use of KT66 and EL34 valves in the same amp for about 7W of output. They all work well. KT88 and 120 need a different output transformer so I’m not going there.
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