ECL82 SE

[simon]

I've been feeling like building an amp recently as I haven't built one in a very long time, an itch to be scratched. Spurred on by Steve's 6V6 SE build I thought about building another 6EM7 amp, but when I looked for the schematic on the hard drive I found James' ECL82 SE - he must have posted this maybe 17 or 18 years ago . James spoke highly of it and I bought a few bits but never got around to it. So this is the one I'm going to build. Don't know what I'll do with it but that's not the point.
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ECL82SE_trioded_2.GIF (4.5 KiB) Viewed 28276 times

[simon]

A few things that strike me.

Low HT of 180V! I don't have any small mains trafos but a 50VA 230V isolation transformer might do the job.

I bought 4 I think ECL82s. They're £30 each now, though PCL82s with their unloved 16V heaters are still £7.50.

Each channel has 3 150H 8mA chokes, two as anode load for the triode driver and a third as grid choke for the output pentode. I bought 4 of the Hammond chokes, not sure why not 6, but I have another pair of small chokes I'll investigate for suitability.

I don't think I have anything suitable for the 10H chokes. I might have some large AE 6 chamber jobs - their DCR will be a lot lower I suspect, but as the current through the triode is at a guess 2 or 3mA the difference in voltage drop will be negligible. The higher DCR might have been beneficial potentially for the power supply, difficult to say without knowing the power supply.

I'm tempted by a diode of some sort instead of the triode's cathode resistor and bypass cap, I'm guessing the cathode is at something like 0.7V or thereabouts.

For the power supply I'm tempted by a shunt reg, just because I have a Salas SSHV2 board spare and one would do both channels. Otherwise a simple choke input.

Right, I need to fire up PSUD to see what I can get out of a 230V secondary.

[pre65]

I built this very amp many years ago.

The PSU was in an old WAD chassis which I got from our Mike, that might have been our first meeting.

I've still got the PSU, in slightly altered form. Looking forward with interest to see how you get on Simon.

PS I looked into my Photobucket site for old pictures but it's been deactivated as I would not pay them any money.

[simon]

Don't blame you, I won't pay Photobucket either!

What did you think of the amp?

[simon]

It looks like a 230V isolation trafo with choke input and SS bridge would give around 180V. Perhaps that's why the HT is 180V?!
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PSUD Choke Input 180V.png (169.85 KiB) Viewed 28255 times

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For shunt reg, the reg needs a minimum of 20V, so a small first cap of around 3uF would probably do it.
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PSUD Choke Input 220V.png (185.85 KiB) Viewed 28255 times

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Are there any issues using isolation trafos?

Something like one of these?
https://www.mouser.co.uk/ProductDetail/ ... v27Q%3D%3D

https://www.mouser.co.uk/ProductDetail/ ... pNSQ%3D%3D

[andrew Ivimey]

Hi Simon, I did what I called The Doddington Special - he was charmed - Total gent.

In those days I knew a chap in Hong Kong who wound pretty much anything so I got what Mr D ordered. I vaguely remember bringing it to Witham.( when I dropped my wallet into a speaker cabinet I was passing on to T'other Andrew It was lovely but I remember that it showed up the difference between Mullards and Soviet ones hugely, surprisingly. Only one giitar amp manufacturer I know ( Carr) uses ecl 82 in pp and its begging to be copied. SE is a natural - oh there was the thingie amp where the pentode acted as a ccs under a 45, the triode as input. That was brilliant. Don't be afraid of pcl or indeed, isn't there a 30 volt heater variant too. They are wonderful.

I do go on I'm afraid.

[Nick]

They should be fine.

[simon]

We love you Andrew, and your eloquent verbosity. It is a rare pleasure in a sea of anger and prejudice. (I meant the Internet in general before peeps get excited).

Thanks Nick.

[pre65]

It is a rare pleasure in a sea of anger and prejudice.

Simon, the one I built was so long ago I can't begin to describe the sound quality.

[simon]

I've never built that 45 amp with CCS you mention Andrew, and you've spoken in glowing terms. I love the Bugle I have now which I use above c300Hz, but I should try it really.

[simon]

Hmmm, I've lost my Sound Practices CD so don't have a copy of that 45 CCS circuit, well that's probably a good thing.

[Mike H]

I built this very amp many years ago.

The PSU was in an old WAD chassis which I got from our Mike, that might have been our first meeting.

Yes it was! You also had two big potted toroids, but maybe another day...


Nowt wrong with ECL82, however (sorry) I'd want to run the pentode as a pentode.

[pre65]

I built this very amp many years ago.

The PSU was in an old WAD chassis which I got from our Mike, that might have been our first meeting.

Yes it was! You also had two big potted toroids, but maybe another day...

No, same day, the potted toroids were used on that chassis to make the PSU, dual mono it was.

[Mike H]

Appendix - ECL82 in push-pull might be interesting too.

[andrew Ivimey]

WAD did a lively design and Neal's your man for that.