For Nick - Yet another Pentode input amp

[James D]

Hello Nick,

I thought I would publish some more of my pentode driver based amp designs since you like them so much!

James









p.s. sorry for the lack of pentodes...

[James D]

The above post is a joke but the circuits are not - I've built and used then all and the high Gm pentode driver into DHT SE beats them all...

maybe I'm doing something wrong... please fire away with suggestions

James

[Paul Barker]

How do they scope?

[James D]

Hi Paul,

I have a scope and wave analyser and distortion analyser and meters for this, that and the other...

but I don't use them when designing or building amps unless something happens that I can't explain...

I need to get some 112s and try then into a mid voltage 211... see I do listen to you and Jonathan - but I'm not going to use a gainclone again (my tripath beats it!)

James

[Paul Barker]

OK I'll bight. I agree with you about pentode drive anyway, but those circuits.

Circuit 1 is Olsenesque so never going to sound right to me (sweeping statement but my experience so far ymmv)

Circuit 2 looks perfect, I couldn't have done it any other way, that should sound luverly. As you know I do vertually the same thing with the 112a where you have used the p2 and it's a great sound to my ears. I haven't tried p2 or lp2 though I bought some to try. Life is so short. Can it be they don't sound as good as the 112a? That would be great because being British they are short supply and expensive against cheap and plentiful. Also you didn't use a 211 as the output valve, that's where you went wrong.

3rd one is nothing like anything I would ever do so can't comment.

4th one uses great valves but is push pull. Probably uses my output transformers so should be good for a push pull amp which a lot of people seem to like. Each to his own.

I think there may have been an aikido in there somewhere?

[James D]

Paul,

Spot on as always.

1) was my take on PP triode DHT based on what I was taught as a boy by a group of retired EE who stayed with triode PP from the thirties - so same source of inspiration as Lynn.

2) Its lovely and romantic and close to my memory of Jonathans 45. The 6C4C is a russian 6B4G and therefore same family as the 45. But it isn't as neutral or incisive or dynamic (micro & macro) as C3g drive...

3) Its actually bl**dy good! Drives a CCS FR125 as monitor amp in my sons recording studio (i.e. his bedroom)

4)It is good and is destined for EggFest 3. And it does use OPTs - thank you!!! The PP is the problem - it takes some of the magic away.

You and Nick and Andrew I. have convinced me to try the 211 in SE and run it off against the PT15.

James

[Paul Barker]

well I'm just making a humble gainclone, better slew rate (though I can't see it without a scope so I'll take 47 labs word for it). Beats the pants of all that transformer distortion.

[NickG]

Well given that I am using a 5 stage amp at the moment with pentode drive, I don't know what you mean?

E810F,E810F,76,45,211

Simple eh?

PS, I think I have fixed the harsh sound of the phono, partly a grid stopper on g2, and partly by bipassing the solen coupling cap with a hoviland. Much better now. There are still some heater ferrites to add to be safe.

Remains to see how it stands up on the 9th of course.

[James D]

Well given that I am using a 5 stage amp at the moment with pentode drive, I don't know what you mean?

Nothing really it was a bit of a joke and a bit of a showoff and a bit of maybe people would like to see some different designs. I enjoyed your origonal remark in the spirit it was intended - it made me smile

I really looking forward to your hearing your phono - I have very high expectations!

[NickG]

I really looking forward to your hearing your phono - I have very high expectations!

Oh dear, I had better start a quiet spin campaign to lower peoples expectations then in advance ;-)