6B4G - The Resurrection Shuffle

[Cressy Snr]

Yes that's a lot of heat to shift.

[pre65]

Yes that's a lot of heat to shift.

Indeed.

If I has not committed myself to the 811A in A2 project I'd probably have tried your design Steve. I may still have a couple of 6S4S Russian equivalents somewhere.

[Cressy Snr]

If you built it, you'd be chuffed with it
Pair of damper diodes in a hybrid bridge to feed in the HT and you'd be laughing.

I had a bit of fun today with the circuit, discovering that if I use the 375V tap off the mains transformer, the op point of the 2A3 falls exactly on the standard RCA 2A3 spec of 250V a-k, 62.5mA current and -45V bias. So a simple move of one wire enables "normal" 2A3s to be accommodated, giving a power output of about 4W. Sound quality is unaffected. Seems there's no end to my design talents.

If I can make a changeover switch for the 450V and 375V transformer secondary taps, I'll have a true "Home/Owston" switch.

Always wanted one of those.

Currently running in standard 2A3, "Home" mode.

[IslandPink]

Nice feature ! Would like to try the old Sovtek's again some time. 'course last time I discussed the subject with James he pointed out test results showing that Sovteks are actually a fair bit away from standard 2A3 spec ... interestingly. Think the gain is a bit higher and the anode resistance higher.

[Cressy Snr]

Just a thought Phil, if you did try my design using 6S4S you'd need to back off the HT to 375V off the mains transformer secondary. With 450V and my circuit values, you'd destroy the 6S4S's pretty quick.

[Cressy Snr]

Nice feature ! Would like to try the old Sovtek's again some time. 'course last time I discussed the subject with James he pointed out test results showing that Sovteks are actually a fair bit away from standard 2A3 spec ... interestingly. Think the gain is a bit higher and the anode resistance higher.

I think the lore goes that you can also push the Sovtek/EH a bit harder than standard 2A3s.
I lust after some EML solid plate 2A3 jobbies, but I'd need a mortgage.

[simon]

I won't be pushing my Sovteks anywhere fast, except maybe the bin .

I bought some RCAs for £40 each anyway, much better

[IslandPink]

I think the lore goes that you can also push the Sovtek/EH a bit harder than standard 2A3s.
I lust after some EML solid plate 2A3 jobbies, but I'd need a mortgage.

Still haven't tried the EML mesh-plates I have upstairs

[Cressy Snr]

I bought some RCAs for £40 each anyway, much better

Still haven't tried the EML mesh-plates I have upstairs

Allright Allright, pack it in, the pair of you!

[steve s]

I bought some RCAs for £40 each anyway, much better

Still haven't tried the EML mesh-plates I have upstairs

Allright Allright, pack it in, the pair of you!

I bet px4's are better than both these valves Steve...

[pre65]

I have vague memories from when Steve (Shadow) tried a "modern" PX4 many years ago.

Or was I dreaming ?

[Cressy Snr]

I have vague memories from when Steve (Shadow) tried a "modern" PX4 many years ago.

Or was I dreaming ?

Nearly right Phil, it was a Full Music PX25 and IIRC it wasn't half bad.

I bet px4's are better than both these valves Steve...

One of these days, one of these days

[Cressy Snr]

OK, so here is the audio circuit as a standard 2A3 configuration:


All components except the 2A3 cathode resistor, are the same as the higher power 2A3-40 version.

[Cressy Snr]

And the power supply:


Last cap in the power supply has been changed from a 800uF - 385V to a 200uF - 500V

[simon]

PX4 better than a dual plate 2A3? I'm sure they are .

Still need to do that 2A3 comparison Steve. Work's been a nightmare of late with some serious problems. Just finished after a bridge strike in Hull this afternoon. I must have done about 55 hours so far this week . But we'll get around to it.