Planning a Si rectified Clubman in a stout chassis

[Hellawatt]

Hi!

I'm planning a clubman-like build. I want to try and cram one into a stout chassis, without the rectifier tube. I remember seeing a thread on here about a 'boilermaker', a cathode biased el34 amp in a stout chassis. I really liked the idea of a compact and simple amp that would be 30 watts. I built a 15watt ef86 amp a few years ago and I love it, I just wish it was more powerful.

Anyways I bought the same transformers from the boilermaker schematic  (PT: Hammond 290CX, OT Hammond 1650) and I was thinking I would copy the power section from this schematic, and then copy the preamp from the ef86 clubman schematic.

I'm not sure which PI to copy.

Also since this will be silicon rectified, the B+ will be higher, and I'm not sure of the best way to figure out the right values for the voltage dropping resistors other than trial and error.

[Hellawatt]

Heres what I have so far

[danhei]

I think your voltages will be way too high without a tube rectifier for cathode bias. For 35 watts according to the datasheet you want 375V and a 3.4K OT.


You may want to look at this thread: https://el34world.com/Forum/index.php?topic=16494.0

[tubeswell]

2 x cathode biased EL34s will easily make 30w output power. Cathode biasing can safely run at 100% plate dissipation and in that condition, the cathode bias will have the effect of pulling the B+ down quite a bit more than fixed bias would in the same circumstances.

However, modern production EL34s are not suitable for running at the publisher’s rated Pmax IMO (unless you can find some recent NOS svetlana winged Cs). So I’d prefer to assume modern EL34s can only be ‘reliably’ run as 20w tubes (which in cathode bias push pull, should still make 30W output power).


IMHO, 400v B+ would be about right to aim for


I say all this because your schematic shows EL34s.


But if you want to run 4x EL84s in cathode bias push pull, I’d stick below 300v B+

[DummyLoad]

That Boilermaker was one of my concoctions. P-P cathode biased El34 pair with SS PS. I used Mojotone 791 (Heyboer) output transformer for the Trainwreck, 6.6K 35W. PT Mojotone 758 Vibrolux/Tremolux replacement model that fits the Stout chassis opening, I used a Fender Super Reverb choke - Plan attached.

--Pete

[bmccowan]

Hellawatt, I note that you plan to use a 100K plate resistor on v1. Is that because you think the 18K is an error, or are you seeking more gain from v1? For what it is worth, I have built two Clubman type amps. After some trial and error (its not such a bad method) I stuck with the 18K as it allows the character of the v2 pentode to come through. I used a 5879 in one amp and and a 6SH7 in the other. They were built as 6v6 amps so I can't be of much help on the dropping resistors.