5E3 with EL34s

[KingCameron]

Guys,
I have been working on 5E3 build with an EL34 output stage (fed from a Bandmaster OT) and the fixed-adjustable bias supply from the 6G3.
Attached is my personal schematic to show you where I am at.
I have built the amp and amp getting some sound in the output, but it is gravely and takes a lot of volume to hear the guitar at all.

I am curious to know if I have enough capacitance in my power supply?

...actually any input at all...

This has been one of those "back of the bench" pet projects that I'd like to get wrapped up.

If one of you suppa stars an take a peek at my schematic and let me know your thoughts, I'd be mighty happy

Thanks,
KingCameron

[MWJB]

Plate voltage is a bit low for a EL34 amp.

I'd go with 0.02uf coupling caps at V1 plates, smaller bypass cap at V2, pin 3, sat 1-5uf?

Your bias supply looks a bit odd. You may have drawn it wrong? If you do not have a bias winding, the supply should be tapped from one of the rectifier secondaries, from the PT to the recto tube, NOT from the B+ supply. Look at a push pull Princeton bias supply.

You want a filter cap to ground right after the bias diode (25-100uf/100v). You have -40v, so why only a 25v cap? A 50K trim pot should be ample, wire it like a variable resistor, then add a fixed resistor between trim pot ground, of a value that stops you shoving too much current through the power tubes.

66uf should be plenty adequate as B+ filter.

Some pics of the build might be useful, when looking at the schem, we are only looking at what you have drawn, not what you have built.

[booj]

yea. it looks like your bias is hosed. also 96uf is a bit much for the rectifier. 40 or maybe 60 at most.

[tubeswell]

Hiya Cameron

+1 what MWJB said about the bias supply feed - (you want a VAC source to rectify into a steady -ve DC voltage - you can't do that from a DC supply, which is what the B+ is). Also find some 63V (or better still, 100V) caps for that location.

You also should have either a 50mA - 90mA HT choke (CLC filter), or a 1k - 5k 5W resistor (CRC filter) between the OT primary B+ supply filter cap and the screen supply filter cap, for the Pii filter. TR2 @ 90mA where you've drawn it probably isn't sufficient for 2 x EL34s & 2 pre-amp tubes - it would need to handle hundreds of mA if it is put before the OT primary. Otherwise, move it and make it into your CLC filter as described above.

You also need a further supply resistor in the B+ line between your 30uF screen node cap and your 16uF PI node cap. Try 5k, 10k, 22k or 27k to see which gives you the right voltage on the PI/pre-amp plate(s).

Is your V1 cathode resistor wired to both cathodes in that stage?

Your parallel 32uF caps at the OT primary only give you a 16uF reservoir for your rectifier, which is not much for a GZ34. You might to better with 40uF - 60uF there (60uF maximum for a GZ34).

Otherwise, if you haven't got enough juice with the GZ34 once you've made those changes, then you could use SS rectification with the amp (2-3 x 1N4007s in series on each side of the HT secondary, with .01uF 3kV snubber caps - 1 x in parallel with each diode)

[MWJB]

"Your parallel 32uF caps at the OT primary only give you a 16uF reservoir for your rectifier, " Parallel 32uf caps will give 64uf, but as Tubeswell sugests the choke could be moved to between the OT centre tap & he screen supply. If you keep the choke as an input filter (e.g. before the OT centre tap) 20uf at either side will be fine (noting Tubeswell's observations about current handling requirements).

[tubeswell]

"Your parallel 32uF caps at the OT primary only give you a 16uF reservoir for your rectifier, " Parallel 32uf caps will give 64uf,

Oops! of course they do. (Okay so it was 12:30am here when I posted that )

[loudthud]

The cap feeding Vol2 is going to B+ instead of the plate of the 12AY7.