What do you guys think about this?

[gui_tarzan]

This is what I came up with for the layout. Obviously the remainder of the pots aren't listed, this is just the board & components.

[gingertube]

Sorry - late to the discussion.

The 50 Ohm common cathode bias resistor is what VOX used for a quad of EL84. It was actually too low for that and ran the EL84s incredibly hard.

I see that you have 150 Ohms on your layou diagram above, that is too high.

For a pair of EL84 you would normally want to double that 50 Ohm value to 100 Ohms but I'm suggesting that you use separate cathode bias resistors on each EL84 which would then mean 200 Ohms for each tube.

Given that the tubes in the VOX are run way hot, I'm going to RECOMMEND 2 operating points for you to try.
1) The standard HiFi point - use 270 Ohms 5W resistor on each tube. A 22uF bypass cap on each would be fine but feel free to try 47uF.
2) A slightly hotter (but not as hot as a VOX) operating point - use 2 of 470 Ohm 2 Watt in parallel (for 235 Ohms) on each tube. 22uF or 47uF bypass will still be fine.

You could also try 10uF bypass caps but that is getting to be a little on the light side.

For practical guidance:
I recently did a restoration of a 1963 Copper Front panel AC30 for a local guy. The entire power amp was "melted" and had to be rebuilt. With his agreement I fitted 235 Ohms (2 x 470 2 W in parallel) to each of the four EL84 and fitted 47uF Blackgate Electrolytic Bypass caps to each. He claimed it sounded better than brand new. The Blackgates were a default choice, they were the only 47uF/50V Electrolytics I had in my parts bins at the time, so maybe he got a bonus.

Cheers,
Ian

[gui_tarzan]

When you say 22uf "bypass" cap on each tube, what are you referring to? I don't recall seeing caps on any power tubes in the amps I've worked on.

[gui_tarzan]

dupe post

[JoeCon]

Jim

He's talking about a bypass cap for the cathode resistors on the EL84 tubes.

[gui_tarzan]

Oh, ok.