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Octal Power Output PCB
The octal power output PCB allows you to build a single-ended output stage using EL34, 5581, 6L6, 6V6 and other pin-compatible valves.
The valve can be fixed biased or cathode biased and there is a master volume control (option of course, just link across the pads).
With two PCBs you can make a push-pull amp -provision has been made to allow the raw HT to daisychain between the two PCBs.
The use of four PCBs to make a 100W output stage is not recommended, however, partly due to heater current constraints and partly due to non-ideal long lead connections.
Other features include:
Bias trim pot;
Input coupling cap. This isn't needed if you're also using one of my other PCBs which already has output coupling caps,
but you may need it if using this PCB on its own for special projects;
Catching diodes between grid and cathode to prevent blocking distortion (described in my book, section 4.19);
Zener diodes D7 to prevent overvoltage (e.g. at startup) and to help recovery from blocking;
Catching diodes from anode to ground to help protect against negative flyback spikes on the output transformer (use 1N4007);
Spaces for stoppers/current-sampling resistors at the cathodes and anodes (I recommend using low-power resistors here so they also act as fuses);
Pads for connecting the suppressor grid (g3) either to cathode or to the bias supply (applies to EL34 only).
The circuit in its two main configurations is shown below:
Gerber files
I no longer sell PCBs but you can find the gerber files here.
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