• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

great start to an OTL amp. But what schematic???

I just bid on this and will probably win for $10. Looks like a great starting point for an OTL but I'm not sure what a good schematic is a good one for tube to fit those sockets.

  • Like
Reactions: 1 user


2013-04-09 9:37 pm
My OTL amp output stage can be configured to use 6c33cb or 6c19p, each has it own PCB for the output only where everything else is same. 4-5x 6c19p=1x6c33cb. 6c33cb use 24V and 6p19p use 120V for heater in series. So in schematic for Tim Mellow OTL you can replace 1x6c33c with 4-5x6p19p. With each channel 25W, you'll need much bigger power transformer with bipolar supply, +-150-170V.
Last edited:


Paid Member
2004-11-10 8:31 pm
well, as the constraint is low cost 9 pin, just get the cheapest bunch of 9-pin pentodes you can find and whatever power they give you is what you have to work with - perhaps a dedicated tweeter amp for an active 2 way set up. These days there don't seem to be many cheap tubes. What about PL82? the plate resistance is high of course but wired as a triode it maybe useable with a lowered effective plate resistance. The 6c19p has a greedy heater supply but seems a good fit.
Last edited: