Motown Direct Box DIY

[CJ]

12AU7a for stage 2 is the ticket. changed the resistors a bit, strapped the OPT for 600 to compensate for the reduced gain, took out the 1 MA pot and stuck in a 250 KA with a 270 K underneath for a a 50% to 100% vol control. (the 12AU7a likes a smaller grid resistor)

the use of different resistors for plate and cathode on the 2nd stage follower results in smooth clipping on top and bottom.

freq response is 20 -20 KC , output 1 to 2 volts p-p with a 100 mv p-p input signal.

messed up schemo and waveform at clipping level (1.2 v p-p input)

 

[capacitorless]

Following with interest. I have an ancient but viable Hammond organ amp chassis to try out this design. It would be an (edit: dual channel) octal build (6SL7/6SN7/6BX7) since the chassis is 7 holes of 8 pins apiece. Two hefty chokes and a hefty power transformer.

Given that I don't have a Triad HS-52 at the moment, can I replace that with a resistor load, and run a single-ended output from the MKT-1813 for testing purposes?

(edit: like this with less dust)

 

[CJ]

Yes, that's what I did, maybe a 100 k load resistor on the output side if the cap just for the heck of it,

 

[capacitorless]

Thanks, CJ! I'll pull the chassis out of storage and order some 6BX7 and a couple of caps.