CP103 voltage question
Posted: Thu Nov 07, 2013 11:11 am
This question is mostly for Clayton, but everyone feel free to chime in...
I built a CP103 clone based on Clayton's original '69 non-Who CP103. As all of you probably know, this model was originally Dave Reeves' design for Sound City (aka SC One Hundred). Since Townshend liked them so much, the design was carried over into the Hiwatt line, but only a few amps were made, custom built for The Who. However, it appears a few non-Who amps were also made.
My question is about the voltages at various points inside the amp. The Sound City and later CP103 are all very similar, but with a few minor differences, mostly in the layout of the B+ line and the value of decoupling/voltage drop resistors along that line.
Sound City: 6k8 between output screen grids and the phase inverter/master volume tubes, 22k between PI/MV and EQ tube, then 47k between EQ tube and the two input tubes
'69 CP103: 1k between output tube screen grids and PI/MV, 22k between PI/MV and EQ, 22k between EQ and input stage
'70 and on CP103: 1k between output screen grids and PI, 10k between PI and EQ, 22k between EQ and input/master volume stage (shared)
My question to Clayton is: what are the voltages in your '69 amp along the various points in the B+ line? For reference, what is the heater voltage when taking those readings?
I started out with pure '69 specs, but have ended up with Sound City specs for the B+ line, but with 82k/91k PI plate resistors (stock for late '69/early '70 and on). Pure '69 specs to me sound the cleanest and stiffest, those little mods seem to make the amp a little warmer and break up a little more, but still cleans up amazingly well. I do however have slightly high voltage out of the wall, which yields higher voltages at all points in my amp, so for reference it would be most interesting to hear what your amp has.
I built a CP103 clone based on Clayton's original '69 non-Who CP103. As all of you probably know, this model was originally Dave Reeves' design for Sound City (aka SC One Hundred). Since Townshend liked them so much, the design was carried over into the Hiwatt line, but only a few amps were made, custom built for The Who. However, it appears a few non-Who amps were also made.
My question is about the voltages at various points inside the amp. The Sound City and later CP103 are all very similar, but with a few minor differences, mostly in the layout of the B+ line and the value of decoupling/voltage drop resistors along that line.
Sound City: 6k8 between output screen grids and the phase inverter/master volume tubes, 22k between PI/MV and EQ tube, then 47k between EQ tube and the two input tubes
'69 CP103: 1k between output tube screen grids and PI/MV, 22k between PI/MV and EQ, 22k between EQ and input stage
'70 and on CP103: 1k between output screen grids and PI, 10k between PI and EQ, 22k between EQ and input/master volume stage (shared)
My question to Clayton is: what are the voltages in your '69 amp along the various points in the B+ line? For reference, what is the heater voltage when taking those readings?
I started out with pure '69 specs, but have ended up with Sound City specs for the B+ line, but with 82k/91k PI plate resistors (stock for late '69/early '70 and on). Pure '69 specs to me sound the cleanest and stiffest, those little mods seem to make the amp a little warmer and break up a little more, but still cleans up amazingly well. I do however have slightly high voltage out of the wall, which yields higher voltages at all points in my amp, so for reference it would be most interesting to hear what your amp has.