I'm in the midst of a ground-up rebuild of a Hammond AO-29-13 amplifier, as used in a 1962 M-100 series. I actually bought a second AO-29 amplifier, and am using the chassis, most of the tube sockets, and the percussion transformers from that, taking only the power and output transformers from my original AO-29 once I'm ready.
As part of the rebuild, I'm doing extensive before and after measurements of the performance of the amplifier, so that (a) I can see the rebuilt one is working right, and (b) see if anything changed. I thought I'd share some of my findings here.
First, here is the end-to-end frequency response of the stock amplifier (electrolytics are new), with the pedal at full volume, and the Volume Soft switch up (i.e. volume not soft):

You can clearly see the 6dB/octave roll-off at 3.5kHz, beginning gradually at about 2kHz, that Hammond designed in to minimize key click.
More to follow in later posts ...
As part of the rebuild, I'm doing extensive before and after measurements of the performance of the amplifier, so that (a) I can see the rebuilt one is working right, and (b) see if anything changed. I thought I'd share some of my findings here.
First, here is the end-to-end frequency response of the stock amplifier (electrolytics are new), with the pedal at full volume, and the Volume Soft switch up (i.e. volume not soft):
You can clearly see the 6dB/octave roll-off at 3.5kHz, beginning gradually at about 2kHz, that Hammond designed in to minimize key click.
More to follow in later posts ...
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