The Amp Garage

Well I went ahead and revoiced the preamp and phase inverter following most but not all of the changes listed in akuster777's great post from 3/6/22. I: - halved the V1b plate load resistor at R13 to 100k - increased the V1a cathode from 1k to 1k5 - replaced R13 in the tone stack with the original 6...

Wow B Ingram, thanks very much for this incredibly detailed reply. You've given me an awful lot to chew on, which I will try to do before coming back with further comment. Again, I really appreciate it!

I’m still pulling my hair out over this amp. I'm not sure if proper protocol is to start a new thread in a situation like this but seems what's here already is the most comprehensive I can find regarding this amp so makes sense to go here but please correct me if that's not correct. I’ve tried all t...

Thanks for confirming that. I wouldn't have questioned it but for the schematic, which has a normal positive slope at the first stage then inverts it with each successive stage. But once I got to questioning it, I read somewhere that each stage is inverted if the cathode is grounded but not if both ...

Apologies for reviving such an old thread but I'm working on one of these amps and this is hands down the most informative thread I've found about them anywhere. Before attempting any of the very interesting mods described here I want to make sure there's not something more fundamental I need to ad...

Apologies for reviving such an old thread but I'm working on one of these amps and this is hands down the most informative thread I've found about them anywhere. Before attempting any of the very interesting mods described here I want to make sure there's not something more fundamental I need to add...

This is helpful, thanks. I can almost do that with just the attenuator on the signal generator. I can get TP2 to read about 200mV but it's still pretty unstable, a clear focused trace but bounces up and down a bit. I've never serviced it so probably have a bit of DC leakage where it doesn't belong. ...

It didn't occur to me I should be injecting 4mV RMS. I just figured since I'm injecting a sine wave and can't measure anything that small with DVM so have to use the scope then it must want peak to peak. But you make a good point. Not likely to be a typo, the V1A plate signal voltage looks reasonabl...

This may seem like a stupid question but do some Fender schematics have major typos or am I just stupid right now? I'm trouble shooting a Hot Rod Deville after recapping and some mild mods and trying to trace the signal with my scope. The problem I'm having is the schematic calls for a 1kHz 4.0mV in...

Sorry to hit a dead thread but thanks very much for this schematic and description of how you solved your problem. I had a very similar issue: my variac didn't start humming or anything but I was clearly not seeing the full current on the PZEM-021 and I knew when I was following the directions from ...

I am currently salvaging a large 1890 vintage pipe organ that was shipped to the west coast from Wisconsin in the mid 1980s and has been in storage ever since. The majority of its 786 pipes will be used for new builds or other organ restoration projects but all the largest pipes will likely be knock...