Mystery Amp - Take a look and see if you can help

[Howlin' Mad Mac]

Very cool project you have going there. While I'm probably loging in a little too late, I can't say for sure but your amp looks like it came out of a Hammond Tone Cabinet (fixed speaker cabinet as opposed to rotating Leslie speaker which would connect to the Amphenol connector shown on the back) which should make a decent guitar amplifier depending on your desires. In general organists didn't desire clipping or overdrive from their amps so the OT's are usually larger than needed so lots of headroom, not a lot of saturation. As for octal output tubes, Hammond amplifiers almost always use 6V6 tubes & put out about 20-25 watts. Don't know if this helps or not.

[Csquare4]

Very cool project you have going there. While I'm probably loging in a little too late, I can't say for sure but your amp looks like it came out of a Hammond Tone Cabinet (fixed speaker cabinet as opposed to rotating Leslie speaker which would connect to the Amphenol connector shown on the back) which should make a decent guitar amplifier depending on your desires. In general organists didn't desire clipping or overdrive from their amps so the OT's are usually larger than needed so lots of headroom, not a lot of saturation. As for octal output tubes, Hammond amplifiers almost always use 6V6 tubes & put out about 20-25 watts. Don't know if this helps or not.

Yes, agreed it probably came out of a tone cabinet, but it was definitely 6L6 powered. I ended up with the circuit above being modified slightly, primarily went with a little cooler bias on the output tubes, which I replaced with TS 5881 Reissues and swapped in a NOS RCA 12AY7 in V1. As it was, the tubes were running pretty hot with the 6L6's and though it sounded really good, I wasn't sure how long they would last with that kind of saturation. I got a lot more head room, now and it doesn't sound near as crunchy when hit hard, but still it really is a sweet sounding amp. Very Tweed sounding. Currently my favorite amp to play.

[Enzo]

Switching those cthode caps in and out should provide a gain boost. But do yourself a favor, add a high-value resistor across each switch contact set. I use 1 meg, because I have a lot of those, but the value is not critical. This resistor is large enough that with the switches open, the cap is still effectively out of circuit, but the resistor keeps the cap charged up to cathode voltage. That prevents a "pop" when you close the switch.

[Csquare4]

Enzo -

Thanks for commenting with the advice on the resistors. I put a 1M resistor across the two contacts on both sides of the switch and now no "pop". Not that it was very bad before, but now the only thing you hear is the mechanical click. Appreciate that. To be honest though, I can't tell much difference between the two settings, one sounds more "woofy" but I wouldn't consider it more "gainy". But either way, this amp sounds really good. I have another chassis that I got with this one - same mystery amp - that my son is working on. He is going to build a pretty straight up cathode biased Tweed Pro, so I look forward to comparing the two.

Craig