Maybe helps to break it down into pre-amp and power-amp sections. Example, I see the 4 tube sections on the right as the power amp, the 4 tube sections on the left as the preamp.
There's tons of info on line for rewiring this type of amp. You might consider the venerable "fender 5e3 schematic" googl search and replicating that one - with some preamp tube sections left over on your chassis. Or try the Marshall JCM 800 https://mhuss.com/MyJCM/JCM800_2204.gif (leaving your current power amp section as is) if you're more of a lead player.
Going with one of these two circuits should sway your little amp more toward a familiar tone, which would be better than just plugging into the current "mic" input, which you could of course just do.
There's tons of info on line for rewiring this type of amp. You might consider the venerable "fender 5e3 schematic" googl search and replicating that one - with some preamp tube sections left over on your chassis. Or try the Marshall JCM 800 https://mhuss.com/MyJCM/JCM800_2204.gif (leaving your current power amp section as is) if you're more of a lead player.
Going with one of these two circuits should sway your little amp more toward a familiar tone, which would be better than just plugging into the current "mic" input, which you could of course just do.
Thank you for the reply. I appreciate it a lot.
The schematic I drew is just so I could learn the current circuit and see if any of it could be salvageable in the new configuration, which has always been the plan. After review there doesn’t seem to be anything that would carry over into a new circuit.
There’s currently three amps I’m considering cloning in this chassis since they have the same tube configurations: the Marshall 18w, the Orange AD15, or the Vox V15. The top contender is the Marshall, though with an effects loop and a master volume control rather than a tremolo. The Orange is a great sounding amp too. The Vox is more of a Marshall configuration than a classic Vox layout, since it uses a 12AX7 on the input instead of a pentode, but it has the same layout and would transfer easily.
The preamp section will definitely have to be reworked since it has two parallel inputs through both triodes that would need be redesigned for a single input with more gain stages. The cathodyne phase inverter isn’t ideal, and I’d rather use an LTP with both sides of the last triode for some additional gain. It appears there won’t be much left of the original circuit by the time I’m done, but that’s fine with me. It’ll still be the same tube configuration, which is what I was after.
Thank you again for replying to this old thread. It doesn’t seem to be interesting to most people, who would rather talk about Hammond organs I guess, lol.
The schematic I drew is just so I could learn the current circuit and see if any of it could be salvageable in the new configuration, which has always been the plan. After review there doesn’t seem to be anything that would carry over into a new circuit.
There’s currently three amps I’m considering cloning in this chassis since they have the same tube configurations: the Marshall 18w, the Orange AD15, or the Vox V15. The top contender is the Marshall, though with an effects loop and a master volume control rather than a tremolo. The Orange is a great sounding amp too. The Vox is more of a Marshall configuration than a classic Vox layout, since it uses a 12AX7 on the input instead of a pentode, but it has the same layout and would transfer easily.
The preamp section will definitely have to be reworked since it has two parallel inputs through both triodes that would need be redesigned for a single input with more gain stages. The cathodyne phase inverter isn’t ideal, and I’d rather use an LTP with both sides of the last triode for some additional gain. It appears there won’t be much left of the original circuit by the time I’m done, but that’s fine with me. It’ll still be the same tube configuration, which is what I was after.
Thank you again for replying to this old thread. It doesn’t seem to be interesting to most people, who would rather talk about Hammond organs I guess, lol.
Check out the phase inverter for a Hi-Watt. Rumored to give their amp some of its character. Easily found on line, probably with discussion. I mean, as long as you're going to toss the cathodyne, might as well build something special and with a good reputation.
I used to do this more 30+ years ago. I even wrote a paper on it, still floating around out there; http://www.geofex.com/article_folders/old2new.htm . These days, the information highway is super saturated with all kinds doing this 'n that with tube guitar amp circuits; well beyond the limited knowledge I put out, all those years ago.
An open-mic colleague suggested Uncle Doug. The guys got well over a thousand videos on the subject, plus a lot of others on YT with their videos of their take on "why this cap matters". Perhaps the lack of interest is due to their being just so much available already; its only a matter to pick something you feel is from a trustworthy source, to spend your time implementing.
Hiwatt, Fender and Marshall PI's don't differ that much. They're all LTP's, after all. Some with 12AX7's, some with 12AT7's, some with equal, some with different plate resistors. I guess thr Hiwatt sound mostly results from their Patridge output transformers, which are laid out more sophisticatedly than others.
Anyway, there's much fun in experimenting with various circuit designs 😉.
Best regards!
Thank you both for your input.
This project is still a moving target, but the “current” (as of 9:48am PST on Sunday May 11, lol) idea is to ditch the effects loop I had in mind, replace the 12AU7 with another 12AX7, then clone the preamp section of the JCM800 while keeping the EL84 power section. I’ll take a look at that Hi-Watt suggestion too. I’m still all over the place but at least my options keep narrowing down, lol.
I tested the IT voltage last night and I’m getting 388V DC from the rectifier, so I should have plenty of juice. I’m hoping to finalize the plan sometime this week so I can order some parts. This project got back-burnered a couple years ago and I just recently found the time to get it done. Finally.
Life tends to come at you fast and relentlessly.
This project is still a moving target, but the “current” (as of 9:48am PST on Sunday May 11, lol) idea is to ditch the effects loop I had in mind, replace the 12AU7 with another 12AX7, then clone the preamp section of the JCM800 while keeping the EL84 power section. I’ll take a look at that Hi-Watt suggestion too. I’m still all over the place but at least my options keep narrowing down, lol.
I tested the IT voltage last night and I’m getting 388V DC from the rectifier, so I should have plenty of juice. I’m hoping to finalize the plan sometime this week so I can order some parts. This project got back-burnered a couple years ago and I just recently found the time to get it done. Finally.
Life tends to come at you fast and relentlessly.
With 388 V supply voltage, you should opt for 7189's instead of EL84's, or the Russian 6P14P-EV's.
Best regards!
Best regards!