What amp circuit? 5U4, (2) 12AX7, (2) 6L6 "The Old Slippa"

[misterc57]

Got a hand built amp I am going to draw a schematic for and wanted to choose some schematic that may come close as a starting basis.

This amp has a clean (labelled N) and OD inputs. A volume pot for each input and one tone pot.

Maybe the person who built this amp is a member of MEF.

What known amp circuits come to mind using the titled tube line-up?

Thank you

[Chuck H]

Well one channel would seem to be "N" (normal?) and the other "OD (over drive I assume). It's a small tube compliment for both a normal and overdrive channel. I'll guess the tone control is a master tone control for both channels. This is all very different from any amp I know of with a similar tube compliment. I think you're on your own with a hand drawn schematic.

Does the amp work? With a small tube compliment and short features it wouldn't be hard to pidgeon through the circuit for repairs even without a schematic. Do you feel you need one or do you just want one? Or maybe it sounds great and you want a good format for evaluating it's mojo?

[misterc57]

Amp works great and the owner wants to know what it was based on and for me to document (make a schematic) of the circuit. He was also hoping to find out what the chassis was originally.

I have not stepped through it yet. I usually find it easier to edit an existing schematic as I have no schematic drawing software.

Thank you

[Chuck H]

I think the best you'll find would be any schematic with two preamp tubes, two octal power tubes and a rectifier. The rest of the circuit will be so different that rather than trying to make all changes and value substitutions you'd be better off spilling a bottle of white out on it. That said, I can draw five tube sockets, two transformers, three pots and five jacks pretty quickly. When I hand draw I do that previous part in ink and then use pencil to connect the dots. This allows for corrections without having to redraw those things. There's always a first, ugly draft and then at least one attempt to make a better version. I use graph paper and many copiers don't pick up the blue grid lines so copys are typically clean looking.

[glebert]

I see some big power resistors, is it cathode biased? Next question is it push-pull or SE? Two single-ended 6L6 in parallel seems weird, but it's already a weird amp. I don't know how you could get much overdrive with two 12AX7 if one of them has to be a PI. I have a homebrew amp that is two 12AX7 and one 6V6 which is basically a tweed Princeton but with the extra preamp tube to create overdrive. If the power tubes are push-pull then I would guess a 6L6 version of a tweed Deluxe but using 12AX7 instead of 12AY7 for the preamp and then cascading both triodes in that to get OD..or something.

[Pixel]

Got a hand built amp I am going to draw a schematic for and wanted to choose some schematic that may come close as a starting basis.

This amp has a clean (labelled N) and OD inputs. A volume pot for each input and one tone pot.

Maybe the person who built this amp is a member of MEF.

What known amp circuits come to mind using the titled tube line-up?

Thank you

Don't have to look too hard to see a few problems. Looks like the power cord is using a loomex connector. The fuseholder could be wired better, afaik the hot should be on the end of the holder.

[glebert]

Here's another amp (Harmony H305) that uses two 12AX7 and a pair of 6_6 power tubes. I have one of these and the second channel (input 3) gets some significant overdrive, so I guess it is possible with just one preamp tube (and second tube for PI). For what it's worth, the guys at the guitar shop where I do amp repair LOVE this amp, and swear if I made a boutique clone they could sell it for double what an original sells for, which is really dumb. I went through and checked to see if mine was stock, the only difference was the interstage coupling caps were all considerably higher capacitance than the stock, so letting more low end through which may help to the full overdrive sound.

[g1]

Here's another amp (Harmony H305) that uses two 12AX7 and a pair of 6_6 power tubes.

I found this pic to be a bit easier for viewing: https://music-electronics-forum.com/...182#post581182

[loudthud]

Not too far from a 5E3 except for the more conventional Volume controls and the attenuation on the inputs of one channel.