Supro Thunderbolt Gain Mod? Alternatives?

[youdevil]

I love my 1967 Harmony 525 amp which is basically a Thunderbolt with two tone controls. Rich chime, throaty roar!

However...I sure wish it had a Gain control so I could get that wonderful overdrive at lower volume!

Any suggestions for either:

Wiring something in
Adding something upstream (no stomp boxes for me thanks)
Another amp option altogether, modern OK so long as its got that simple vintage quality. (tried the Vox night train and it was too well behaved, the overdrive had that buzzy metal tone I hate...)

Sign me "hard to please"'
Chris

[Wally]

Chris, I am going to think that much of what you like about what that amp does lives in the output section....the power tubes and how they interact with the OT and speaker when the amp is pushed. IF you put in a MV, that part of the magic will go away....and you will be left with a lot of preamp gain and a 'clean' output section. Many folks who try MV amps at low volumes with a lot of preamp gain don't like the result. YMMV, but your experience with the Vox thing might indicate that you like power tube distortion.
There are those..the late KEn Fischer of Trainwreck fame was one..who believe that each stage of an amp should hit that point of distortion at the same time as the other stages in order for the amp to have that balanced richness and response. FWIW, I don't care for a big amp with a MV for most applications. If I am looking for distortion, I like a small amp that I can turn up all the way....even if it has a MV control. My Super Champs have a preamp gain, a LEad gain, and a master volume. THe amp sounds its best for me with all of those on 10. IF I want 'surf' cleans or country cleans, I won't be in the Lead function....and I might roll back the preamp gain just a bit. But...I keep the MV on 10 so that the output section is at work.

[youdevil]

Thanks for such a thoughtful and detailed reply. Makes sense. While I have you, a possibly related idea that turns up on forum posts about this exact thing...
Seems That only "half" the 12ax7 is being used, and if you want more gain you "just" wire in the other half - e g the 'spare triode.'

Sounds intriguing - and scary! In addition to mysterious. I know a fair bit about guitars but noodling around inside amps is not my thing. Ringing any bells?

[Wally]

Well, if there is an unused triode sitting there....as there is in some Bf and SF BAssman amps from the '60's...then it is an easy thing for a tech to make that triode available as another gain stage. ONe could even make a decision as to where that gain stage would go....befroe or after the tone stack.. FWIW, before any of this type of thing is done, the amp needs to be in tip-top shape...meaning that the electrolytics need to be repalced if that has not been done.
Jimmy Page put one of these to good use a long time ago..the Thunderbolt,
that is, right?

[youdevil]

Thanks again. I will bring this iPad with the amp when I visit the tech next week! And yes, Page is associated w Supros, the mythology regarding which model on which cuts rich and entertaining...

[BobbyZ]

I added a gain stage to a Wards Airline GIM 9111. (I think) Same thing an unused triod so I wired it to one of the three inputs. The one thing the extra stage does is make the amp louder. It's not like a pedal where you can get distortion at about the same volume as your clean sound.
It's cool and all but to use it you have to crank it just like any nonmaster amp.

[youdevil]

That's a really interesting point. But doesn't the increase in output lower the perceived breakup point of the speaker? In theory, that should get me farther down the field toward the goal of more distortion at a lower volume...?

(I guess this approximates whatever conversation preceded the invention of the first fuzz box!)