#169014  by TI4-1009
 
Good luck- let us know what you find out.

I keep looking at the jack added to the back expecting it to be a "preamp out", but it looks like it's just another extension speaker jack? Looks like it's just connected to the jack next to it.

And I still can't figure out how you can use the amp without a rectifier :?: :?: :?: The amp needs DC power to work! Must be more there than meets the eye....
 #169017  by JimmyFitz
 
I agree - it appears to be a speaker extension with a resistor on it for some reason.

As for the rectifier, I've come across some YouTube videos and websites where people talk about replacing the rectifier tube with a pair of diodes wired the same way as in my amp. It looks like that's what was done here. That's the only explanation, really.

The diodes look weird, though. They're ball-shaped and have colored stripes on them like a resistor. I can't find any diodes online that look similar, but I assume that's because they are 40+ years old. I wish I could get a better look at them, but they're covered by that clear tubing and I'd have to desolder them to safely remove the tubing.

I guess if Jerry or Bobby was looking for the crispiest, clearest tone, he'd have wanted a solid state rectifier to eliminate any rectifier tube sag. Or perhaps it was modded because the diodes are more reliable than a tube.
 #169020  by TI4-1009
 
Ah, OK, so that's what's up with that...."thing" that's over the rectifier socket! Could well be, never seen that before!
 #169024  by JimmyFitz
 
It sounds like a Deluxe Reverb on steroids. Almost like a Roland Jazz Chorus. Very very loud and clean clean clean. It is hard to use in a band situation because the volume is so touchy. The highs are very crisp, and now I'm realizing that maybe that's due to the mods. I've only played it maybe 10 times in the last 20 years because it's way too loud for the house and I've been too nervous about it to gig with it.
 #173677  by JimmyFitz
 
I wanted to restore the amp and make it reliable and playable, so I replaced all the old capacitors (some were leaking) and removed the rectifier mod for closer inspection. When I removed the clear tubing that surrounds the mod, I saw that the old diodes were burned and melted. I don't know how the amp was able to function, but I imagine it wasn't operating at its best. I plugged a recifier tube into the socket, and now, with new tubes and caps, it sounds amazing and is more reliable that my other amps that are 30 years newer.

Thanks everyone for your help!