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Blues Amp Restoration Project Diary

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Hear an MP3 recording of the completed amp below

MP3 SOUND RECORDING OF COMPLETED AMP CLICK HERE!
(recorded with Shure SM-58 mic 6 feet away with no additional editing)
 

I replaced the bulky TAD capacitors with these yellow Mallory 150s which I hear have a slightly warmer sound than the Sprague orange drops. Although I probably should have tried the yellow Mojo Diijon caps which are suppose to be as good or even better. The smaller Sprague Atom electrolytic 25uf/25v caps work much better as a replacement for the originals and even fit the size and space of the old ones. They are about as good a cap as money can buy and will likely never need to be replaced in my lifetime. These components are vastly superior in reliability and capability to the old ones and from what I hear also contribute to great tone.

 

At first I had installed a 25uf/50v cap here as stated in the schematics but I chose later to replace it with a 50uf/50v cap just like I removed from the amp. I figure this can't hurt and seemed to be a good idea. I need to heatsink the leads on that diode before I clean up it's solder connections. I don't want to damage components with the heat and then have them fail prematurely down the road. Notice how we've removed those old resistors that someone had installed into the original configuration. I think it's important to remove any crappy modifications and changes people may have made to the amp and get it to match the intended specs.

 

I tested and cleaned the bias control pot above and replaced the resistor with a new one since this one was way out of it's tolerance range. This is a critical control pot in the operation of the amp. If it's adjusted to low the tubes will conduct current too much and reduce tube life greatly. If the biased is adjusted too high you will not get the best tone and hear crossover distortion in the tone of the amp. A non pleasant type of distortion.

Above: Here's the completed circuit board with all new capacitors, most of the resistors replaced and about 150-200 solder connections sucked dry and resoldered. I went through the wiring diagram and schematic very methodically making sure every connection was correct and good. I cleaned up the board with acetone and a brush until there was no more flux, dirt and grime around every connection. I must have removed ten pounds of excess solder. I also must have fixed a few dozen crappy mods and repairs done over the decades. The wiring was in remarkably good shape for it's age and no need to replace it.
 

I installed a whole new set of (JJ) tubes into the tight new tube sockets and added these additional Marshall style tube clips. A trick I learned from playing in clubs and traveling.

 

My son installed the speakers, soldered the lugs onto the wiring harness and assembled the speaker baffle that I had custom made by Rodgers amps. We also used yellow contact cement to attach all loose tolex covering and the paper label inside. I don't want to make this amp look brand new but I do want it to be very solid and reliable.

MP3 SOUND RECORDING OF COMPLETED AMP CLICK HERE!
(recorded with Shure SM-58 mic 6 feet away with no additional editing)

Here is the amp in all it's restored glory. I set the bias to a safe level and I'll have a professional amp shop do one other finer adjustment once I get all the tiny bugs worked out and know there are no more modifications to be made. I can say one thing. The tone is amazing and the reverb and vibrato are wonderful. It sounds better already than any time I heard it in it's past life and honestly it sounds better than any blackface I've owned before. I'm sure after about 20 hours of playing the speakers will loosen up even more. I played a 3 hour gig with it last night with great results. It breaks up nicely when the volume level reaches about 4-5 and this Gibson 335 dot guitar with it's PAF pickups really drive this amp to perfection. There is nothing like the sound this guitar and amp deliver. It's in my opinion much greater than what you hear in even BB King's sound. It's just hard to describe. Notice how the nicotine colored aging of the new grill cloth is so authentic. That was an amazingly well made baffle board I bought on Ebay for 75.00 and worth every dime. The result is about 1000.00 dollars in parts spent and maybe 20-30 hours or labor and some great quality time with my son.

CONTINUE TO PAGE 3 where I do some more modifications and recording. I put the old blue tone caps back as recommended by some experts at FDP Forum. 

HERE ARE SOME HELPFUL DOCUMENTS I USED.

TUBE ASSIGNMENTS CHEAT SHEET (something I made years ago)


 

FENDER SUPER REVERB SCHEMATIC AND WIRING DIAGRAMS


BILL OF MATERIALS
for a MOJO Replica Super Reverb Amp which is a great guide if you need recommendations for replacement parts when restoring an old amp or building a new replica from a kit.
MOJO'S PARTS LIST (adobe pdf format)

 

CONTINUE TO PAGE 3 where I do some more modifications and recording. I put the old blue tone caps back as recommended by some experts at FDP Forum. 

 

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