Friday, August 10, 2012

Fender 65 Twin Reverb Reissue - Volume knob

The Fender 65 twin reverb reissue uses a smooth shaft potentiometer. The knob has a set screw that prevents the knob from spinning independent of the potentiometer shaft. Some times the shaft and knob spin independent of each other and when this happens you cannot control the switch. One might think that applying some crazy glue or similar type of glue will alleviate the problem. However, to service an amp, the pot knobs must be removed in many cases. However, to be clear, the pot "top hat's" don't need to be removed to take the chassis from the cabinet.

The switch below had a knob glued on very well, so well that when I tried to extract the knob, the shaft failed inside the potentiometer and ruined the switch.

You can see a shiny spot where Cyanoacrylate was applied

The Potentiometer is ruined (right side)

In the photo below you can see the volume potentiometer shaft extended from the its original position.

The repair isn't difficult but the parts aren't available at Radioshack and take time to procure. Time is usually what most people have little to spare. Therefore, don't glue your knobs to the pot shafts!

The picture below gives you an idea of what the inside of a Fender amp looks like when you take it apart.The picture below is of the potentiometer board with potentiometers attached. The board is attached to all the externally adjustable potentiometers for this amp (Fender Twin Reverb 65 reissue)
Fender 65 Twin Reverb reissue Amp Schematic link - 

Fender 65 Twin Reverb reissue Service manual link -

 PCB backside with clip pot soldered by factory

I used a solder sucker to remove the solder - clip is removed thereafter

Broken Fender clip potentiometer after removal 

Nice New potentiometer prior to installation

Example of improperly seated clip potentiometer

Clip potentiometer properly seated and ready for soldering

Fender clip potentiometer carefully soldered to the PCB

No solder should leak to the top side of the PCB

No solder visable on the top side - this is good!

Fender clip potentiometer is ready for chassis installation

The Fender potentiometers and PCB are ready to install into the chassis. I will now re-tube this amplifier and check and adjust the bias if needed. Burn in will be completed and then I'll check the bias again and if stabilized, I will then do a final test and finally return the amplifier to the customer. Cheers!

Updated - 12/09/14.
I've had a few requests for parts and such. So here are a couple of links that could help you if you have similar issue to the one I outlined above.

Schematic (use this link to find the part number needed)

Parts: (buy the parts from Darren - I have and it was a good experience, quick, accurate, and they even sent me some swag! :)


super_locrio said...

Hi, I'm writing because perhaps you could help me.

My twin reverb has a broken pot, Mid controller for tremolo channel. I can't find where to buy it. I don't even know which value it has (Took PCB out and it said "A250K", but i've seen and scheme of the amp and it says it's a "10K")

I'd be very grateful if you could help me with that.

Thank you.

super_locrio said...

I meant treble potentiometer, sorry.

Scott said...

Hey there, here is a link to the schematic I believe you need potentiometer R10, Fender part #0375396. I've used Darren Riley as a super reliable supplier with quick delivery, Good Luck! Scott

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