Fender Super 60 Red Knob Diagnosis (Blowing Fuses)

[ToneMerc]

D101-102 are 3KV rated.
The idea is to damp any flyback on the OT primary without shorting.

reddog

3KV, .250A. I have been using a 4KV, .250A though.

TM

[Stevem]

Just note that those flyback diodes 80 % of the time only protect the output tubes at the expense of the OT!
I have taken them out of every one of may amps I have ever had them in as I would much sooner loose output tubes than the OT in the amp!

[Matt D]

The problem was a shorted rectifier diode indeed! I changed out the filter caps while I was in there as well. Thanks for the spot on advice.

[camarada78]

Hi,

i'm restoring this old thread because i have the exact same problem, but i changed all rectifier diodes and both flybacks to new ones. I even changed the power tubes to no success.

The weird things:

- After each test i discharge the capacitors but noticed that only C131 and C132 had any voltage. C133 and C134 had no voltage at all.
- that led me to test L1 (choke filter - connectors BT5 and BT6, external to the circuit board):
---- L1 had no resistance, no 'bip' for shortage. it is open. It is my primary suspect (and it is smelling a little burned)

Anyone knows the value to this coil? schematic doesnt show.

thanks, have a good day

[sluckey]

If you can't find the exact replacement just use the choke meant for a Twin Reverb. Easily found and will work just fine.

However, the title of this thread indicates "BLOWING FUSES". Are you also blowing fuses? L1 being open will not blow any fuses.

[camarada78]

If you can't find the exact replacement just use the choke meant for a Twin Reverb. Easily found and will work just fine.

However, the title of this thread indicates "BLOWING FUSES". Are you also blowing fuses? L1 being open will not blow any fuses.

It was blowing fuses. But i just realized it is not blowing fuse anymore.

i started with the exact same problem as this thread. And changed the diodes as mentioned, but since i still got no sound, and saw the lack of voltage on the caps, i figured the choke problem.

I am not blowing fuses but i got no sound.

i'll order another choke and reply here.

[sluckey]

L1 didn't just burn open for no reason. Something downstream was drawing excessive current, causing fuses to blow, until the choke burned open. Likely suspects are the output tubes or C133 and/or C134.