An amp I just fixed was a disaster waiting to happen...

H

HamishR

Well-known member
As I have mentioned here recently I had a friend's pair of '62 Fender brown amps to repair in my workshop. The brown Super is remarkably original. It had a replaced PT which seems to be quite common but the board appears completely stock other than the electrolytics which have obviously been changed and I updated also.

But as I installed the 240V PT and connected the new 3-pin power cable I discovered that the fuse had been completely bypassed. It looked like it was connected but one end was completely disconnected, hidden by wire. So that was alarming! What kind of idiot bypasses the fuse??

All the PT grounds had been removed from the chassis solder blobs and attached to the PT mounting bolts via eyelets. Now I understand that this is a bad idea because the PT nuts can work loose so all of those connections are now back soldered to the chassis with my big heavy duty iron.

So now the amp is safe and runs even quieter than before. It's amazing how quiet an amp can be when it's grounded properly.
 
HamishR said:
As I have mentioned here recently I had a friend's pair of '62 Fender brown amps to repair in my workshop. The brown Super is remarkably original. It had a replaced PT which seems to be quite common but the board appears completely stock other than the electrolytics which have obviously been changed and I updated also.

But as I installed the 240V PT and connected the new 3-pin power cable I discovered that the fuse had been completely bypassed. It looked like it was connected but one end was completely disconnected, hidden by wire. So that was alarming! What kind of idiot bypasses the fuse??

All the PT grounds had been removed from the chassis solder blobs and attached to the PT mounting bolts via eyelets. Now I understand that this is a bad idea because the PT nuts can work loose so all of those connections are now back soldered to the chassis with my big heavy duty iron.

So now the amp is safe and runs even quieter than before. It's amazing how quiet an amp can be when it's grounded properly.
Click to expand...
The grounding scheme really makes all the difference.

Also, here's my reenactment:
"Hmm, I don't have any fuses on hand. This'll sort it for now ...."
 
HamishR said:
As I have mentioned here recently I had a friend's pair of '62 Fender brown amps to repair in my workshop. The brown Super is remarkably original. It had a replaced PT which seems to be quite common but the board appears completely stock other than the electrolytics which have obviously been changed and I updated also.

But as I installed the 240V PT and connected the new 3-pin power cable I discovered that the fuse had been completely bypassed. It looked like it was connected but one end was completely disconnected, hidden by wire. So that was alarming! What kind of idiot bypasses the fuse??

All the PT grounds had been removed from the chassis solder blobs and attached to the PT mounting bolts via eyelets. Now I understand that this is a bad idea because the PT nuts can work loose so all of those connections are now back soldered to the chassis with my big heavy duty iron.

So now the amp is safe and runs even quieter than before. It's amazing how quiet an amp can be when it's grounded properly.
Click to expand...
At one shop I worked in we had a horn repair section in the room next door. I'd sometimes have my bandmate who worked in there do Fender chassis grounds with an oxacetylene torch, but I still have an old school 300 watt iron meant for stained glass work kicking around just in case I ever take on any more repair work.

Bypassed fuses are just another of many WTF diversions for experienced repair techs, IME. Social Darwinism is alive and well, I reckon. ;)
 
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