I have a Fender Blues Jr. That has a 60 hz.hum. I know that the caps in the power supply will pass 120 hz hum if defective. I can turn up the master all the way and then turn up the volume about half way and i hear that 60 hz hum. I have replaced the red , white, purple and green wires that go the speaker output board with coaxle wires , just used the center wire without grounding the shield as there is no place to ground it. But still the hum is there. Ive tried replacing different tubes, both el84s and all 3 12ax7s. Still the hum is there it seems to be coming from the transformer. If any one on this site has an answer , please tell me . Thanks.
Check the artificial center tap resistors, R54 and R55
I think the bias supply is a half wave so that would make 60Hz hum, check capacitors C32 and C33.
If C24 is ceramic they sometimes buzz like crazy.
I think the bias supply is a half wave so that would make 60Hz hum, check capacitors C32 and C33.
If C24 is ceramic they sometimes buzz like crazy.
FYI, if you don't ground the shield, there is no benefit at all to using coaxial (shielded) cable. None.
The shield must be grounded, usually, only at one end.
The lack of a grounded shield may or may not be the source of your hum (coax without the shield grounded won't be any worse than the stock Fender unshielded cable.) But at the least, it is a waste of coaxial cable.
-Gnobuddy
My partner in crime took a crack at this amp . He did ground the shield and he also replaced two electrolytic caps , probably the ones famousmockingbird suggested. Amp seems better but still has some buzz and crackling. May be it just needs to burn in for a while. I'll keep you updated.
Last edited:
Reflow all the EL84 socket solder connections on the pcb. And or poke around with a wooden chopstick to find the cold solder joint. Like mentioned before the input Jack solder connections are always suspect.
Humbuckers or single coils (on the guitar)?
Cheap instrument cables can increase the pickup of hum (the amp just will amplify it). You don't need to go crazy here but something beyond the $10 cables often helps.
Cheap instrument cables can increase the pickup of hum (the amp just will amplify it). You don't need to go crazy here but something beyond the $10 cables often helps.
I briefly owned a Blues Jr. a few years ago. Mine would hum even with the output valves removed!
The power and output transformers were mounted too close (or in the wrong orientation) to each other, and the power transformer appeared to be inducing hum directly into the output transformer.
I couldn't find a cure for this, one of several reasons why I sold the amp on Craigslist, and moved on.
-Gnobuddy
The power and output transformers were mounted too close (or in the wrong orientation) to each other, and the power transformer appeared to be inducing hum directly into the output transformer.
I couldn't find a cure for this, one of several reasons why I sold the amp on Craigslist, and moved on.
-Gnobuddy
Actually, that is a known problem. Something that helps, at least at idle, is put an angled piece of steel sheet metal between the two transformers. It doesn't seem to act as a shield at all. Rather, by playing around with the orientation (sort of diagonally from top to bottom in space between the transformers), a cancelling field or maybe something like a humbucking field can be shaped. Once the best orientation is found the plate can be mounted or even glued in place there. Doesn't have to be grounded or touching anything else to work.
That's a clever solution. Nice!
There were several other things I didn't like about the Blues Jr., including the boxy sound (it has a nearly cubical cab, acoustically quite terrible), and the overall timbre (this was the amp that finally made me realize that I really don't like any amp with EL84 output valves in it), and the twitchy volume pot, and the wildly excessive reverb.
So I did a few mods on it - Bill M's tone control mod which was supposed to make it sound less boxy, and my own mods to reduce reverb mix level and to allow setting the EL84 bias with a trimpot.
The bias mod made it run less hot, the reverb mod helped dial in the amount of reverb I wanted, but the amp's tone was still boxy, and I still couldn't bond with it. So it went to a good home via Craigslist. It was bought by an astonishingly fleet-fingered, classically trained violinist, to use with his electric violin!
-Gnobuddy
- Status
- Not open for further replies.