Blues Jr Distorts At Low Volumes

Elias Graves

Elias Graves

Common misfit
How do I troubleshoot this?

Three years old. Been played many many hours by my son. Lots of it at fairly high volumes. :grin:

Tubes? Speaker?

EG
 
Ummm....not clean?

Definitely does not sound like an overdrive breakup. Kinda fizzy sounding maybe.
Volume at 1, master at 1, fizzola. You can still hear the guitar and all...it's not fizzing just sitting there. But hit a note and it's just distorted. Sounds kinda like bad clipping from a SS amp or something.

EG
 
Elias Graves said:
Ummm....not clean?

Definitely does not sound like an overdrive breakup. Kinda fizzy sounding maybe.
Volume at 1, master at 1, fizzola. You can still hear the guitar and all...it's not fizzing just sitting there. But hit a note and it's just distorted. Sounds kinda like bad clipping from a SS amp or something.

EG
Click to expand...

could be a tube. could be something worse. take it to a tech.
 
The BJr has 3 12ax7a's in the preamp & phase inverter. Those are cheap enough to buy at least one and try swapping each one out. Other than that, it could be something simple like a cracked solder joint or blown cap, but it takes someone who knows what they're doing to find it without electrocution.

By the way, the BJr does have ss in the "Fat" circuit and the reverb circuit drivers.
 
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Swapping out the tubes is easy not very expensive. It would be my first step before taking it to a tech.
 
I'd go to the tech first. When mine was acting up, I considered buying tubes first but it would have been close to $100 for a complete set and I didnt want to spend it if that wasnt the problem. I took it to the tech who fixed all of the solder issues and it was $80. I still might replace the tubes but I'll do the pre amp first and the power tubes later.

If a speaker were that bad, the damage would be visible, no?

It definitely sounds like something let go and you have an amp guy, right?
 
Yeah, I got hooked up with a local guy last week when my kid's other amp (Peavey Vypyr) crapped out. He took care of that under warranty.
I got to talking to him and offered to trade him a couple of old console radios taking up space for some mods to my Champ. I'll take it to him.
A complete tube swap will cost me $65 or better. I'd rather not spend that if not necessary. It sounded fine before, so I'm not looking to swap if not needed.

EG
 
Johnny N. said:
If a speaker were that bad, the damage would be visible, no?
Click to expand...


Not neccessarily.

The voice coil of the speaker is basically a coil of wire that slides down into a channel in the magnet of the speaker. Tolerance between the coil and the magnet is very, very tight. I'm talking .01s if not .001s of an inch. When you blow a voice coil, what happens is a spot on the coil swells up and rubs on the side of the magnet, creating the scratchy distortion you associate with a blown speaker.

You can't see the damage unless you can pull the magnet off the back of the speaker (which isn't always easy).

You can test if it's the speaker though by gently pushing on it and listening and feeling for the scratchiness.

I'm in the camp of people who in this case would buy one preamp tube and swap it into all positions to see if that fixes it. $10 or so is all it'll cost you if it's not.

If it's a power tube, you'll need to replace both of them (the BJ does have 2, right?). If it's not tube, it's probably a capacitor.
 
If you want pop the back off (don't touch nothin'!), I think you can see the filter caps and if they look like this (note unwelcome yellow foamy stuff) they need to be replaced:

vented_cap.jpg
 
k4df4l said:
That's why I always have a spare set around.....tubes are easy to swap and usually the cause of many tube amp ills.
Click to expand...

+1

Even a very cheap set just for trouble shooting. Usually when I get a tube amp, I replace the tubes with a flavor I like, then I keep the original tubes for just such an emergency.
 
I've bought most of my tube amps used and had no idea how old the tubes were when I bought them, so one of the first things I usually do is retube it and save the old tubes as spares.
 
I suspected tubes, however, I'm an idiot with amps, the thing is three years old and never been looked at, so I figured I'd let an expert check it out just to make sure there wasn't something bigger wrong with it.

Now, to locate appropriate toobz.
The boy generally likes the amp as it is. I'll probably just go get som JJs or something. They seem to work well.

EG
 
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