Problem with a Pro Jr. NASTY Distortion!

[glp]

Been looking at it for awhile.... replaced ALL the caps in the amp - I mean every one - and swapped in and out tubes..... even jumped a new OT in.

NOTHING I do makes it any better??

Any ideas at all? I could post the voltages, if that would help?

It is a nasty distortion that only gets worse with volume. When I first heard it I thought it was Filter caps.... ugly overtones, like a second lousey note on top...... but as I said, I have replaced EVERY cap in the amp....

Stumped.....

[Enzo]

Throwing parts at it is not usually a very efficient approach.

Did you connect a diferent speaker to the amp? Try that first, just to see if it is amp or speaker.

Did you try new power tubes? or for that matter new peramp tubes? Much more likely than caps.

There are a number of test points with voltages noted on Fender's schematic, compare those to your unit.

Is there signal at BOTH power tube grids?

[52 Bill]

I know this is one of Enzo's favorites: Check the plate resistors on the driver tube.

From your description, it sounds like only one half of the output section is working. Could be a problem in the driver section. I've seen the 82K resistor fail in many of these amps.

[Enzo]

I almost mentioned that. I usually see that in things like the Hot Rod DeVille, but sure, why not?

The reason I passed it up was that in this amp, for some reason, it is 91k instead of 82k. WHy did that difference matter to me? Haven't a clue.

But I agree, it sounds like one side is absent.

[glp]

Well I'll be.....

I have had this amp laying around, open for so long. I remember when I got it in, I was sure it was a bad filter cap. Once I started there, then I figured it must be another cap passing DC...... after that - well it was the old Texas Shotgun approach.... replace 'em all!

Well tonight I tested 8 different EL84's......put the two best ones in it!

That did it!

Now I can't say I like the tone in this little bugger, not very "musical", but it is in a condition to sell now!!

I have obviously inhaled enough solder now to completely forget the first RULE in tube amp repair. CHECK THE TUBES!!

You guys were right.... I had checked all the DC voltages to the schematic and all seemed reasonable. But one of the power tubes didn't check out too well on my tester.

Maybe some one has a mod or two for this that will give it some TONE?