Blues Jr. weird noise ?

Hi, new member here, I'm a regular over at the Unofficial Martin Forum and heard about this Forum over there. I've been playing guitar for twenty five years and just recently got an amp and electric guitar again after concentrating on Flatpicking acoustic for the last few years.


I just picked up a used Blues Jr. and I've got a question. There is a weird noise when I pick a note and the sound starts to decay I'm getting a fuzzy background sort of distortion. this is most noticable when its in the clean mode. It has I believe the original stock tube in it. I'm wondering if the tubes are bad or perhaps maybe the speaker. Any thoughts on what this might be ?

It sounds like you have phase inverter oscillation. If so, the fix is easy: re-bend one of the ribbon cables.

Here are the instructions:

Billm Cure for Phase Inverter Oscillation (http://home.comcast.net/~machrone/bjr/oscillate.htm)

Thanks Bill, How long should the amp be off before its safe to touch the ribbon to move it.

Well, I staightend out the ribbon cable and it has improved quite a bit.

There is still a slight noise but not nearly as bad as before.
This is a 2003 model might it be time for new tubes ?

PI oscillation is not usually a function of how old the tubes are, but one tube may be more prone to it than another. Try switching the 12AX7s around to see if one of them does it less when it's in V3.

When you tested the amp, did you have the back on? it needs the ground plane/shield on the back.

Yes, I had the back on when I tested it.

When looking from the back at the pre-amp tubes which is V3 and also what do the V1 and V2 power ? I'm assuming one powers the Reverb.

ASC67 - Welcome to the forum!! I don't have any helpful hints on the "noise" you're getting, but wanted to tell you these are great little amps!! I've had mine a year or so, and love it!! What a smooth, warm sound you can get out them. Hopefully, you will get the noise out of yours - and when you do - ENJOY!!!

The tubes are numbered right to left as you look at the back of the amp, so V4 and V5 are the tall ones, the EL84 output tubes.

V3 is the phase inverter, V2 is the tone stack recovery amplifier, V1 is the preamp. The reverb is driven by a solid-state op amp.

Thanks, I messed the ribbons some more and the noise seems to be gone now and there is less idle hum to the amp as well.

I'm glad it worked out!