Blues Jr all of a sudden makes a huge BUZZ. Help needed!

[Big Alex]

Hi Folks,

I got a Blues Jr for several years. It has been my main gigging amp although I don't gig so much anymore. Got JJ's on it. Gorgeous sound!

2 weeks ago I went to a recording session. Once the amp was set in the recording room I started to warm up a little. After 30 min, a loud BUZZ started (PAWWWWWWWWWWWWWWWWWW) that wouldn't go away reducing both master and volume knobs and even plugging out the cable. Turned the amp off waited a little, powered it on again and after a few chords PAWWWWWWWWWWWWW again. I Looked at the tubes and they were glowing normally. No red plating, etc.

Then I sent the amp to a very nice local tech. We managed to reproduce the problem and while the Buzz was on he touched the power tubes, move them a bit on the sockets and the buzz went away. he said I got a possible problem in the sockets solder joints or even in the tubes. He played for a while after this and the buzz didn't come back. He did a resoldering job on all sockets pins, and sprayed some contact cleaner. Then we played for about an hour with no issues. I went home certain that my Blues Jr was back on the road again.

Yesterday I decided to test it at home. Played for 3 hours with no problems. I decided to take a break and put the guitar on the stand while keeping the amp on.

I was in Kitchen when all of a sudden I heard it again PAWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW

I didn't believe!! The buzz was back! Turned it off, then turned it on again and the bus went away as for magic.

Played a little more this morning with no buzz coming back. It seems that now the amp in not as sensitive as it was before but I can't rely on it to record or gig anymore.

I heard somewhere that a bad speaker connection could possibly cause this. I compared the the plug pressure on the speaker jack against the footswitch jack and it seems the footswicht has a tigher connection.

Other than this, could it be simply a bad tube?

Thanks in advance for reading this long post and I hope somebody could shed some light on this issue.

[Kap'n]

Sounds like it's definitely in the output section, but I'd really have to see it to say more.

[Big Alex]

UPDATE

After playing several days at home with no issues I decided to give the Jr a real test at a friend´s jam.

After about 30 min playing at moderated levels (volume 3 master 5) the problem came back. I unplug the guitar cable and squeezed the power tubes on the sockets (just like the tech did) with no success.

Turn IT off and on (just like with Microsoft products) and the problem went away for a while.

More 15 min of playing the PAWWWW came back.

I Turned off the studio light and in complete darkness could inspect the power tubes. Both were red platting a little. The left one more than the right one.

Blues Jr is known to run hot on power tubes. Is this at some level normal?

Order a new set of power tubes?

Thanks in advance

[chuckocaster]

If they're a couple years old then new tubes might be in order.

[Big Alex]

Well,

The rehearsal was cancelled and only last saturday I had a chance to test drive the amp for real.

After 2 hours and a half the problem didn't appear at all. I will need a couple of additional rehearsals to be totally convinced and happy.

I replaced all tubes with a brand new JJ Kit. The amp sounds loud and good. I have asked for a late distortion kit for cooler operation. In the end the culprit was a bad tube.... :-)

If you don't hear from me in the future consider this case closed.

Once again thanks for all of the valuable advices I received from the gurus here. You guys rock.

Best Regards,