I have built a little guitar combo using some Jensen Alnicos, a 12ax7
preamp, and a thomas organ power amp. (12au7, 12ax7, a pair of 6bq5s,
and 6ca4) I know, it sounds cheesy, but it sounds really good. Or I
should say it did sound good. It has started distorting horribly and
one of the 6bq5s pulsates with the sound and almost looks like flames
in there instead of the orange glow of the other one. Is this something
that replacing the tube (or tubes) would fix?

On 8 Feb 2005 16:06:22 -0800, wrote:

I have built a little guitar combo using some Jensen Alnicos, a 12ax7
preamp, and a thomas organ power amp. (12au7, 12ax7, a pair of 6bq5s,
and 6ca4) I know, it sounds cheesy, but it sounds really good. Or I
should say it did sound good. It has started distorting horribly and
one of the 6bq5s pulsates with the sound and almost looks like flames
in there instead of the orange glow of the other one. Is this something
that replacing the tube (or tubes) would fix?

Swapping the output tubes will tell you a lot. Does the visual
symptom stay with the tube or with the socket?

Given its age, the most likely culprit is power supply electrolytics,
but you know that.

Chris Hornbeck

Chris Hornbeck wrote:

On 8 Feb 2005 16:06:22 -0800, wrote:

I have built a little guitar combo using some Jensen Alnicos, a 12ax7
preamp, and a thomas organ power amp. (12au7, 12ax7, a pair of 6bq5s,
and 6ca4) I know, it sounds cheesy, but it sounds really good. Or I
should say it did sound good. It has started distorting horribly and
one of the 6bq5s pulsates with the sound and almost looks like flames
in there instead of the orange glow of the other one. Is this something
that replacing the tube (or tubes) would fix?

Swapping the output tubes will tell you a lot. Does the visual
symptom stay with the tube or with the socket?

Given its age, the most likely culprit is power supply electrolytics,
but you know that.

Chris Hornbeck

It seems the amp is about to blow up one or two 6BQ5.

If one doesn't know how to service such an amp,
take it to a tech who does.

The electros may/may not be ok,
there may be a bad tube socket connection to the grid of a tube,
perhaps the biasing circuit has gone wrong, maybe its motorboating slowly,
and that's just what I can think of now.

Replacing tubes won't cost a fortune, but I'd have the amp checked out
before another tube or two go the same way.

Patrick Turner.