ah the wonders of intermittent operation.

my b-15n has started making microphonic sounds, and I don't know how I would describe it as anything other than disturbing, not low, or high shrieking...I'm assuming that it really depends on the amp/tube/filament and there is no standard microphonic sound?

I'm wondering if there's some shielding issue or perhaps one of the electrolytic caps has failed/failing. is this a push-pull amp? perhaps a failing power tube?

Dudley wrote:After three weeks of sweetness, it's back with a vengeance.

Turning down the gain reduces it a bit. Turning it up produces more of a sweep/WAH effect than just increase in the volume of the DURRR.

It sounds like you may need to have the connectors and board looked over as it may be a problem similar to what Dave-Sidca mentioned. The "wah" effect of changing the gain is because the Laney cleverly has a brightness compensation built into the gain control.

Madlee, have you tried carefully tapping the preamp valves with a rubber-tipped pencil while the amp is on? Sometimes you can pick out very microphonic valves from doing this.

Rodabod wrote:
Madlee, have you tried carefully tapping the preamp valves with a rubber-tipped pencil while the amp is on? Sometimes you can pick out very microphonic valves from doing this.

oops. I may have misled you to think I was talking about my amp. I meant to direct my comments at the laney. there's nothing electronically wrong with my b-15n. I think the problem is a result of the original gasket material has compressed to almost paper thin thickness.

I've read that the non mil-spec 6SL7s are very prone to microphonics, so I've been looking for (3) 6SL7-WGTs for just this reason. nonetheless, I blew an ebay auction for 5 NOS sylvania brown base WGTs for like $25. dumb.

I did tap the preamp tubes and they do make a noise (tap noise that increases in volume to a bang sound the harder I strike). Perhaps they are worn too, since the tubes are all original, but as long as the amp isn't too loud to vibrate the head, it sounds fine and is quiet with no hum. maybe I'll just stick some foam under the lid to deal with it for the time being.