Audible Illusions Modulus 3 Audio Research SP-11

"bubbled edges"

To me that says you've got a microphonic tube, to do a simple test (without an oscilloscope on a test bench).

Take the lid off turn on the whole system. Turn the volume control up around loud level.

Get someone to listen close at the speakers left and right. While you flick each tube with you finger nail.

If they hear a 'bonk" out of your speaker/s then this tube is getting microphonic.

If it is really bad then it can in the worst case start a continuous feed back bong happening, and you may have to turn the volume down to stop it.

Cheers George

It is very good, but it eats tubes, as they run them hard, probably why it sound good.

Cheers George

09-24-14: Stefanovitch
It eats tubes?

Normally tubes in preamps are uncrictical? How often you did them raplce?
Stefanovitch (Threads | Answers | This Thread)

My friend would replace them every 1 to 1.5 years He would use it around 2 to 3 hours a day.
It's common knowledge that they eat tubes.

More talk on it over here.
[url]http://www.audioasylum.com/forums/amp/messages/19/196393.html[/url]

Cheers George