Ampeg SVT-CL hum

[Randall]

Yes, I did keep the pulls. They all tested good, except for the red plating one, which I tossed.

[boroman]

This amp is very prone to hum if you have unmatched tubes. The one you got that was redplating suggest that your set was out of balance anyway? That would cause that. Another thing is that SVT-CL hums a bit. One less, one more. In one of them I had twice hum as usually. I put new caps, cleaned grounds and checked everything ten times. Then got the preamp from another CL, swapped tubes - no difference.

The "preamp swapping" was a test because if you'd pull a jack on the back to "power amp in" you actually disconnect preamp so you can check then if the hum is going from preamp or power amp. In my case it was coming from preamp (noticeable less hum when put jack in pwrampIN) but new preamp didn't solved the problem. I get used to it :-)