I built my Crack a couple of weeks ago. Everything went fine, and it sounded great. More recently I replaced the stock Phillips 6080 tube with an RCA JAN CRC 6AS7G. Even better!
I added the Speedball a couple of days ago. Everything looked good and sounded better at first, but after the amp has been on for 15 minutes or so a hum appears on the left channel. It fades in and out, but gets worse the longer the amp is left on. The left channel also picks up a lot of microphonic noise.
The thing is, the hum is only a problem with the RCA tube. The amp is dead silent with the stock tube. What confuses me is the fact that the 6AS7G worked fine prior to the speedball upgrade.
It is possible that my tube just picked a lousy time to die. What I would like to know is whether some flaw in the speedball’s construction might apparent with the 6AS7G, but not the 6080? or, alternately, could the 6AS7G have a flaw that is only audible with the speedball.
I would rather not go mucking around in my amplifier if the tube is the culprit. Any advice or insight would be very much appreciated.