Previously I stated a Groove Tube 12AX7R fixed my hum problem..well it was coincidental. I removed the preamp board and inspected solder joints, check Caps for Value and ESR. What it turned out to be was the double stacked Input Jack. The signal was not being grounded when the plug was removed from the Active jack. If I played through the Passive/active jack for more gain..it hummed. Matter of fact it hummed with nothing connected. I put a guitar cable plug in the active jack to push it up then I adjusted the contact bar for more downward tension. Problem solved. Looks like this may be a weak link in the SWR amps. Hey, I don't mind...I bought it used at Guitar Center and it appears this may be why the original owner traded it in the day I bought it.