Just put a new Hoffman board (from Airtight garage) into my Super Reverb. It works but has a hum/buzz in the reverb/trem channel. When I pull V2 (Rev channel 12AX7) the hum goes away and the normal (V1) channel is perfect with no hum when V2 is pulled. Likewise grounding the plates (pin 6) on of V2 and V4 kills all hum. Pulling the Rev tube (V3) and trem tube (V5) has no effect on hum level... Seems that the power amp and filtering is fine and my problem lies between V2 and the PI. All voltages check out ok. Any ideas guys?