Ch 2 with FX loop-> sounds like in a tunnel

Guys,

I suspect its a simple tube problem. WHen you engage channel 2 AND the effects loop it sounds like its in a tunnel (mild flanger sound). You turn off the FX loop and sounds normal. Doesn't appear to affect ch 1 and 3. Is this a tube issue? If so which one?

V2 is unique to channel 2, but is on whether the loop is engaged or not. And the tubes that power the loop are also on for all channels, and whether the loop oc activate or not. (disabling the loop just shorts past the send/receive jacks).

Unless you mean setting the loop to BYPASS. But either way, no tube alone explains that behaviour. Getting a replacement and swapping them one at a time to test is a cheap process just in case though.