I recently blew the opt in my 100w Marshall. It seems the primary wires that go to the plates was grounding out to the common wire on the secondary. I replaced the opt with a known good Dagnall. The amp seemed to work and all the voltages are correcct. I started by using a Hot plate so I could pay attention to the amp as I played. Everything seemed fine. I then took the hot plate out of it and went directly into the cab. Hit one chord and I saw a spark come out of v5 (I think) and the HT fuse blew. (same symptoms as before). I had the amp open and upside down while playing so I saw the spark come from the bottome (wire side) of the socket. I'm guessing I have a bad socket but I'm not sure how to verify this, especially since it seems to only haped at full volume. I don't like this OPT much but I'd prefer not to blow it..... Any ideas?