The bright channel breaks up around 2, the normal channel around 4. I suppose I can roll some tubes in the preamp, but I’ll save that for once it’s stable. So far, it has only blown fuses with power tubes installed.
I haven’t checked my JTM45 with Metrospec iron but your initial b+ is about 100 volts higher than the manual shows, which is about 400v, not 500v. Didn’t you get that Merren PT from a forum member? Maybe it’s not the right PT.On Thursday night, I went to fire it back up to measure voltages. I took it off of standby and about a minute later, the mains fuse blew. Had a pretty full plate the last few days, so I put it away.
This evening, I went back at it. First, I pulled up the schematic and buzzed out the entire amp from input jacks to power supply, expecting to find an issue that would jump out. Everything was a spot on match and grounds were all solid. So I moved on. As @neikeel suggested, I removed the output tubes to measure voltages and recorded everything in the chart below. Then I powered off, put the output tubes back in, and powered on again. As soon as I hit the standby switch, I heard a loud hum through the cab and the HT fuse blew. For grins, I swapped the GZ34 for another I have on hand and the exact same thing happened.
I'm at a bit of a loss here, but if the chart triggers anything that you all think is worth checking out please do let me know. TIA.
PT is correct and voltages have all settled down now. I didn’t record the exact B+ but it was somewhere right around 450. Higher than the metro but the same as what Neil and others reported on either Merren or original Drake. I’ve still got another pair of KT66 now to try, I’ll pop them in and take some measurements shortly.
Haha ok, I’ll have to swing by the hardware store first. I’m taking it out for a real world test at church this weekend.
