Vox AC30-6/TB blosing T500mA HT fuses

[nevetslab]

One of my steady clients sent over another one of their Vox AC30-6/TB amps that has been blowing fuses. I opened it up, finding the HT output from the rectifier tube was still wired to Pin 2 (taking current THRU the heater) instead of from Pin 8, where the Cathode is tied to the 5VAC heater. So, moved that over. Then, as that change hadn't been made, no change had been made to revise the S/B switch. It was still switching the plates of the rectifier tube. I removed those wires from the S/B Switch, joined them so the tube warms up with the DC charging up the buss caps when power is applied. Removed the switch to file out the locating 'tit' of the slotted mounting bushing of the switch, rotated the switch, then wired the switch across the the junctions of the 0.1uF coupling caps/220k bias resistors to the grids (all the 1.5k grid stop resistors parked on the tube sockets). So, this follows the discussion earlier in this thread for a Mute function while leaving the tubes powered up. Long breaks, power can be turned off, of course. While I was first getting it set up, prior to changing the S/B switch, but correcting the Cathode connection to Pin 8 from Pin 2, powering it up, it blew both the HT fuse AND the Mains fuse.

At that point, I had to drive over to the other building where CenterStaging's tube stash is, as I was out of 5AR4's, as were several vendors when looked a couple months ago. So, had to pull the chassis back out again to replace the rectifier tube. All working find now with new rectifier tube, shorting the grids together for S/B, and the HT comes up with the usual delay. I thought I had changed all of this client's AC30-6/TB amps but guess this one had been out with clients.