Standby on - good, standby off - mains fuse blows

[kerry_okie]

I'm putting one of George's JTM45 boards in an old Traynor Bassmaster using the original Hammond trannys. I'm also using a Weber Copper Cap (WZ34) in the rectifier socket.

The power tranny is a Hammond 378X. It's a little hotter than than a typical JTM45 tranny. I'm getting 430V at pins 4 & 6 on the rectifier socket, and 387V DC out of the Copper Cap to the standby switch.

Here's where I think the wheels are coming off. From the standby switch, I'm going to one side of the 32X32 filter cap, where it joins one side of the choke and the red wire to the output tranny. The other side of the filter cap has the wire to the other side of the choke, the yellow wire going to pin 6 on the output sockets, and one wire going to the 10K resistor on the board. On the 16X16 cap, one side is going to the opposite end of the 10K resistor on the board, and the other side goes to pin 1 on V2.

I put the preamp tubes in to check voltages. When I flipped the standby switch, the amp started making a weird clicking sound and blew the mains fuse. Replaced the fuse, pulled the preamp tubes out, and tried again with the tubes out - and the mains fuse blew again.

Where should I start looking to chase this down?

-- Kerry --

[Guest]

Try replacing the rectifier tube

[kerry_okie]

The rectifier "tube" is a Weber Copper cap. Unless I'm missing something in Weber's literature, there's nothing in them that can blow.

-- kerry --

[ScottW]

Here's where I think the wheels are coming off. From the standby switch, I'm going to one side of the 32X32 filter cap, where it joins one side of the choke and the red wire to the output tranny. The other side of the filter cap has the wire to the other side of the choke, the yellow wire going to pin 6 on the output sockets, and one wire going to the 10K resistor on the board. On the 16X16 cap, one side is going to the opposite end of the 10K resistor on the board, and the other side goes to pin 1 on V2.

-- Kerry --

Wait, you have the caps wired wrong. Yes, the B+ from the standby switch goes to the positive side of the first cap where it meets the center tap of the OT and the first wire from the choke. The negative side of this cap MUST go directly to ground. Same with the negative side of the second cap, it must be grounded.

While you're in there, it couldn't hurt to check those caps for damage cuz they were wired in a way that might have cooked them. Hope this helps.