Jtm 45 fuse keeps blowing

[Marcelcar]

Here are some pics of the chassis

 

[Marcelcar]

I installed the Turret board. This is what my amp looks like now, will begin testing later.

 

[Chris-in-LA]

Does that blue wire go to your fuse holder or to pin 4 of your rectifier? I’m assuming that those three wires coming into the case at the top are your AC from the wall. Also I assume you connect the white wire from the board to pin 6 on the rectifier.

How is your pilot light hooked up? I think you mentioned that.

 

[Chris-in-LA]

The second set of pics came in while I was posting, ignore the comment about the blue wire.

 

[william vogel]

Does that blue wire go to your fuse holder or to pin 4 of your rectifier? I’m assuming that those three wires coming into the case at the top are your AC from the wall. Also I assume you connect the white wire from the board to pin 6 on the rectifier.
View attachment 78463
How is your pilot light hooked up? I think you mentioned that.

He had it wired to the 120 volt tap on the power transformer and run back to the fuse holder (neutral).

 

[Chris-in-LA]

He’s not running 120AC is he?

 

[Marcelcar]

Nope 240V, I'm from Germany. I'm getting about 237v from the wall so I'm running the amp with the 240v tap to get my voltages lower

 

[Trouble Free]

He’s not running 120AC is he?

120 volt pilot light

 

[Chris-in-LA]

So the 240 wall voltage and the 120 pilot light both terminate at the side of the fuse holder?

 

[Chris-in-LA]

What happens if you disconnect the 120 pilot light from the circuit? Does the fuse still blow?

 

[Trouble Free]

Yes to the common side, I know it sounds weird but I think that is correct

 

[Marcelcar]

Yes the black wire is the one from the 120v lamp and the orange wire is the common wire from the PT (the common from the PT is blue according to the documentation but the wire was too short and I had to solder an orange wire to the blue one from the PT)

Don't know if that makes any sense to you

 

[Marcelcar]

I can run the lamp directly from the 240v voltage. I got a resistor that I bought from TAD that's specifically made to run the lamp with 240v

 

[Chris-in-LA]

It was the HT fuse and happens immediately after turning of the standby switch

And the HT fuse is the one inside connected to the red/yellow center tap, right?

 

[Marcelcar]

Yes

 

[Chris-in-LA]

Yes

In that case I probably wouldn’t worry about the pilot light.

 

[Chris-in-LA]

If the voltages read within limits with only the rectifier in and the fuse blows only when power tubes are in you still might have a bad tube or a short in the tube socket.

 

[Marcelcar]

I think I've got an idea what might be wrong.

The instructions say I have to connect pin1 of the v4 and V5 socket to ground but I connected pin 8 to ground.
Both pins are bridged with a 1ohm resistor.
Could this be responsible for my problems?

 

[thetragichero]

pin 8 (cathode) must go to ground in a fixed bias amp. if the amp is to run el34 pin 1 (suppressor grid) must also be grounded (negative bias voltage may be applied to it as well but let's just keep it simple)
pin 8 -> 1 ohm bias sense resistor -> pin 1 -> ground is how i usually wire it (tube socket gives me two nice lugs to solder my resistor to)

 

[Marcelcar]

Ive got it like that now : pin 8 - 1ohm resistor - pin1 - ground.

Also I've gotten to testing my amp and with only the rectifier installed it works fine but as soon as i put the preamp tubes in I get a short.

I'm using 12ax7a-c in my preamp. Are these tubes fine?