Need Help Troubleshooting

[lgehrig4]

I'm building my first amp (JTM45). I sourced the parts from a builder and the transformers are ******. I've been following the Metroamp build instructions and I just finished the amp today.

The voltage measurement were all pretty close to those in the instructions, but when I installed the power tubes and tried to bias, the V5 tube was much lower (about 15-20mA) than V4. I know that they tubes matched much close, but for the hell of it I tried two other pairs and got the same thing.

Up to that point I was biasing according to the instructions so I figured I try my Amp Head bias probe. Same thing. With these I could measure the plate voltage and V4's was .437vdc while V5's was .022vdc.

Like I said, this is my first build. What should I check first?

[Bierschinken]

Hi,

check the solder connections and the value of the resistors in the biaspart/on the socket.
Do you measure the same Ua on all tubes?

Cheers,
- Swen

[lgehrig4]

The resistors are 2W 1ohm and I tested them. I think I found the problem, but I don't know what the cause could be. All of my voltages are pretty much spot on with the exception of pin 3 of V5. The readon is -5.65, whereas the reading on pin3 of V4 is 458.

Man, I hope it's not the PT

Any suggestions?

[robert]

Hi,

check the primaries of the OT with your DMM for continuity.
Could it be possible that you have soldered the CT of the OT primary to Pin 3?

Regards

Robert