new/first time amp build problem

[statorvane]

If you haven't installed the tubes yet, that would explain the higher than expected B+.

[rdjones]

as it is now I powered it up yesteday and nothing happened (no smoke or sound). one of the first things I am looking at is my B+ voltage seems very high for what I was expecting. my power transformer is supposed to be 120v-->290-0-290. I am measuring 120-->312-0-312.
after the rectifier I am getting ~423Vdc.

Your voltage is about 7.5% high.
This is the equivalent of running 115V primary on 123.7V.
So check your line voltage against the rated primary winding.
High line voltage is a common issue in many areas, I just measured mine now at 129.2VAC.

The 290-0-290 rating may be a loaded spec, it will run higher unloaded.
By how much depends on the degree of regulation of your transformer.
See the "AC * 1.4 = DC" thread for discussion about transformer voltages.

https://tubeamparchive.com/viewtopic.php?t=17552

423VDC is high for EL84s is you expect them to live very long.

reddog

[dju]

as it is now I powered it up yesteday and nothing happened (no smoke or sound). one of the first things I am looking at is my B+ voltage seems very high for what I was expecting. my power transformer is supposed to be 120v-->290-0-290. I am measuring 120-->312-0-312.
after the rectifier I am getting ~423Vdc.

Your voltage is about 7.5% high.
This is the equivalent of running 115V primary on 123.7V.
So check your line voltage against the rated primary winding.
High line voltage is a common issue in many areas, I just measured mine now at 129.2VAC.

The 290-0-290 rating may be a loaded spec, it will run higher unloaded.
By how much depends on the degree of regulation of your transformer.
See the "AC * 1.4 = DC" thread for discussion about transformer voltages.

https://tubeamparchive.com/viewtopic.php?t=17552

423VDC is high for EL84s is you expect them to live very long.

reddog

thanks for the reply reddog. I measured my wall outlet voltage and I got 121.9VAC. My power tranny only has primary inputs for 120V and 240V. however when i did a little math I found that if my primary was actually for 110V and it was getting the 122V instead, the math shows that I would be getting the 423VDC after the rectifier. need to get the rectified voltage down to a more usable value (TBD with help by someone with more knowledge).

an additional observation I made yesterday when trying to figure out what is going on, I was using my compu-bias probe to try and check the bias and it showed the 420v at the plate but no cathode current. I took out the probes and I noticed when I turned off the amp which had previously not made any sound, that when the switch was turned off there was sound for about 2 seconds as it faded to no sound. I could turn on the amp right after strumming a chord and there would be about 2 seconds of sound and then fade away. I could keep turining the amp on and off and I would get 2 seconds of sound before it would fade away. while I am not an expereinced amp tech, I have never heard this particular porblem mentioned. it's just one more clue to figuring out what is going on I guess.

thanks for everybody's help so far.
dj