Power/volume loss after 30 seconds?

[Wallyworld]

Hey fellow Metro builders!

I love my 50 and its my #1 amp. I assembled the kit last winter and it has a LarMar MV with 50/50 preamp resisters, 0068 v1b, nos bradley kit....etc.

I have a question for this wise forum if I may? What causes a vol/head room/power loss after 30-35 seconds of operation?


After the amp is warmed up, I snap on the stand by and i get the glory and boldness and bounce than after 30secs....loss of all of that. I've repeated the experiment multiple times, same result. It still works, just isnt "right". Life is gone....still works, sounds ok_ish.. but it aint right.

I'm thinking a cap isn't working properly perhaps?


EDIT: Thanks for your reply elronhoover. A power tube was 'done'. Ive heard varying opinions on biasing and may have overworked 'em. I bought myself a pair of NOS Phillips/Mullard EL34s and, well, that takes care of that! I got them from Gregg @ Hi-test and followed his bias/testing guidelines and should get a longer life this time. The tone I'm getting is fantastic tone out of them as well!.....

Thanks!!
Wallace

[elronhoover]

Have you checked your plate and cathode voltages on your power tubes before - during - after this happens? Try that coming off standby, both with playing it (stop playing and quick check the voltages, then start playing again)and also just letting it sit idle for the 30 sec. timeframe, see if they are stable.

Dave