Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Buck Webster on May 16, 2023, 09:54:04 am
-
I've got a high voltage AB763 preamp circuit going here. No stand-by. When I cold start, the voltages at the plates shoots very high and then they come back down when tubes heat up and begin to conduct. The 12AT7 reverb driver shoots up to 475v then drops to 400v when running. The main preamp plate voltages start high at over 425v and then drop back down to 265v or so when running.
Any thoughts regarding this cold start period of about 10 seconds where the voltages are very high? Risk factor for tube or reverb transformer damage?
Thanks!!
Buck
-
It shouldn’t be a problem.
-
The transient cold rating is usually double the steady-running rating. So 660V?
And yea, steady 400V is over the 12AT7's rating as a TV Tuner tube, but it will last for years.
-
^^^^^what they said;
My B+ at the 1st cap was 520v for ~~30 seconds, I took out the 500v cap and stacked 2 350V with balanced R's
since current really isn't flowing at the startup volts, things that die from current should be fine, caps die from volts, how much volts over time is a math problem I don't want to do :laugh:
-
^^^^^what they said;
My B+ at the 1st cap was 520v for ~~30 seconds, I took out the 500v cap and stacked 2 350V with balanced R's
since current really isn't flowing at the startup volts, things that die from current should be fine, caps die from volts, how much volts over time is a math problem I don't want to do :laugh:
I have 500v F&T main filters. My cold startup never seems to rise above 475v before current flows.