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 Post subject: Re: Rockola 1468 help
PostPosted: Jan Mon 29, 2018 7:02 am 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 619
Location: Dallas, TX
Yep. that's way too much ripple on pin 1. Also the DC voltage is too high.
Since pin 9 and 8 DC voltages are also high, the tube is drawing more current from the supply and that means the high pin 1 voltage isn't because there isn't enough voltage drop through the 1500 ohm resistor feeding the plates. Seems something is not right about the power supply. Doubler supplies do tend to have more ripple, so they usually have larger capacitors. Another possible problem is maybe the output stages are not doing there part to draw enough current to drop the supply voltage.
Measure the voltage coming from the power supply, that is the center tap on the output transformer primary.
EDIT: I didn't notice before that you said earlier that the voltage at the center tap was 470V instead of 420V. Also the supply voltage after the 3K was over 400V when it is supposed to be a little over 300V. The 470 might be because the silicon rectifiers have less drop that the selenium, but you should be seeing more than 100V drop across the 3K. I think you should recheck that resistor and its wiring. If too much current is drawn from a power supply the ripple will go up.

_________________
Tim
"Excellent!" I cried. "Elementary," said he. - Sherlock Holmes


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