Tube voltage help

24kilo · 10th April 2006, 10:47 PM

On the Plates of the 12ax7 it's supposed to be 65 volts respectively.
But on mine it reads 63vdc pin 1 53vdc pin 6. Everything looks ok execpt the one of the 470k resistor read 460k, Other than that I can't find anything wrong. Any Help please. BTW all caps have been changed. and the Rectifier has been changed to diodes, With a bigger droping resistor R12 to get the voltage right.

anatech · 10th April 2006, 10:57 PM

Hi 24kilo,
Have you tried a new 12AX7? You have to remember that a dual triode is a pair of tubes that are individuals. They are not matched. I will assume the caps were changed with new poly types.

What exactly is the problem you are having?

-Chris

Geek · 11th April 2006, 12:35 AM

470K to 460K and 65V to 63V is moot. But at that low plate voltage, 53V can be significant.

Can you swap a couple of 12AX7's and re-measure?

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10th April 2006, 10:57 PM	#2
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi 24kilo, Have you tried a new 12AX7? You have to remember that a dual triode is a pair of tubes that are individuals. They are not matched. I will assume the caps were changed with new poly types. What exactly is the problem you are having? -Chris

11th April 2006, 12:35 AM	#3
Geek diyAudio Member Join Date: Sep 2004	470K to 460K and 65V to 63V is moot. But at that low plate voltage, 53V can be significant. Can you swap a couple of 12AX7's and re-measure?

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