Strange bias circuit. WTF? - Page 2

Captn Dave · 30th April 2009, 05:36 AM

Of course. The cathodes are strapped. Voltage drop across the 330 R resistors would be meaningless.

A round of 10 ohm resistors for all my pentodes! I can't see any other way to do it besides using a pair of those tube socket adaptors with the internal resistor and test leads, as you mentioned.

Thanks again. Great forum here.

Captn Dave · 30th April 2009, 02:05 PM

I think the balance circuit could be adjusted by using a scope and dummy loads on the speaker taps to monitor for noise that could be added to the cathodes using a signal generator or other source of low voltage AC. The signal would be applied through a cap to protect the test equipment from the DC.

The pentodes in push pull will cancel this noise when balanced and that should be evident on the scope.

Jeb-D. · 30th April 2009, 04:34 PM

Perhaps applying a 20Hz signal (dummy loads attached) and adjusting the pot until you have the least distortion would work well.

30th April 2009, 02:05 PM	#12
Captn Dave diyAudio Member Join Date: Jun 2008	Balance without resistors I think the balance circuit could be adjusted by using a scope and dummy loads on the speaker taps to monitor for noise that could be added to the cathodes using a signal generator or other source of low voltage AC. The signal would be applied through a cap to protect the test equipment from the DC. The pentodes in push pull will cancel this noise when balanced and that should be evident on the scope.

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30th April 2009, 05:36 AM	#11
Captn Dave diyAudio Member Join Date: Jun 2008	Of course. The cathodes are strapped. Voltage drop across the 330 R resistors would be meaningless. A round of 10 ohm resistors for all my pentodes! I can't see any other way to do it besides using a pair of those tube socket adaptors with the internal resistor and test leads, as you mentioned. Thanks again. Great forum here.

30th April 2009, 04:34 PM	#13
Jeb-D. diyAudio Member Join Date: Nov 2005 Location: SoCal	Perhaps applying a 20Hz signal (dummy loads attached) and adjusting the pot until you have the least distortion would work well.

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