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The Dynaco Tube Audio Forum » Basket » MKIII W/VTA high current thru output tubes?

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1 MKIII W/VTA high current thru output tubes? on Sun Apr 19, 2009 6:31 pm

scott6058


Hello
I was curious my current thru the output tubes across the 10 ohm resistor at pins 1 & 8 is a bit high 0.58+ volts even with the pots trimmed down. I swapped some rectifier tubes and it made some difference but not much. I just purchased a new set of output tubes and they are the Russian Gold Lion type. Thanks for any help.
Regards Scott

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Bob Latino


Admin
Scott,

What you need to do is to pull the main bias resistor - the one right next to the silicon diode and replace it with a resistor of a LOWER value. I am not as familiar with the Mark III version of the VTA driver board as I am with the ST-70 version so I don't know what value the resistor is in the Mark III version and I don't know the resistor number? The resistor is right next to the 100 Mfd @ 100 volt capacitor on the bottom of the driver board

In the meantime running those tubes at .58 volts bias voltage per each KT88 is OK.

Bob

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