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Old 13th April 2012, 06:00 PM   #11
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andrew; 1000 vdc. 750 vac
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Old 13th April 2012, 06:06 PM   #12
MelB is offline MelB  Canada
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Cowboy, leave the standby OFF. Measure the voltage on pin 5 of the power tube (6L6). Try to get that voltage up over -40 volts. There should be a pot to adjust.
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Old 13th April 2012, 06:51 PM   #13
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the ab165 circut uses a pot to minomize hum it only bias's one tube, right now i have -30 vdc coming off the board
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Old 13th April 2012, 07:03 PM   #14
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the best i can get on pin 5 is 29.9 on one, 24.9 on other 6l6. one is adjustable the other is not. how do i raise the voltage on both of them?
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Old 13th April 2012, 07:38 PM   #15
TheGimp is offline TheGimp  United States
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Yes.
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Old 13th April 2012, 07:44 PM   #16
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the voltages i quoted should have been -24.9 and -29.9 at pin 5 sorry. would this indicate a bad resister or capacitor.

Last edited by cowboy 1; 13th April 2012 at 07:54 PM.
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Old 13th April 2012, 08:21 PM   #17
TheGimp is offline TheGimp  United States
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Measure them for AC voltage. It should be in the very low mV range. If not you may have a cap problem.

If the AC voltage is in the low mV range, then I would expect the problem to be in the resistors.
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Old 13th April 2012, 09:40 PM   #18
MelB is offline MelB  Canada
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Is the resistor going to ground in the bias circuit measuring 15K?
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Old 13th April 2012, 09:41 PM   #19
MelB is offline MelB  Canada
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Or is the cap in backwards there? The positive goes to ground in the bias.
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Old 14th April 2012, 03:46 AM   #20
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the bias board resister is 470 ohm 1watt off 1 diode, cap is 50uf-50v off same line to + ground. both are new.
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