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Old 11th March 2008, 01:44 AM   #11
Tom7227 is offline Tom7227  United States
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installed a 68.2K, drove the voltage to 70.2 VDC.

Perry..your a genious !
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Old 11th March 2008, 02:08 AM   #12
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If the 68k didn't give you 80v, the transformers may have a lower ratio than the ones I've seen.

Did the voltage on pin 1 reach the voltage on pin 2?

If it's lower, the amp probably wasn't designed to operate at 80v. I'm assuming that the B+ input voltage is not below 12v and the power supplies are in good working order.
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Old 11th March 2008, 02:59 AM   #13
Tom7227 is offline Tom7227  United States
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Both were equal. 5 volts at standbye.

With the intial resistors, the voltage was 60.2 volts.

After I removed the 52.2 K resistor and put in the 68K, the voltage rose to 72 volts.
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Old 11th March 2008, 10:48 AM   #14
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It appears that the 4.75k may be out of tolerance.

When the voltage on the 4.75k resistor is 5v, the current through it should be 1.05ma.The current should be the same through the 68k resistor. That should produce 71.8 volts across the 68.2k resistor. The rail voltage should be 76.8v. (71.8+5 ). If the voltage on pin 2 is 5.1v, the regulated voltage should be 78.3v.

If the voltage on pin 2 is not exactly 5v or if the 4.75k resistor is out of tolerance, either could cause the rail voltage to vary from the calculated values.
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