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ampage archive
Vintage threads from the first ten years
| previous: Mark Buckingham I've used the c.t. style standby sw... -- 12/28/1999 7:57 PM |  |
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Re: placement of a standby switch
 12/29/1999 3:47 PM |
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Bruce | Re: placement of a standby switch The problem stems from the large value dropping resistor on the high voltage AC line to the rectfier diode in the bais supply. That resistor and the bias supply's filer cap form an RC circuit with a long time constant. Much longer then the time to charge a filter cap in the B+ rail. As an example, it might take three or four seconds to charge up the B+ rail but the same amp might take 20 or 30 seconds to charge up the bias supply rail. If the the amp is not cathode biased, then the B+ will be on the power tubes for a length of time with virtually no or very little bias voltage, as the bias -DC supply is charging it's filter cap through that large value resistor. The tube will be conducting too much DC idle current during this and cause unneeded wear and tear on the power tubes. Bruce |
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