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 Too high voltage out of the rectifier

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pixellany



Posts : 58
Join date : 2010-10-12

PostSubject: Re: Too high voltage out of the rectifier   Wed Oct 20, 2010 7:35 pm

You are in the ballpark with that voltage....If you have a high-impedance voltmeter (eg a VTVM) you can measure the bias right at the tube also.

Now--how about the missing resistor?

More on the thought process behind the trouble-shooting: The voltage on the bias string tells you the TOTAL B+ current for all tubes. By then looking at bias voltages and other evidence, we can compare to the specs on the tubes. Your schematic of course gives you a leg up by providing the expected voltages at various points.

I think someone already suggested that the voltages may actually be OK
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PTurney



Posts : 1
Join date : 2010-10-21

PostSubject: Re: Too high voltage out of the rectifier   Thu Oct 21, 2010 6:53 am

Hi,

I assume the value of the replacement C21 is correct at 30mfd? If this is too big the B+ will be increased. Check also that the replacement C21 is not bridged across the original, as this too could result in elevated C21 value.

As the input filter capacitance is increased the current thru the rectifier becomes increasingly impulsive and the output voltage increases. At some point the peak current of the rectifier tube will be exceeded, stressing the tube and leading to shortened life.

Paul www.tuberadioland.com
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