On Sat, 28 Nov 1998 01:55:04 -0800 Rich Measures <measures@vc.net>
writes:
>
>>
>>Hi Folks:
>>
>>I finally got around to wiring the shack in our new home for 220VAC,
>and
>>plugged in my vintage SB220 for 48 hours of CW contesting. After the
>>step-start circuit disengaged, there was a load pop and flash from
>the
>>high voltage section behind the meters. The amp had been off for six
>>months. I checked the
>>AC mains, and found 245V! The old QTH had 220-225V ... and the amp
>had
>>run flawlessly at this voltage for 15 years. My theory (and I am
>asking
>>your opinion) is that the old filter caps probably decided the 10%+
>extra
>>voltage was too much! BTW, the diode board was replaced last year
>with
>>one of Harbach's.
>
>Why speculate? In less than five minutes, you could be looking at the
>
>electrolytics' vent holes. If you see white deposits, the caps are
>history. While you have it open, to reduce filter cap. temperature,
>the
>eight 30k 7w resistors should be beplaced with Matsushita 3w 100k ohm
>mof
>resistors, or something of equal quality.
BAD advice IMO. The caps should be checked with the original resistors
first for voltage drop. A good string will show a 10-20V variation at the
most. Replacing resistors across well aged caps could be asking for a
wide voltage variation and more failures.
73 Carl KM1H
. If the caps are ok, I
>would check the 0.82 ohm grid current shunt R. If the resistor is
>damaged, either a tube is gassy or an intermittent vhf parasite took
>place. . If the resistance of either one of the vhf supp. resistors
>is
>more than 50% too high, a parasitic is indicated.
>>
>- later, Dennis
>
>
>Rich...
>
>R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
>
>
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>
>
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