>
>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. . 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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