On Fri, 27 Nov 1998 20:53:12 -0800 k7fl@juno.com (Dennis Ashworth)
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.
>
>Thoughts??
>
>Dennis, K7FL
>Battle Ground, WA
It could also be one of the tubes arced over and took out the bias diodes
and metering resistor. Hope you didnt blow the meter.
Good caps will handle a 245V mains with no problem but they may have
already been on the way out.
New Computer Grade CGS series caps are available at Mouser for decent
money. Replace a complete leg of 4 at the very least and measure the
voltage across the remaining 4....the drops should all be within 10-20V
of each other if the caps are good.
Check the grid chokes for an open and the 6 grid caps for cracked cases.
Install a 15 to 20 Ohm 20w real wirewound in the HV lead in place of that
little VHF choke as an arc suppressor.
73 Carl KM1H
___________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com/getjuno.html
or call Juno at (800) 654-JUNO [654-5866]
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|