Hi Carl
Filter caps have been recently replaced. They are 100uf at 450 volts. I see
in the schematic that the originals were 125uf. I will do the 'heat' test
and see if they do in fact get warm.
Tubes were replaced just 3 or 4 months ago. They are Taylor tubes.
It is a problem that has just reared its ugly head in the past few weeks. I
used to run the amp around 300 watts on RTTY with no problems, but just
lately it has started tripping the one breaker, and only at 200 watts.
I guess I could just solder a wire across the breaker :-) 73
Tom W7WHY
> Three possibilities come to mind.
>
> - Defective breaker. Possible but quite rare.
>
> - Leaky filter caps. A very good possibility if they are original. Leave
> the amp on for a half hour or so and then shut off. Make sure t>he HV is
> down to zero and pull the plug. Feel the caps. If they are >more than
> just barely warm they should be replaced. The plate meter >will not show
> the capacitor or bleeder current. Get 220 MF 450V >Cornell Dublier 381LX
> series caps from Mouser. They are snap locks >but all can be oriented to
> fit existing holes. Replace the 8 bleeder resistors with 75K 3W MOX, also
> from Mouser.
> - Bad tube or tubes. Actually not bad but not compatible with the SB->200
> design. Some >Chinese and especially Russian tubes have different
> interelectrode capacitances and lower mu than the original Cetrons >and
> become unstable. Unless you want to install a neutralization circuit >and
> possibly increase the operating bias the best step is to replace the
> >tubes. There are still many good and even NOS Cetrons around. >BTW, what
> brand are they?
>
> Carl
> KM1H
>
>
>
>
>> Hi All
>>
>> On my SB-200, the front circuit breaker trips after half hour or so of
>> operation on RTTY. If running RTTY, I usually keep it down to 200-250
>> watts. It is the same breaker, the front one, that always trips. After
>> it
>> cools down a bit, it will come back on. The plate current is only running
>> about 300 ma or so.
>>
>> The tubes are fairly new (4 months) and don't run red when operating RTTY
>> at
>> 200-250 watts. I also have some muffin fans on top with the lid open to
>> take out some of the heat.
>>
>> In looking at the schematic, the breakers are in the primary of the power
>> transformer. What causes them to trip, heat? There doesn't seem to be
>> that
>> much with the extra fans on top. 73 and thanks
>> Tom W7WHY
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|