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Re: [Amps] SB-200 circuit breakers

To: <>
Subject: Re: [Amps] SB-200 circuit breakers
From: "Tom Osborne" <>
Date: Sun, 26 Aug 2007 18:35:25 -0700
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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


> 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

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