[Heathkit] SB 1000

[Mark S Graalman]

  Charles,

 As the idle current increases, is the bias voltage staying
the same? I'm not real familiar with the SB1000, but 
assuming the plate voltage at idle is 3KV with 80 ma
of idle current the plate dissipation is 240 watts and at
100 ma its 300 watts, a 3-500Z *may* very well
show SOME color at 300 watts dissipation.


Mark  WB8JKR


On Mon, 23 Feb 2004 10:11:42 -0600 Charles W BWW Burkhardt
<cburk001@juno.com> writes:
> Gentlemen; I hate to keep taking up space in this forum, but I am 
> still
> having trouble with my SB- 1000.
>    Many have responded to my questions and I have made the following
> changes:
>     Replaced the Zener with a string of 3 A diodes, replaced
> D401(although the original test OK). I am able to measure(very 
> carefully)
> the tube bias. 23 volts at idle, 7.3 volts on transmit. I used two 
> 1.2
> ohm resistors in parallel for the grid current meter.
>    With zero drive the tube draws 80 ma, which is correct.
> If I leave it in transmit with no drive the current slowly increases 
> to
> about 100 ma and the plates start to glow red.
> I'm afraid to continue to operate it with no drive since, if the 
> fuses
> don't blow quickly enough, it may take out the grid metering and 
> bias
> components.
>    Perhaps I am missing something critical. Any ideas, please. 
> Thanks.
> Charlie K0GPF
>    
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