[Heathkit] Heath SB 200

[Carl]

The bias is determined by R-18, change value to what works.

But first be sure both tubes are conducting and that one of the grid 
resistors isnt open or a very high value.

Carl
KM1H


----- Original Message ----- 
From: "John King" <k5pgw at yahoo.com>
To: <heathkit at mailman.qth.net>
Sent: Sunday, January 15, 2012 3:50 PM
Subject: [Heathkit] Heath SB 200


>I am having the same trouble with my SB 200 that many others have evidently 
>had based on the many descriptions of the problems others have had.
>
> I have the same problem with two new RF Parts 572B tubes that I have with 
> the original Cetron tubes.
>
> Plate voltage is 2330  vdc with a Fluke multimeter with Fluke HV probe
>
> Bias voltage at tube pin is -134 vdc before keying up
>
> Bias voltage when keyed up is -2.1 vdc.
>
> The problem is that the idling plate current with no drive is 40 ma., 
> instead of the 90 ma. the two tubes are supposed to draw when keyed up 
> with no drive.
>
> When googled, there are numerous postings on the internet of this 
> identical
> problem. The problem is that I can't find any diagnosis or fixes for the 
> low idling current problem.
>
> How many of you have had this problem and what was the cause and the fix?
>
> Your experience and knowledge will be appreciated in diagnosing and fixing 
> this problem. Thanks and 73, John, K5PGW
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