[Heathkit] Heath SB 200

[John King]

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