[Heathkit] Heath SB 200

[Steve Sutfin]

> John,
>  There seems to be a similar common problem with the FL-2100's  
> (SB200 clone). There was a discussion on the amps & qsl reflectors  
> about low bias current and pointed to the grid to ground caps (I  
> believe C14 & C15 in your case):
> http://lists.contesting.com/archives//html/Amps/2003-11/msg00082.html
>  Some have suggested 1000pf-2mf as a replacement:
> http://web.archiveorange.com/archive/v/0RLC1ZrJ4ex0tyT80hMQ
>  I have the same low bias current with my 2100 and just received my  
> 1000pf/500w dipped mica's from Mouser but haven't had time to  
> install yet. I'm not 100% sure this is the cure but have my  
> soldering irons crossed.
> gl,
> Steve k7dna
>
> On Jan 15, 2012, at 12:50 PM, John King wrote:
>
>> 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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