[Heathkit] Heath SB 200

[Carl]

Those capacitors have nothing to to with bias voltage or plate current.
I use .01/1000V disc ceramic in parallel with the existing 200pf (if they 
are good) and that properly grounds the grids for RF by a factor of 10 over 
1000pf..

The FL-2100 has that plus a serious bias problem with import tubes and 
stability in general.

Carl
KM1H


Carl
KM1H

----- Original Message ----- 
From: "Steve Sutfin" <stephoto at mind.net>
To: <heathkit at mailman.qth.net>
Sent: Monday, January 16, 2012 11:59 AM
Subject: [Heathkit] Heath SB 200


>
>> 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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>>
>
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