[Heathkit] DX-100B Capacitor Question

[Garey Barrell]

Bruce -

OK.  I assume it is to limit the drive to the PA on the lower bands.  I don't see any reason why it 
would have to be rated at 2kV though.  1 kV should be plenty, and a lot easier to find.   I don't 
have a "B" schematic, so can't say for sure, but a lot of the DX series transmitters drove the 
6146's too hard on the low bands.  It would be interesting to see if the "B" version developed MORE 
drive in the 5763 to boost the high end and then the 68 pF cap to keep it down for the low bands.

Let us know what you find.

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>


Bruce Spacer wrote:
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> Thanks Garey and Lee for the quick reply.
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> This capacitor is between the plate of the driver (5763) and the driver section of the band switch.  It is not the big .001 uF in the final compartment, but the cap that goes from Pin 1 of the 5763 up through the deck and connects to the (driver) air variable.
>
> On my "B" schematic it is shown as a 68 pF which matches what I found in the radio (just measured at 70 pF).  On a DX100 (non B) schematic I have, the same capacitor is shown as a 0.001 uF.
>
> Big difference (>  10x) in values.  Perhaps another "B" owner can look at their unit and see what is installed.
>
> 73s,
>
> Bruce
> WB8VCM
>
> -------------------------------------------------------
>
>> Date: Wed, 11 Apr 2012 21:31:10 -0400
>> From: k4oah at mindspring.com
>> To: wb8vcm at hotmail.com
>> Subject: Re: [Heathkit] DX-100B Capacitor Question
>>
>> Bruce -
>>
>> Yes, that is a 2000V part.   All the diagrams I have here show a 1000 pF (0.001uF) at 2 kV.  I'm
>> assuming you meant the cap between the PA and Pi-Net.  The coupling cap between the Driver and Final
>> is also 1000 pF, but a 1kV part is sufficient here.  I can't think of any reason for there to be a
>> 68 pF in there, 500 - 1000 is much more typical in that location.
>>
>> 73, Garey - K4OAH
>> Glen Allen, VA
>>
>> Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
>> and TR-4/C Service Supplement CDs
>> <www.k4oah.com>
>>
>>
>> Bruce Spacer wrote:
>>>
>>> I am rebuilding a DX-100B and saw a posting that it would be a good idea to replace the 68 pF mica between the driver and final.
>>>
>>> The existing capacitor is a molded mica Sangamo.  It has no color codes, but on one side is stamped "68 5%".
>>>
>>> On the other side, it is stamped "2000 VW" (not WV).  It is arranged like a 6 dot format, and when you hold it with the arrow pointing right, the digit "2" is molded into the upper middle dot.
>>>
>>> Is this a 2000V part ?  A quick check of the Mouser site shows the typically available CDE micas (CDV19) are only rated up to 1000V.  Any suggestions for a replacement ?
>>>
>>> Thanks,
>>>
>>> Bruce
>>> WB8VCM
>>>
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