As a vague rule-of-thumb, the value of the plate blocking cap should be 4 to
5 times the value of the tune cap at resonance for the frequency in use.
That would indicate 100 to 150 pf for 6M.
I use a 200 pf vacuum cap in my HB 8877 rig.
73, Barrie, W7ALW
----- Original Message -----
From: "David Craig" <davidhcraig@verizon.net>
To: "RICHARD SOLOMON" <w1ksz@q.com>; "Amplifier Reflector"
<amps@contesting.com>
Sent: Wednesday, May 27, 2009 9:56 PM
Subject: Re: [Amps] Doorknob Caps Needed: Background
> Dick, many use the stock 1000pf cap. I do too, but it makes me quezy
> as
> the RF current rating is being taxed or probably exceeded. That said, if
> you need a new one a 200pf 15kv would be ideal if you can find one cheap
> enough. Otherwise a Sprague et al rated at 15-20kV should be fine- lots
> of
> NOS 680pf et al out there for $3-5 at hamfests. I have one homebrew 6m
> amp
> using a single 7.5kv 200pf cap (same size as the 15kv so I have to
> wonder...). In my last homebrew 6m amp I used a pair of 100pf 15kV in
> parallel.
>
> 73 Dave
>
> ----- Original Message -----
> From: "RICHARD SOLOMON" <w1ksz@q.com>
> To: "Amplifier Reflector" <amps@contesting.com>
> Sent: Thursday, May 28, 2009 12:31 AM
> Subject: [Amps] Doorknob Caps Needed: Background
>
>
>>
>> Let me back up a tad on this. I am converting an SB-220 to 6 Meters.
>>
>>
>>
>> One of the questions I have is about the Plate Coupling Cap value. I see
>>
>> values of anywhere from 100 pF to 1,000 pF used. There must be some
>>
>> way to determine the appropriate value besides closing your eyes an
>>
>> picking one out of the box.
>>
>>
>>
>> I didn't find any specifics in the West Coast HB so unless I experiment
>>
>> with a bunch I am going to have to rely on what others have done.
>>
>>
>>
>> Maybe the answer is to use the one in the SB-220 ??
>>
>>
>>
>> Any thoughts,
>>
>>
>>
>> 73, Dick, W1KSZ
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>>
>
>
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