Topband: de n7dd

[Ted Kirst]

"MaxGain Systems has a surplus Jennngs 500pF/20KV cap for about $350"

This is the one being used on my T and no problems at 1.5KW.

73, Ted: W1GL

>
> --- Original message ---
> Subject: Re: Topband: de n7dd
> From: Paul Christensen <w9ac at arrl.net>
> To: topband <topband at contesting.com>
> Date: Thursday, 09/01/2020 10:25 AM
>
>>
>> does anyone know of a HV (20KV) capacitor with a value of 
>> approximately
> 500 pf that has a NPO value?
>
> Once you get above about 100pF, NP0 options are very limited.  Be 
> mindful of
> the RF current magnitude in the application.  Small doorknobs can heat 
> and
> change in value.  In fact, I am dealing with this issue now on a 160m 
> T
> vertical.   My hope was that a paralleled pair of HEC doorknobs would 
> work
> in a NEMA 4x4x2 enclosure at the base.  The fit is fine, but the caps 
> are
> overheating in FT8/RTTY modes.  The fix will involve replacement with 
> a
> vacuum cap in a larger enclosure.
>
> MaxGain Systems has a surplus Jennngs 500pF/20KV cap for about $350.  
> Also
> consider transmitting mica capacitors.  Both will be quite large but 
> will
> meet your NP0 requirement.  Kintronic Labs sells a new 500pF/20KV mica 
> for
> about $650.  These are typically used in AM broadcast installations.  
> In
> time, you can likely find these at lower prices.  The most common used 
> mica
> will be manufactured by Sangamo.  If you're in a rush, be prepared to 
> pay
> more.
>
> Paul, W9AC
>
> _________________
> Searchable Archives: http://www.contesting.com/_topband - Topband 
> Reflector
>