[Amps] TITAN II tuning and loading padder capacitors

[Fern]

Hi David:  I had a similar problems with my Viewstar PT-3000A amplifier (has 8877 in final) and the loading would drift on 160 meters as the value of the ceramic padder(in loading circuit) used on that band was changing value especially under key down condition. I replaced it with a mica type which is the only type to use for this application and at a much cheaper price. What value is your ceramic cap with the problem?
 73 from Fern  VE7GZ


----- Original Message ----- 
From: "David J Windisch" <davidjw at cinci.rr.com>
To: <amps at contesting.com>
Sent: Sunday, December 06, 2009 12:30 PM
Subject: [Amps] TITAN II tuning and loading padder capacitors


> I'm testing an amp, and it puts out 1.5kW+ 160-10M, but the power drifts, on 160 and 80.  
> 
> Searched the archives for fixes, and (from 9 years ago) found posts indicating that the padders in the loading portion of the tank circuit heat up from r-f current, and change value.
> 
> Checking RF Parts for doorknob-style capacitors, I see only N750 temp coeffs in suitably-valued (150 pF to 1500pF) components.
> 
> The plate tuning capacitor also has this same style padder switched in on 160M.
> 
> Are these N750 capacitors suitable as padders in this r-f application?
> 
> What's to do?
> 
> Thanks in advance.
> 
> Brgds,
> Dave Windisch, W8FGX
> 
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