[Amps] plate bypass capacitor

[Carl]

By using a low value plate choke it is fairly easy to eliminate any ham band 
resonances. As bands were added the problem got worse (especially 12M) but 
there are several good designs now.

The low inductance choke used on 160/80M still requires a low reactance 
bypass cap. Using a HV capable scope probe will confirm the RF coming thru 
many Dentrons for instance that use only a 500pf bypass. A .01uF takes care 
of the problem and keeps the electrolytics happy. Ever notice how prone 
Dentrons are to blowing filters and transformers? There is nothing wrong 
with the PS design. Several other amps are in dangerous territory using the 
more common 1000pf on 160M.

Carl
KM1H


----- Original Message ----- 
From: "Bill, W6WRT" <dezrat1242 at yahoo.com>
To: <amps at contesting.com>
Sent: Sunday, August 09, 2009 12:30 AM
Subject: Re: [Amps] plate bypass capacitor


> ORIGINAL MESSAGE:
>
> On Sat, 8 Aug 2009 22:59:20 -0500, "Gary Schafer" 
> <garyschafer at comcast.net>
> wrote:
>
>>
>>What happens on 160 meters and even 80 meters with a choke that is "too
>>small" for the frequency involved is that it is operated in a parallel
>>resonant mode with the plate tuning capacitor in order to provide a high
>>enough impedance.
>
> REPLY:
>
> A "too small" choke is indeed in parallel with the tune cap, but it had 
> better
> not be *resonant* with it or fireworks will follow. The relatively low 
> reactance
> of the "too small" choke is compensated by increasing the value of the 
> tune
> capacitor, but that is not resonance, just the normal way opposite 
> reactances in
> parallel combine in a non-resonant manner.
>
> Resonance is where XsubL = XsubC, and that is not the case here, far from 
> it.
>
> 73, Bill W6WRT
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