Since time began small chokes were placed across the amp output pi-net. I
don't know where the term got started but everyone seemed to call them
"safety chokes" in case of plate blocking failure but as Vic says a 125 Ma
choke isn't going to last long.
The real reason they are there is to keep the plate tune and load caps from
charging up to a high voltage and arcing from leakage thru the plate block
capacitor and or static charge from the antenna. The "safety" factor would
come into play if someone were to touch the antenna or antenna connection
when the capacitors were charged.
73
Gary K4FMX
> -----Original Message-----
> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Bill Turner
> Sent: Tuesday, February 13, 2018 11:50 AM
> To: Amps group
> Subject: Re: [Amps] Series C in amp output
>
> ------------ ORIGINAL MESSAGE ------------(may be snipped)
>
> On Tue, 13 Feb 2018 07:41:49 +0200, Vic wrote:
>
> >
> >I have always thought those 'safety' chokes aren't worth much. The 2.5
> mh chokes often used in that spot are rated at 300 or even 125 ma, and I
> suspect they would open long before the plate supply fuses would blow.
> >But note that the capacitors Martin mentioned are only rated at 500v,
> so they aren't much of a safety feature either!
> >
> >Vic 4X6GP
>
> REPLY:
>
> That's a good point. Perhaps the best measure would be a custom choke
> wound with heavy wire (18 gage or heavier) wound on a ferrite core. It
> would have to be carefully checked for resonances in the ham bands.
>
> If your antenna has DC continuity, that itself is protection, but
> antennas such as simple dipoles do not.
>
> Whichever approach you prefer, please do something. You REALLY don't
> want HV on the antenna!
>
> 73, Bill W6WRT
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