[AMRadio] Swinging chokes

[Jim Candela]

Hi Guys,

    Just wanted to drop in and say that this discussion has been most
enlightening, and to add a twist to this topic.

    I have a Gonset Linear, the GSB-210 which has a choke input filter power
supply, and this was designed for all modes of operation including AM, and
SSB. I recently replaced the filter capacitors which were 5 times  100 uf @
450 volts in series, or 20 uf. I don't know about what choke is, but it is
"big". I replaced the old caps with 5 times 220 uf @ 450 volts (44 uf). This
was mostly a matter of what can I buy to fit into the old space. Modern caps
are much smaller then 30 years ago given similar ratings. Seems like by
'dumb luck' I did the right thing. I got my caps from Digi-Key in a few
days.

    The Gonset uses the choke on the negative lead. I wonder about this.
Some say the peak voltage the choke has to withstand is reduced this way.
The Gonset uses a FW bridge, and a 3K 80 watt resistor in series with the
Choke (power up & tune position) that gets shorted out in the operate mode.

    I never used negative lead filtering on my AM rigs because I normally
grounded the transformer CT, and use two 3B28's in a FW-CT rectifier
arrangement. I am afraid that a transformer designed to have the CT grounded
might arc out with negative lead filtering. Would a spark gap from the CT to
ground be advisable, or an R-C snubber across the choke to absorb the back
EMF kick when the choke field collapses?

Regards,
Jim candela
WD5JKO