[Amps] question for you experts...

[Gary Schafer]

Well Carl, which is it? You seem to be waffling both ways.

The only "safety benefit" that the choke offers is it keeps the DC voltage
at zero on the output terminal of the amplifier so you won't get zapped if
you should touch the antenna connector or an antenna connected that does not
have DC continuity in normal operation.

73
Gary  K4FMX

> -----Original Message-----
> From: Carl [mailto:km1h at jeremy.mv.com]
> Sent: Tuesday, March 27, 2012 9:58 PM
> To: garyschafer at comcast.net; 'Kathy Bookmiller'; Amps at contesting.com
> Subject: Re: [Amps] question for you experts...
> 
> The REAL reason was as I stated since it conformed with Handbook and
> magazine suggestions for decades prior.
> 
> The other reason was a secondary benefit found by accident and reported
> in
> Hints and Kinks if I remember.
> 
> Note I also said "theoretical" since the safety benefit is questionable.
> 
> Maybe Gary can impress us with a test to see which blows open first.
> 
> Carl
> KM1H.
> 
> 
> ----- Original Message -----
> From: "Gary Schafer" <garyschafer at comcast.net>
> To: "'Kathy Bookmiller'" <wb2aio at yahoo.com>; <Amps at contesting.com>
> Sent: Tuesday, March 27, 2012 9:27 PM
> Subject: Re: [Amps] question for you experts...
> 
> 
> >A lot of people think that the choke is there as a safety device in
> case
> >the
> > plate blocking capacitor shorts. Most chokes across the output are too
> > small
> > in current carrying capacity to be an effective safety device should
> the
> > plate blocking capacitor short.
> >
> > The real reason for the choke is to keep the output tune capacitor
> from
> > charging to some DC level and causing the tune capacitor to arc
> > constantly.
> > Most load capacitors are close spaced and only rated for a few hundred
> > volts. Even if a vacuum capacitor is used as a load capacitor the
> voltage
> > rating is often less than the plate voltage supply.
> >
> > If there is no DC path to ground on the output of the amplifier then
> that
> > puts the plate blocking capacitor in series with the load capacitor
> and
> > the
> > DC plate supply can charge the tune capacitor if there is any slight
> > leakage
> > in the plate blocking capacitor.
> > Another way the load capacitor can charge is from static if an antenna
> > with
> > no DC ground across it is connected to the amplifier. This will cause
> the
> > load capacitor to continually charge and arc.
> >
> > If you hear a constant timed "pop" in your receiver at regular
> intervals,
> > maybe a few seconds to several minutes apart, you may have an open
> choke
> > on
> > the output of the amplifier.
> >
> > 73
> > Gary  K4FMX
> >
> >> -----Original Message-----
> >> From: amps-bounces at contesting.com [mailto:amps-
> bounces at contesting.com]
> >> On Behalf Of Kathy Bookmiller
> >> Sent: Tuesday, March 27, 2012 5:11 PM
> >> To: Amps at contesting.com
> >> Subject: [Amps] question for you experts...
> >>
> >> I was doing some checking out everything on my amp. (NCL2000) and
> >> noticed that the 2.5mh choke that is after the loading capacitor in
> the
> >> amp. was open-connection/wire is gone. Looking at others amps., I see
> >> they all have them-it would be rfc3 in a SB200, 1.1mh., for example.
> >> Since they are in all amps, at least tube ones, what is it for? My
> guess
> >> it is to short out the HV if the coupling cap. shorted coming from
> the
> >> plates, but if I'm right, it doesn't seem heavy enough for a good
> power
> >> supply not to just burn it up and keep on putting the HV on the
> >> antenna/output.
> >> I think I can save the one in my amp. if I can get the paint off the
> >> wire by scrapping or chemicals and reconnect it, but by doing this,
> I'll
> >> eliminate one of the 4 sections on the choke, but doubt that change
> in
> >> value would be a big problem?
> >> Enlighten this poor QRPer,
> >> Kathy W2NK
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