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@comcast.net>
To: "'Kathy Bookmiller'" <wb2aio@yahoo.com>; <Amps@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@contesting.com [mailto:amps-bounces@contesting.com]
>> On Behalf Of Kathy Bookmiller
>> Sent: Tuesday, March 27, 2012 5:11 PM
>> To: Amps@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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>
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