[Amps] question for you experts...

[Bob K6UJ]

Carl,

My Alpha 76CA is still running perfectly after the conversion to 3CPX800's and
the other items I did that you recommended here on the reflector.  I haven't tried 
putting a brick on the key yet though, hihi.

In a phone conversation with Commander amps before Palstar, hihi, I remember 
being told that  the choke is for safety in case the plate blocking cap shorts as you said.  
It may provide  damping to help prevent plate tuning cap arc overs also, but my understanding is
that the primary function is as you stated.

Bob
K6UJ  





On Mar 27, 2012, at 6:57 PM, Carl wrote:

> 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
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>> 
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