[Amps] question for you experts...

[Roger (K8RI)]

On 3/27/2012 10:20 PM, Gary Schafer wrote:
> 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.

It's more than just the antenna connector.  Add feed line and antenna.

The practice of the choke goes way back to when the legal limit was 
considerably less than today and it applies to transmitters as well.  
Back then receivers had either the same  chokes or neon lamps across the 
input terminals.

Voltages have gotten much lower in transmitters, transceivers, and solid 
state amps, but there is a new...well, they have been around for a long 
time, but there are now more of them and even commercial amps have a lot 
more muscle in the power supply.

I think the idea of the choke is a good one, but maybe we should 
consider a choke with notably more current carrying capability.  Will 
that little choke blow and clear, or will it offer enough delay to blow 
the fuse or trip the breaker?  Of course the average ham is likely to 
reset and try again.  If the choke cleared, every thing is likely to 
work just fine except for the few thousand volts that are now out there 
on the vertical antenna in the wife's flower garden, or the low hanging 
end of the droopy dipole.  OTOH antennas that are at DC ground should 
pop the fuse every time.

As far as static electricity, I've seen a ground mounted, quarter wave, 
40 meter vertical in a windy snow storm produce fatter and much longer 
sparks than any ignition system.

73

Roger (K8RI)


> 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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>> 03/27/12
>
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