The Broadcast Electronics FM transmitter power supplies for 1-3.5 kW tubes
and single phase power used a polypropylene capacitor and a choke designed
to be in parallel resonance at low current, to prevent the power supply
from soaring when excitation was removed from the PA. So in normal
condition with carrier, the resonant freq shifted above 120 Hz, as L was
reduced with DC current through it. Hundreds of transmitters were made
this way for over a decade. The peak voltage across the capacitor and
choke is quite substantial during the times that the resonance is
exactly at 120 Hz, so the cap needs to be rated to handle the heating
and corona.
John
K5PRO
> Message: 9
> Date: Sun, 3 Apr 2011 21:00:39 -0400
> From: "Gary Schafer"<garyschafer@comcast.net>
> Subject: Re: [Amps] Alpha vs. Henry
> To: "'Carl'"<km1h@jeremy.mv.com>, "'Fern'"<crc@cyberlink.bc.ca>,
> <amps@contesting.com>
> Message-ID:<A20FA92D3533419CB110E330076B47E8@garyPC>
> Content-Type: text/plain; charset="us-ascii"
>
> Not according to Collins. They say that the choke should be resonant at 120
> Hz with minimum critical current, eg bleeder current, which keeps voltage
> from soaring.
>
> As current draw increases the inductance of the choke will drop, going out
> of resonance and increasing ripple voltage out of the supply.
>
> 73
> Gary K4FMX
>
>> -----Original Message-----
>> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
>> On Behalf Of Carl
>> Sent: Sunday, April 03, 2011 7:14 PM
>> To: Fern; amps@contesting.com
>> Subject: Re: [Amps] Alpha vs. Henry
>>
>> The choke/capacitor combination should be resonant at 15-20% above 120
>> Hz.
>> When the choke lets loose I dont know what the failure mode is but Henry
>> amps do it often. Poor manufacturing tolerance on the choke inductance
>> may
>> be to blame, I cant measure them once they are fried.
>>
>> Carl
>> KM1H
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