[Amps] Alpha vs. Henry

John Lyles jtml at losalamos.com
Sun Apr 3 19:10:19 PDT 2011


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 at comcast.net>
> Subject: Re: [Amps] Alpha vs. Henry
> To: "'Carl'"<km1h at jeremy.mv.com>, "'Fern'"<crc at cyberlink.bc.ca>,
> 	<amps at contesting.com>
> Message-ID:<A20FA92D3533419CB110E330076B47E8 at 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 at contesting.com [mailto:amps-bounces at contesting.com]
>> On Behalf Of Carl
>> Sent: Sunday, April 03, 2011 7:14 PM
>> To: Fern; amps at 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




More information about the Amps mailing list