[Amps] [AMPS] Re: FL-2100B Failure

R.Measures r at somis.org
Wed Feb 23 10:48:20 EST 2005


On Feb 22, 2005, at 3:10 PM, Joe Subich, K4IK wrote:

>
> Kevin writes:
>
>> with respect to the burning on the plate choke: yup it's only
>> in certain areas.  So the comments about vhf parasitics are
>> probably right on, if that's a key indicator.
>>
>> The 22 ohm suppressor R's physically looked okay, but I'll
>> be sure to measure them.
>
> These two observations point not to parasitics but an attempt
> to operate the amplifier on a band for which it was not designed
> perhaps 17, 12 or 11 meters.  Burning in certain areas of the
> plate choke indicates high voltage at that point, probably due
> to a resonance.  That often happens to older amplifiers not
> designed with "WARC" band operation in mind.

   Joe:   When, during WARC-band operation in a non-WARC band amplifier, 
one burn mark appears at the top of the HV-RFC, it's probably due to a 
WARC-band resonance, however, when multiple burn marks appear, the 
problem is likely VHF resonances absorbing VHF energy.  This problem is 
easy to confirm with a dipmeter:  Measure the choke resonances from 50 
- 150MHz.  Measure the anode resonances from 50 - 150MHz at the DC 
blocker capacitor.  If two coincide, odds are that it toasted the 
choke.
>
> Some very good examples are the MLA-2500 which had a resonance
> near the 17 meter band and the Alpha 76 series of amplifiers
> that intentionally had a choke resonance around 25 MHz which,
> while it prevented operation on 11 meters, happens to prevent
> the amplifier from being used on 12 meters.
>
> 73,
>
>    ... Joe, K4IK
>
>
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>

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org



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