On Dec 7, 2005, at 3:04 AM, Will Matney wrote:
> Alek,
>
> I'm glad this fixed your amp, and was a blessing in disguise to prove
> a point that not all amps of one model are stable. In other words,
> even though an amp may be stable, another of the same model may
> exhibit signs of parasitics, and act squirelly like this one. There
> was a test done to prove that no such things as parasitics existed
> using 1-2 amps which were stable anyhow. The test did not use other
> amps of the same model which shown signs of parasitic action. This
> throws that test out the window, and proves the point. I'm sure Rich
> Measures, and a few others know of what I speak, and can concur. Even
> though other FL-2100B's may be stable, it does not necessarily mean
> all are (same with any amp of any model). It also proves that
> parasitic supressors do in fact work, do their job, and that nichrome
> supressors work where standard supressors using tinned wire may fail
> due to a lower impedance.
Gentlemen -- Using a Ni-Cr L-supp is not the only way to build a
parasite suppressor with lower VHF-Q - and thereby reduce VHF
amplification in an HF amplifier. . Ohmite® has a new line of low-L
film resistors that are capable of dissipating enough P to serve as
R-supp when silver (Ag) or copper (Cu) is used for L-supp, and do so
Without increasing VHF-Q. Thus, those who prefer to use silver
suppressors for cosmetic reasons can now do so without inviting
squirrels by increasing VHF-Q. The tradeoffs are: increased cost of R
and the need to provide a heat sink for the suppressor. In order to
convert an existing Ni-Cr suppressor to a beautiful silver-plated-strap
parasitic suppressor Without increasing VHF-Q, increase L-supp by c.
1.7x and change R-supp to one of the new Ohmite units that can
dissipate c. 3x as much P as the old R-supp.
> I would say your experience summed it up nicely! Thanks for letting
> all of us know th
> e outcome of your project.
>
> Best,
>
> Will
>
> Amateur Transformer
>
>
>
> *********** REPLY SEPARATOR ***********
>
> On 12/7/05 at 5:05 PM Alek Petkovic wrote:
>
>> Thanks to all who offered their assistance regarding the arcing 2100B.
>> The
>> amp has been stabilised.
>>
>> Dave, W8NF and Rich, AG6K were instrumental in curing the problem.
>>
>> I checked the 33 Ohm grid resistors and they were a bit higher than
>> spec.
>> They were not the original items. I changed them for some 30 Ohm
>> units and
>> added around 1000pF to the existing 200pF grid capacitors.
>>
>> As well, I made up some Nichrome suppressors from a spare kit I had
>> lying
>> around. With these and the grid mods, the amp has become
>> unconditionally
>> stable when keyed up with open circuit input and output terminals.
>>
>> Before, I added the nichrome suppressors, I installed a couple of good
>> suppressors from a previously modded 2100Z. With these installed,
>> with the
>> grid mods, the amp still produced a purple arc between the plates of
>> the
>> loading cap.
>>
>> I carried out tests for arcing after each step described above. It
>> wasn't
>> until all the mods were done that the amp started to behave.
>>
>> I hasten to point out that the amplifier seemed totally ok before any
>> mods
>> were done with a radio on the input and a load on the output. It was
>> only
>> by chance that I had the amp on the bench with nothing connected to
>> it.
>>
>> Other 2100B owners might care to experiment along the same lines with
>> their
>> amp.
>>
>> 73 All,
>> Alek. VK6APK
>>
>>
>>
>> http://www.qrz.com/vk6apk
>>
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>
>
>
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>
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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