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Re: [Amps] FL-2100B Fixed

Subject: Re: [Amps] FL-2100B Fixed
From: R.Measures <>
Date: Wed, 7 Dec 2005 04:49:32 -0800
List-post: <>
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
>> _______________________________________________
>> Amps mailing list
> _______________________________________________
> Amps mailing list

Richard L. Measures, AG6K, 805.386.3734.

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