[Amps] More parasitic choke questions

[Carl]

With such a low Q involved the effect is miniscule and not noticed, it is 
mostly cancelled out by its own R. Of course the main L should be very low 
loss and the complete suppressor should not absorb any of the desired HF 
power.

 Ameritron has gone to the MOX resistor and mica caps. This was part of a 
long running argument between myself and a former forum member, in the 90's, 
who kept insulting my suggestion....based upon testing with 5W....and it was 
later found implemented in his companys amps (-;  No surprise standard 
performance there.

Carl
KM1H


------ Original Message ----- 
From: "Martin Sole" <hs0zed at csloxinfo.com>
To: <amps at contesting.com>
Sent: Tuesday, July 27, 2010 12:04 AM
Subject: Re: [Amps] More parasitic choke questions


> Oh dear, I really didn't want to drag this old horse from its resting 
> place
> to start another flogging match. Apologies to Greg though as my original
> message was rather cryptic in its reference to this particular idea. I'll
> stick with the design as it is though since this has worked fine for many
> years. The aging resistors are going high though so increasing the Q which
> may not be ideal. Looking at 3 amps, a 30L-1, a Henry 2K Classic X and an
> Alpha 78 all of them show an increase of R above the spec of the old 
> carbon
> resistors original value. In the case of the Henry the increase is about
> 100%!
>
> Interesting thought about adding XC to cancel XL in the resistor though it
> raises a couple of questions for me.
>
> If the problem of modern resistors is the small amount of L present then
> this is in parallel with the added L so reducing its total L. Increasing 
> the
> original L to offset this would seem appropriate. Would this not just have
> the effect of producing a double humped response? One being the self res 
> of
> L and the other being the series res of R and RL. I can appreciate that a 
> WW
> R would be less than an ideal PC but not sure why MOF or CF would 
> similarly
> be inappropriate.
>
> Martin, HS0ZED
>
>
>
>
> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
> Behalf Of Greg Weinfurtner
> Sent: 27 July 2010 03:37
> To: amps at contesting.com
> Subject: Re: [Amps] More parasitic choke questions
>
> Hi all,
>          I have a Heathkit HL2200 that was built by NC8V (SK). (Uses a 
> pair
> 3-500Z's) I bought it from him while he was still alive and he gave me a
> photocopy of modifications to help the stability.  One concerned the
> parasitic chokes.  It involved removing the current ones and just removing
> the wire off the resistor.  Then with the same amount of turns, it called
> for a piece of nichrome wire, (available out of a hair dryer, toaster, 
> oven
> element, etc.) instead of the copper wire.  So I used a silver brazing rod
> ($5.00 now...ouch...) to 'tin' each end so that it would be solderable.
> Then it called for me to wind the same number of turns over the resistor.
>
> Theory:  The nichrome wire exhibits resistance and instead of a direct 
> short
> like the copper wire did.  This resistance broadens the 'Q' of the choke 
> and
> helps quell parasitics.  It certainly helped in my amplifier, as I could
> tell an immediate difference, especially using a tuner with the ol'
> gal.
>
> A little off topic about the resistors but something to consider when 
> making
> parasitic chokes.
>
>
> Greg Weinfurtner AEE BSS
> NS8O
> 40192 State Route 689
> Meigs County
> Albany, Ohio 45710
> United States of America
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