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@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Greg Weinfurtner
Sent: 27 July 2010 03:37
To: amps@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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