Dear Bruce, et. al.,
I looked up my SB-200 notes and found the following. The input circuits are
L-networks on 80, 15 & 10, The input circuits are Pi-networks on 20 & 40.
For all the input circuits I found:
on 80, my SB200 input was good at 4000 KHz, not below. I moved the slug
in a bit and maybe added 40 pfd in parallel with the stock capacitor to get
a good average from 3.5 to 3.8 MHz.
on 40, mine was OK. I am sure I tweeked the slug to best SWR around
on 20 mine was OK as built. I had a friend with a bad input SWR and
found one of the two capacitors was defective. Replacing it brought it in
the middle of the band with low SWR throughout.
on 15 meters, I found the value of the inductor to be low and the
capacitor to be high. I changed the capacitor to either 47 or 51 pfd (maybe
it was 68 pfd originally?). On one unit I changed the 15 meter coil for a
20 meter coil and found good resonance. On a second unit I wound three
turns of coil on a pencil as a form and put it in series with the end of the
coil going to the band switch without the capacitor to ground. Then I had
enough inductance to minimize the SWR in the middle of 15 meters.
on 10 meters, I also found the value of the inductor to be low and the
capacitor to be high, again this is an L-network. I changed the capacitor
to either 42 or 44 pfd and increased the inductance, once by using a 15
meter input coil, and the other time by using 3 turns airwould of #16 or #18
hook up wire in series with the stock coil. For both 10 & 15, the coil
diameter ID is 5/16" by 1/4" long. That is 8 mm ID x 6+ mm long in metric
To loosen the slug in the coil, I had to warm an Allen Key with a
soldering iron or torch just a little bit to warm the slug so the wax would
I noted some early 15 meter inputs had a Pi-network, maybe pre-1972 when
I bought an SB-200 kit. I have no experience with them, except the values
should be proportionally lower than on 20 meters, like +/- 66%.
I no longer have any Heathkit amps, only a couple of cooling fans with
73, Good luck, George K8GG
----- Original Message -----
From: "Ballew, Bruce N" <firstname.lastname@example.org>
Sent: Wednesday, March 26, 2003 9:16 AM
Subject: [Amps] SB200 tuned input
> As a new amp owner, but with and old amp (SB200). I have other question.
> the way thanks to the all that answered my 1st question. We have it
> and are up to testing and hopefully operation.) On the tuned inputs on the
> SB200 I have ran the analyzer on the input and find that the only
> filter that appears to be tuned any were near the band is 40 meters. I
> check the SWR on this also and the any band, again that has a low SWR is
> meters. All the other coils/tuned filters are outside the band area. Is
> this normal for the SB200. If so has anyone tested the inputs to see what
> freq. that they are tuned to. And / or is there a way to tune them. I
> like to make sure that they are tuned where they need to be and insure
> proper operation of the amp..
> Thanks for any help.
> Amps mailing list