Mike,
I'm just tuning into this thread now, so if this has been covered, sorry.
The inductance computation of a coil with a slug in the middle of it is
quite different from one that is air-wound. Did you account for that? Well
come to think of it, your method should factor that out, but only if the 40
coil's permeability is similar to the others.
The question you really want to ask from an SB200 owner is HOW MANY TURNS?
That would remove slug composition as a variable.
But perhaps your problem lies elsewhere. Have you looked closely at the
bandswitch? Can you verify that the exciter is "seeing" this coil when you
switch to 40? If you were able to arrive at close values using your
back-compute method on the other bands, I see no reason why it shouldn't
have worked on 40. You've determined the wire itself (when you removed it)
wasn't broken. I presume you've determined then as well that it was properly
soldered and thus connected. You didn't say, but I also presume that the
slug hasn't broken and half of it isn't sitting in the guy's shack.
If you can verify the coil form is intact, the wire was intact, and your
computations regarding the new cap are correct, I'd start looking elsewhere,
with the original winding and your computed cap value.
Start at the input wafer to the bandswitch, me thinks.
My 2-cents. Advice probably worth much less...
73 and GL,
Gary W2CS
> -----Original Message-----
> From: amps-admin@contesting.com [mailto:amps-admin@contesting.com]On
> Behalf Of Mike Baker
> Sent: Saturday, November 02, 2002 2:39 AM
> To: AMPS REFLECTOR
> Subject: [Amps] Heathkit SB-221 input network help, the saga
> continues....
>
>
> I'm back again with more info about this project.
> I decided to examine the input network for the SB-200 and compare the
> parts and their values to the ones in the SB-221. VERY interesting!
> All of the coils had the same part number EXCEPT the 40 meter
> coil. SO, to
> see if my idea was going to work, I took the values from the 15meter coil
> set in the 200 and added the only missing part (a 75pf cap) and
> away we go,
> it worked and tuned up great! HOT DAMN, I'M ON A ROLL!! Of to try
> 20meters. Checked the values and added a parallel cap to the caps already
> in place to duplicate the values of the SB200 and BANG, it tuned up like a
> champ with a minimal SWR!! YEAH! OK now on to the big one of 80 meters.
> Again added the necessary parallel caps and retuned and all was good with
> the world. Last but not least was the most critical band as it
> was the one
> the amp would most likely spend most of its time on, 40 meters.
> This is where Murphy decided to pay a visit. Put in the
> matching values
> and got 5:1 SWR that would not tune out. CRAP. Ok, so someone else said
> the input impedance is about 200 ohms. Off to the computer to
> use a program
> called Pi Net to evaluate the stuff I had been using...
> Using a Q of about 3 to 4 and matching 50 Ohms to 200 Ohms in and out on
> each of the other bands I had success with produced values that
> very closely
> matched what I had used for the caps. Using that result, I checked 40
> meters and got a value of coil that was just under 2 microhenrys. 1.92 to
> be exact. Using the wire table from the hand book and measuring the wire
> size on the 40 meter coil came up with something just a hair over
> .026 which
> appeared to be a 22 Ga. enameled wire. Counted the turns and came up with
> 17 and a half. Ok, so that info used to calculate the coil value
> gave me a
> result that was much too small for 40 meters with the cap values
> I had used
> from the SB200 design so I refigured the coil necessary based on 1.92Micro
> henrys with a 22 GA. wire and got something like 21 and a half turns. I
> took the old wire off and wound the new coil. Something didn't look quite
> right however as the new coil took up way too much space on the form
> compared to the original. In fact it appeared to fill the form almost as
> much as the 80 meter coil winding does!! OOPS! Don't think I got that
> quite right but lets try it out and see!!
> NOT! Way out in left field... Damn!
> OH, I almost forgot, before I removed the old winding but
> before I added
> the additional caps, I tried to use a old Millen dip meter to
> check out the
> resonate point of the input network... It appeared to have a big dip at
> around 11Mhz. and not 7Mhz. that I expected. Hummmmm. Add the new caps.
> Try dipping again. NOTHING changed! Yet I could still tune the coil with
> the slug and make it change the resonate point but the lowest
> point I could
> find was still 11Mhz.!!! HUH!! Unfortunately I lent my MFJ-249B analyzer
> out to a friend who hasn't returrned it to me yet so I couldn't just keep
> moving stuff around until it became resonate at 7Mhz. while testing at no
> power applied. Had to do it the old Hard way. Make a change,
> hook the amp
> back up again and try again to get the input SWR to get down to something
> reasonable. Repeat as necessary, again, and again, and again, etc.
> So now I have all but 40 meters working fairly well but am completely
> frustrated with trying to get it to match.
> DOES ANYONE HAVE THE ACTUAL WIRE SIZE AND NUMBER OF TURNS USED ON THE
> SB-200 40METER INPUT COIL!!!
> The coil used in the SB-200 for 40Meters is numbered
> "40-592". The coil
> used in the SB-201 is numbered "40-1980".
> The 80meter coils in both rigs are numbered 40-591.
> The 20meter coils in both rigs are numbered 40-593.
> The 15meter coils in both rigs are numbered 40-727.
> The 10meter coil in the SB-200 is numbered 40-728.
> If anyone has one or more of these 10 meter coils lying about
> and would
> like to see them have a good home, please contact me and quote me a price.
> I'll also take a 40-592 SB-200 40meter input coil if someone has
> a spare one
> as well. Then all of this would be moot as I would have it working by
> now!!!
> OH, BTW, to the fellow who told me about using a toroid wound
> 4:1 balun
> as a replacement, I pulled apart a 4:1 balun designed for wire
> antennas and
> took the ferrite rod balun out of it and tried to use it on the
> input. NOT!
> VERY BAD MATCH! I figured one broadband 4:1 matching transformer is about
> as good as another at this 100 watt power level but it still didn't work.
> So, back to my original request.
> Any ideas? I really want to get this thing finished and off my bench
> and back to its owner so I can pack up my buddies C-Line and get
> it back to
> him. (Don't have my TS-930 back from repair yet so I needed to keep the
> C-line as a testing exciter!) That's another story.
> OK guys. As Paul Harvey would say, "now you know the rest of the story".
> HELP!
>
> OH, BTW, thanks to all who have and are willing to lend a hand to this
> project. I do appreciate the effort.
>
> Mike Baker K7DD
> k7ddmjb@qwest.net
>
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