[Heathkit] RE;SB-201 band switch (k1mcn-@verizon.net)

[Jim Brannigan]

> Hi,
>
> Thanks to all who have given me some good ideas on acquiring a replacement 
> switch for my SB-201 project. I am getting a band switch with tank coils 
> from Ron W2CQM. I am also looking at the new one on E-Bay I may if the 
> price doesn't go to high pick it up as a spare to have on hand.
>
> I do have a couple of questions though;
>
> 1)I want to stop the oscillations and I have built a set of new 
> suppressors for the amp from a kit that I got from Rich Measures. I have 
> used this same kit on a SB-221 that had serious oscillation problems.
> My question is are there any other things I should be looking for to stop 
> the oscillations
>
The Measures Kit solved all the problems in an SB-220

> 2) I want the amp to present a real 50 ohm match to the Icom transceiver I 
> am going to use it with. I looked on the web and found some input mods 
> that I can implement I don't have the equipment to test the input like was 
> used in the article so I was thinking I could use my MFJ antenna analyzer 
> with the transmit relay energized to look at the input impedance of the 
> input network so dial it into a real 1 to 1 match. will this work?
> Should I have the tubes in and on to do that and there is a filter network 
> on the SB-201 between the input network and the tubes should I remove that 
> or leave it in place? and what is it intended to do?

Got it almost right.  The analyzer is the right instrument, but you need to 
simulate the impedance of the 3-500's at the output of the network.
Remove the tubes and replace them with resistors of the correct resistance. 
The Handbook should have the correct input impedance for the 3-500.
There was a QST article from the early 70's that detailed this procedure.

Jim
>
> Thanks for all your help,
> Matt
> K1MCN