[Heath] SB-200 findings.

[Kenneth G. Gordon]

Over the past month or so, I have been experimenting with my SB-200 some more.

1) Since I had a spare filament choke, I added that in series with the one that was already in 
the amp. I did this with the idea of learning what difference raising (doubling, in this case) the 
value of that choke would cause on the higher bands when I complete my mod to add 160 
meters.

What I found was that the input SWR did NOT change on any band 40 meters and higher, 
but it severely affected the input SWR on 80 meters, requiring that I change the 80 meter 
input network tuning capacitor from 470 pfd to 330 pfd to achieve a 1:1 SWR at 3750 Khz 
(center of the band).

This indicates to me that the filament choke was an active element of the input circuitry on 80 
meters (which IMHO should NOT be the case), which further indicated to me that the value of 
that filament choke was too small from the beginning, even for 80.

Efficiency seemed to be improved on 80 meters as input drive levels could be reduced for the 
same power output as before.

2) One thing that has always bothered me about my SB-200 was that the plate loading 
capacitor had to be "bottomed out" (i.e. fully meshed) for maximum output at the low end of 
80 meters, and I felt that it never was really properly adjusted to peak in that portion of the 
band. (In fact, this same thing was true about my first Heathkit transmitter, the DX-35).

Calculating the peak voltage at 2KW output into 50 ohms, I arrived at a peak voltage of about 
330. Therefore, just to check, I paralled C-27 (originally a 500 pfd 2KV capacitor, but mine 
had been replaced before I got the amp with a 600 pfd 15KV door-knob) with a 500 pfd 1KV 
mica cap.

This brought the loading cap up to about 3 on the front-panel markings and allowed me to be 
certain that the loading control was peaked appropriately.

Further experimentation and documentation will be done to determine if this effects anything 
else, for instance, if I can still peak the loading control at the HIGH end of 80 and/or 40.

Ken W7EKB