sb-201

Sat May 24 14:12:41 EDT 2008

On 23 May 2008 at 19:58, Terry England wrote:

> I made a few tests into a dummy load and this is what i found. Not sure about the readings because the meter acts funky to me.
> 80m 600w
> plate 400ma
> grid 40mil
> low swr

Do you mean the SWR between the amp and dummy-load, or between 
the driver and the amp?

> 40m 300w
> plate 400ma
> grid meter deflects backward's

Interesting....

> low swr
> 20m 350w
> plate 300ma
> 20mil
> swr was hi
> 15m 10m no output
> plate 80ma grid very little movement hi swr
> 10m plate 60ma grid very little movement
> hi swr
> I would say that this amp is in a mess but i will get it going again like it should. Tnx w9cau

Good man.

There is a lot of information out there on fixing those things. Carl KM1H 
is a recognized expert on those amps. He may be able to help. There is 
a Dutch site that I find especially interesting.

They really are, basically, an excellent amp, with a few things that can, 
now, be done a bit better.

The input circuitry is one area that needs "tweaking". The input SWR on 
my SB-200 is 1:1 in the center of every band but 10 meters now, and I'll 
get that one tweaked when 10 becomes "interesting".

The filament choke is a bit low in inductance for 80, but works 
adequately. I haven't changed mine yet, but plan to in the future.

The plate RF choke is also a bit low in inductance, but mine had already 
been changed for one with more inductance before I bought the amp. I 
think mine is 2.5 mH now. The original one was 1.1 mH. as I remember 
it.

The electrolytics in the power supply are sometimes a problem this 
many years after the amp was first built. Mine are original and still seem 
OK, but I will be changing them eventually. The new capacitors are so 
much smaller and lower in leakage that they take up much less space 
and run cooler.

I'm a firm believer in the adage, "If it ain't broke, don't fix it."

Ken Gordon W7EKB

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