[AMRadio] WTB SB-220


Gary Blau gblau at w3am.com
Sun Sep 26 21:22:39 EDT 2004


I've always found more RF power, at least in significant iterations of
~100watts, can make a big difference on the air in cutting thru noise
and band conditions.  But what's more important is full modulation.
    
One potential benefit of running a -modified- Viking or Ranger, etc.
into an amp like the SB220 is you can then concentrate on improving the
modulation performance of the exciter xmtr.  This can in turn deliver a
more effectively modulated signal thru the entire system and thereby on
the air.  
Add that to the increased power ability of running a fully modulated
~400 watts carrier, and a case can be made that this is one of the
easiest ways to get a big AM signal on the air.  
The easiest is to use a rice box for an exciter, but that's another fist
fight.

The Viking would have to be modified a good bit to optimize this
approach.  The first problem being reducing the RF output to the 10-25
watt level that the SB220 will want to see.  I've never had a VikingII,
so I can't say for sure, but my first thought is to try a variable PA
screen voltage scheme.  (I did this to good effect in my Ranger.)  You'd
probably have to remove one of the 6146's in the Viking, and make other
changes as well, but the idea is that not only will you be able to vary
the drive to the amp, but it will also give the huge benefit of much
higher positive peak modulation capability.  Positive peaks can easily
go way beyond 100% as the PA now is operating well below its peak
dissipation point.  Even if you're not a believer in hugely asymmetrical
'supermodulation', having an xmtr that can easily handle it will still
be a big improvement over the 'stock' Viking.  

Loudness is where it's at to get thru on a noisy band, but having an
extra 100-200watts as well makes a potent combo.

g


W4AWM at aol.com wrote:
> 
> << I am looking for a Heathkit SB-220 to run about 300 watts on AM using the
> Viking II to drive it. >>
> 
> Hi,
> 
> If you are getting the full output from the V II into a good well matched
> antenna, a couple of hundred more watts is not going to make any significant
> difference on the receive end and will only serve to heat up the shack and run up
> your power bill.
> 
> 73,
> 
> John,  W4AWM




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