[AMPS] Purpose of CW/SSB switch

[Rich Measures]

>
>What is the true purpose of the CW/SSB switch on many of the older linear 
>amps ?
>
The duty cycle for SSB is about 15%.  The duty cycle for CW is about 
double that.  To obtain 1500w keydown output with 60% efficiency, a 2500w 
HV supply would be needed.  The avg. ham amplifier has a c.600w HV 
supply.  This is ok for 2500w pep input on SSB, however, it isn't as ok 
for CW.  Reducing the anode voltage and current for CW is a satisfactory 
workaround.  On the receiving end, who could notice c. 1/4 of one S unit?

>Was it simply to ensure that you stayed within the old power INPUT 
>regulations when in CW mode, or is there some other good technical reason ?
>
> Obviously the reason I'm asking is that I can't see a good technical 
>reason for the switch.  Actually I see good reasons for not having it but 
>I need someone to verify my understanding.  (I wasn't planning on having 
>one on the 4-1000 amp I'm building).
>
If you have a large enough power supply, you don't need CW/SSB switch, 
Phil.  On the other hand, 7kV is ideal for SSB with an 8166/4-1000a, but 
it is a bit much for casual CW use.  .  Why not go with an 8171?  It 
drives easier, is easier to cool, takes up the same chassis space as an 
8166, requires no filament choke, uses a simpler tuned input, and can 
deliver seven more db if need be.  .This can come in pretty handy to 
compensate for additional path loss on 80m and 160m.    
-  later, Phil

Rich. Measures.  Web site:  www.vcnet.com/measures


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