High Power HF BA's - How Many Categories

Mark Shaum k9tr at DTNSPEED.NET
Sat Mar 29 18:18:19 EDT 2008

> When I build the Amateur Radio High-Power Rig Web
> site how many categories would provide a valuable
> resource to the community?
> (Also, is the gathered preference that the site
> list power levels as DC Input with estimated final
> stage efficiency, DC Output, or PEP Output, or
> some combination of the three?)


Most of the rigs you've mentioned to date were orignally rated by the mfr 
for INPUT power ( peak envelope power for SSB or carrier for CW).  This is 
from the days when the FCC maximum allowed power was based on input power, 
not output.

Output is going to vary all over the place depending on band and mode for a 
given input power.  That's why the output power was generally left out of 
advetisements.  As a rule of thumb, the rigs will deliver somewhere between 
50 and 65% of their rated input as output power in class AB1 depending on 
frequency.  Input and output on CW is generally less due to limits on the 
power supply's ability to provide sustained B+ with a full carrier as well 
as tube overload/overheating considerations.

My FTDX-560 (one big chunky tube tranceiver!) will provide (verified on a 
dummy load and calibrated scope) 380 peak output watts on 75 meters with my 
voice driving it.  On the other end of the spectrum, it barely manages 220 
watts out on 10 meters.  The finals are used, but not that used. This 
rolloff is typical for sweep-tube final amplifier rigs, but you will see 
less efficiency on 10 meters even with the venerable 6146 series in most 

I do have a Swan 700CX-SS16 with a NOS pair of 8950's, but have not yet 
restored it.  Should be interesting to see how it measures.  Too bad I won't 
be using it often due to the absurd replacement cost of the finals nowadays. 
Besides I prefer AM/CW rigs.

So I'm not sure generating a comparative list based on output power is going 
to be that accurate or useful unless you can dig up actual lab or magazine 
review stats for each rig.

Mark K9TR

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