[AMPS] SB220 power output

[measures]

>
>Let's see if I can ask a question that is a bit more specific this time.
>I am about to visit the owner of this SB220 that I am considering the
>purchase of, and I'd like to conduct a test that will give me a sense of
>whether the finals and power supply are in reasonable shape or not. 

The most common failure is a grid/fil. short.  This is caused by a bent 
filament helix.  The only way of telling when a short is immininent is to 
test with a high-pot.  Good tubes have a breakdown V of 6kV or more.   
4kV or less means the filament is bent.  

>A simple test that I would think would be telling would be of the form:
>
>(1) operating on ffff frequency
>(2) amplifier terminated into a 50 ohm dummy load
>(3) with X watts CW drive power
>(4) amplifier properly tuned
>(5) the output with the switch in CW position should be about Y

Around 900w.  Plate current should be >700mA.  Emission is typically ok 
in 220s because of not excessive fil. V.  

>(6) and in the SSB position should be about Z
>
An accurate SSB / PEP measurement requires test equipment that most hams 
do not own.  

>Presumably drive power level would be chosen to maximize amplifier
>output, at least for this test measurement.
>
>I understand that this would not necessarily mean I can operate at that
>power level, due to the various (mainly heat) issues that were raised in
>response to my first question. 

The SB-220 has a clearly superior cooling system -- provided that the fan 
bearings are routinely oiled every 1000 or so hours.  

cheers, Bill

-  Rich..., 805.386.3734, www.vcnet.com/measures.  
end


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