>I have a very well kept Heathkit SB-200 I purchased a couple months
>ago. It has the Harbach power supply, soft start, and soft key mods. I am
>running it on 240VAC (measures 232VAC when keydown). The tubes are new
>(about 20 hours) Taylor 572Bs.
>
>Before buying the amp, I had read that the SB-200 can output about 500W to
>700W CW, with 100W input. However, much to my surprise and delight, this
>amp puts out a lot more.
>
>The highest output seems to be on 20 meters, where it actually achieves
>1100W CW into a dummy load (found this out by accident, when I drove it
>with 100W, then noticed the plate current was way too high, so very quickly
>reduced the drive). At 70W input, the plate current reads 500mA, and the
>output is about 900W CW. ...
** The emissive limit of two 572B for linear applications is c. 440mA.
Drive requirement for linear is c. 35w per cathode. Before believing Any
wattmeter, measure R with an digital ohmmeter. The most accurate check
is to measure the peak V across the measured R with a freshly calibrated
oscilloscope, and do the arithmetic. A good rule of thumb is that if
your amplifier has over 110% efficiency, your wattmeter just might need
to be calibrated.
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