[Amps] SB-200 Output Power Too High?

[Mike Selfridge <scifiguy@starband.net>]

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.  40 and 80 meters also produce similar power, but 
with full 100W drive.

Now, before I hear that my power meter must be bad or out of calibration, 
let me say that the meter is new, and reads the same as my backup meter, as 
well as reading exactly what it should with my FT-897 (reads the same as 
the test data on the calibration sheet from Yaesu, within a couple percent).

I checked the output on all bands, using a spectrum analyzer, and found 
nothing unusual, so I know it is not producing parasitic oscillations, nor 
is the harmonic content too high.  On the air, I have had nothing but 
positive reports.

I know you can't get something for nothing, and class B amplifiers don't 
operate at 93% efficiency (yup, that's what I calculated), so I assume the 
meter on the front of the amplifier must be inaccurate.  I suspect the 
plate current and/or high voltage is higher than the meter shows, so I'll 
have to calibrate it with a current source, and replace the appropriate 
components to give an accurate reading.

Has anyone else with an SB-200 seen output this high?  My web searches show 
that most get about 600W CW.  I don't push the output to the limit on CW 
operation, but I love the ability to get 1100W PEP on SSB!

73

--Mike (N6QG)

_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps