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Re: [Amps] SB-200 Output Power Too High?

To: scifiguy@starband.net
Subject: Re: [Amps] SB-200 Output Power Too High?
From: wb8jkr@juno.com
Date: Sun, 7 Dec 2003 05:19:51 -0500
List-post: <mailto:amps@contesting.com>
  The highest output I've EVER seen from an SB-200 is 650 watts.

Mark  WB8JKR


On Sat, 06 Dec 2003 14:37:46 -0800 Mike Selfridge <scifiguy@starband.net>
writes:
> 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)
> 
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> 


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