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SB220 on six meters
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by kc1xu on November 15, 2001
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I am looking for information on converting an SB220 to six meters. Anybody know of any past published articles in QST or CQ?
Thanks and 73,
KC1XU
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RE: SB220 on six meters
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by n6tr on November 16, 2001
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There are a few references on the web that talk about making this modification. Also, one person offers a modification for a several hundred dollar price.
This first question you need to answer is if you want to maintain the HF capability of the amplifer (with the possible sacrafice of 10 meters). If the answer is yes, then you will be making a comprimise solution that won't be very efficient. When you deal with 50 MHz, it is difficult to allow for bandswitching without loss. The better decision is to decide to make the amplifier work for six meters only - and change some of the key components to be consistent with a 50 MHz amplifier. This would include things like the filament choke, HV plate choke, parasitic suppressors and the input circuit. Removal of the bandswitch will allow for sufficient reduction of inductance and stray capacitance that you should be able to make a final tuned circuit by winding yourself a small 2 or 3 turn coil out of copper. You can check the output cicuit by using an SWR analyzer and a resistor to simulate the output impedance of the tubes. In short - there are a lot of things you can go read about in the ARRL handbook - and then actually implement in the amplifier. I did a similar conversion myself and was very pleased with the results. I have 1500 watts output with a pair of 3-500Zs with 100 watts of drive. Doing a modification like this doesn't require a lot of mechanical modifications - and is very rewarding when it all works. I can provide answers to specific questions if that helps you ([email protected]).
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RE: SB220 on six meters
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by K8CC on November 20, 2001
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I used to have a SB-220 on 50 MHz that worked very well. The details of the mods to accomplish it are on my web site at this URL:
http://people.mw.mediaone.net/k8cc/
When driving it with a IC-756, 100W in yielded 1000W out and the tubes would barely show any color.
73,
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RE: SB220 on six meters
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by ny1e on November 21, 2001
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The origonal conversion was in QST hints and kinks, December 1974. it converted 10m to 6m. I did it and it worked well, I latter converted compleatly to 6m with vaccum variable etc. and saw little further improvement. GL de Dick NY1E
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