>The 6E2L crew just finished an expedition to Baja California for the
>ARRL DX CW contest, and once again we ran into amplifier
>problems. We would like to obtain a couple of simple amplifiers,
>probably based on a pair of 3-500Z's, for these expeditions.
>We drive down by car, so portability is not a major consideration.
>The amps need to cover 160 - 10 meters, with a kw or higher output.
>We had good luck this time with an SB-220, but it does not cover 160
>in stock configuration.
>
>Can the SB-220 be modified for 10-160?
? yes. I wrote an article about doing so in the 1-89 issue of QST. The
original manuscript and drawing for the article are available at:
www.vcnet.com/measures
> (or even 15-160?)
This would be less easy than one might think. The problem is that the 160m
tune and load padders need to be switched in - and this can not be accomplished
without adding another bandswitch wafer, for which there is insufficient room.
>There seems
>to be a good supply of SB-220's available in the < $500 range.
This seems too cheap unless the tubes are shorted.
>Any other ideas? We don't want to spend a fortune on the amps, which
>will be pretty much dedicated to this application, and
>don't want any complicated control circuits or fragile grids.
The fragile grid thing is seemingly over-rated. When a grid is damaged by
parasitic oscillations, a unique pattern of damage results. {see photographs
in 9-90/10-90 QST article "Parasitics Revisited"} When a tube is overdriven,
the cathode is most commonly damaged.
cheers
Rich...
R. L. Measures, 805-386-3734, AG6K
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