>Question 1: The fan in my SB-220 starts making noise after several minutes
>of operation ...snip...
Oilite bearings need to be oiled. [see "Circuit Improvements......." in
the 11/90 QST]
>Question 2: When I work on the fan, I would like to add a switch to allow
>standby operation.
Technically speaking, there is no reason for a standby switch in the
SB-220. The filament transformer is a special current limiting type that
does not stress the instant-on filaments. You can switch a 220 on and
off as often as you like, without worry. However, switching one on
during transmit is not a wonderful idea, methinks.
>Is there a mod that changes out the rocker switches for
>a three position switch or any other good ideas.
A one-second delay auto step-start might be nice. The stock, lethargic
relay makes a good stepstart relay.
>I also want to add a
>circuit to control the relay from a low level supply as I DO NOT like
>bringing the relay return out to a solid state transceiver.
Agreed
>I would prefer
>to build the circuit rather than use one of the commercial boards for that
>purpose, but I guess an inexpensive one would work as well.
The circuit in Fig. 7B at http://www.vcnet.com/measures does this, as
well as converts the 220 to high speed switching so that it will not
RF-hotswitch with modern radios.
>Wendell Wyly W5FL w5fl@flash.net
Rich---
R. L. Measures, 805-386-3734, AG6K
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