On Tue, 22 Sep 1998 16:37:02 Scott Townley <nx7u@primenet.com> writes:
>
>I believe I've devined from the old ads that the National R-175 plate
>choke
>was pre-15m and the R-175A was redesigned for post-15m bands.
>The question is (if I've gotten my history right), how do you tell the
>difference? I've got a basket case amp with one or the other, but
>either
>the p/n has faded/rubbed off/whatever or they didn't mark their parts.
>Any physical clues as to differentiating? Thanks!
The parts were not marked.
Anyway, the easiest way to tell the two apart is to look at the top
section. The 175 is continuous wound while the 175A uses a split winding
midway.
The 175 can be modified by rewinding the top section.....ONLY.....as
follows AND with the original DSC wire.
Wind exactly 1" of wire, then a 3/16" gap and then exactly 1" again. The
175A is also rated for 6M.
A rather interesting ad can be found in May 1954 QST, a bit humourous but
also informative.
73 Carl KM1H
National Radio 1963-69
>------------
>Scott Townley
>nx7u@primenet.com
>------------
>Collector of:
> Stoddard Aircraft EMI/RFI receivers and accessories
> Big Parts for that Big Linear Amp
> 70's era RF test equipment HP/GR/Tek
> Radio-related technical reference material 1940+
> ...anything else that will keep me off the streets at night
>
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>
>
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