[R-390] R390 Filament Wiring

Bob Camp [email protected]
Sun, 06 Apr 2003 15:23:10 -0400


Hi,

In theory the R-390 was going to have a configuration in which it ran off of
28 volts DC rather than 110 volts AC. They put extra pins in the cable
harness and such to make this possible. The AC supply was going to come out
and a dynamotor plug in to the same location on the chassis. All of this
must have seemed like a good idea at the time since it justified adding
extra cost to every radio built.

The problem came when they tried to find a DC source that was quiet enough.
I suspect that the 28 volt DC supply was something of an issue all by it's
self. Once they got the dynamotor brushes into the act the RF noise went up
quite a bit. A big spinning dynamotor must have shook the chassis a bit as
well. Conventional wisdom is that they tried the trick on a couple of
radios. Once they tried to use them in this configuration they gave up on
the project and just ran them off of 110 instead.

By the time the R-390A came along the whole idea was long dead. That allowed
them to wire the filaments in a little more conventional fashion. It also
lead to the development of the R-392 which is a pure 28 volt radio. Given
that the 392 is a tuned IF radio rather than mechanical filters I tend to
look at it more as a 390 clone than as a clone of the 390A. If you look at
it that way then the 392 is the box that goes where a 28 volt 390 would have
gone.

Quiz time - does any of that make sense ?

    Take Care!

        Bob Camp
        KB8TQ



----- Original Message -----
From: "Michael Young" <[email protected]>
To: <[email protected]>
Sent: Sunday, April 06, 2003 2:49 PM
Subject: [R-390] R390 Filament Wiring


> Does anyone know why the military chose series wiring for the filament
chain
> in the R390?  Does the R390A use series or parallel wiring?
>
>
> TNX
>
> Mike
>
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