[R-390] R390 Filament Wiring

[David Ross]

Bob & the gang -

  Bob's statements about the R-392 being a follow-on to the R-390 bring
to mind some thoughts about the R-391 & the GRC-19 set.

  The GRC-19 amounts to a R-392 paired with a T-195 -  the T-195 is a
Collins-designed 100W AM/CW/RTTY transmitter with eight Autotune
channels.  The R-392 is of course manually tuned.  What's the sense of
having an automatically tuned transmitter paired with a manually tuned
receiver?

  I'd bet that the GRC-19 radio set was originally intended to have a
'hardened' R-391 as it's receiver.  By 'hardened' I mean packaged like
the R-392 is -  watertight case with seals on all the knob shafts, that
sort of thing.  And it would use the DY-78/URR plug-in 28VDC dynamotor
power supply which was already available for the R-390.

  Having a suitably modified R-391 paired with the T-195 would provide
eight Autotune channels both transmit & receive.  Drawbacks of course
would be the size & weight of the hardened R-391.  The size of this
hefty R-391 version was probably what killed the idea -  doggone GRC-19
would be too large to fit in it's intended target, the back of an M-38
Jeep...

just a thought...
Dave Ross    N7EPI    ross@hypertools.com





Bob Camp wrote:
> 
> 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 ?
>