[R-390] SERIAL # 163

[Graham Baxter]

It may have already been suggested but isn't this the Captain Paul Lee
product detector mod? I recall that the HT current which feeds the BFO was
used to energise a relay which switched the audio from the AM detector to
the product detector. This saved one having to change the switch.

Graham Baxter
G8OAD

2009/4/2 Gene Beckwith <W8KXR at neo.rr.com>

>
> *Gents,
>
> I have a recently acquired Motorola...has relay non-stock...not sure yet
> why . . . it's not a hack job...
>
> Did general up dates...caps etc...works great...didn't check out why or
> what the relay does..it's just behind the BFO pitch control inside the
> the filter deck...unit still has a live ballast tube...and is in
> pristine conx....label on rear says Army Security Agency...no other
> history...
>
> 73,
>
> Gene
> W8KXR*
>
>
>
> Flowertime01 at wmconnect.com wrote:
> > Richard,
> >
> > You own what you own and there is a relay in the BFO circuit.
> >
> > Accept that this is not original and it is not stock.
> >
> > As you have a serial number 163 and no one else has seen any of its
> brothers,
> > accept that what you have is not some spook modification, because you
> have
> > either the 163rd or 63rd one in the series. And again we have none other
> like it.
> >
> > There be only one R390 with manual and one R390/A with manual. The R390's
> > were mostly  built by Collins. R390/A were built by every one and even Al
> Gore
> > claims to have had a hand in the early contracts.
> >
> > Mods may have been for either inboard or outboard changes. Likely BFO
> mods
> > were for SSB.
> >
> > Grab a R390/A schematic and start doing a wire by wire pin by pin study
> of
> > the BFO tube and circuit. You will find where the relay was inserted into
> the
> > circuit.
> >
> > As we Fellows are not familiar with BFO relays, Where is your critter
> > actually mounted into the receiver? On the IF deck or some where on the
> front panel.
> >
> > I accept the relay looks like mil style. It would have the right voltages
> to
> > operate with the receiver. Is the relay coil about 220 volts B+ or some
> other
> > voltage?
> >
> > The BFO operated on switched 220 volt B+ to the BFO tube switched by the
> BFO
> > switch. If the relay coil is 6.3, 12.6, 24, 28 volts then the BFO switch
> has
> > been rewired from B+ to the coil voltage. But 200 Volt relay coils do
> exist in
> > mil style, so I can see one of those type relays being used.
> >
> > I can see that as the relay is energized, something switches the a load
> onto
> > the B+ line and drops the B+ to low for the receiver to work. Check the
> > schematic, pick a B+ point on a RF deck tube and another IF deck tube and
> see how
> > much the B+ drops when the BFO is switched on. If no drop go looking for
> the
> > problem else where. If the B+ drops 10 or more percentage start tracing
> the
> > circuit around the relay.
> >
> > Good luck with this problem.
> >
> > No reason you cannot restore the receiver to original and operating
> condition
> > with or without the modifications as you chose.
> >
> > Believe the schematic you have in hand is good for original and there is
> no
> > @@@RARE@@@ schematic out here some where you need to find.
> >
> >
> > Please do some digital photos if you can and save some hand drawn
> schematic
> > if you can. Yo may just snap some pictures and have a digital disk done
> when
> > you get them developed. You could then sent that disk to a Fellow here on
> the
> > reflector that could get the pictures up on a web site for us all to
> view.
> >
> > Someone put some thought and work into getting that modification into
> your
> > receiver. It may or may not have ever worked. But it could lead to some
> real
> > insight and spark of creativity. A good SSB detector for the R390/A is a
> much
> > sought after grail.
> >
> > Roger L. Ruszkowski AI4NI
> >
> >
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