[TMC] GPR-90RXD stuff

Fri Aug 6 17:01:24 EDT 2021

Just for the heck of it, I looked up the drawing for this coil (L38, BFO
output coil).  From the parts list, it's TMC part # CL-231, which is also
the TMC drawing number.

Here's the drawing URL (I've scanned most of the drawings for smaller coil
assemblies):

https://tmchistory.org/tmc_drawings/drawings_db/cl/cl_200_299/cl-231.pdf

The drawing is singularly unhelpful.  It shows a 3-rank pi-wound coil with
an inductance of 585uH (in agreement with the schematic, but not the parts
list) with a powdered iron core, but it doesn't even mention a tap or
indicate where it might be..  Arghhh.  Maybe the wire type and Q will be
useful to you.

Chris, hope you're able to find a photo of the coil.  I'd be interested to
know what you find out from it.

73, John K4OZY

On Fri, Aug 6, 2021 at 2:21 PM Chris Bolkan <bolkyboats at gmail.com> wrote:

> Hi George,
> Thank you! I would appreciate that pic and yes just email directly.
> I will look again, but I am pretty sure it is not there because I
> traced it all out and ended up capacitively coupling the BFO signal
> into the IF. Would be awesome if I am wrong! My goal is to make the
> receiver original, and then like everyone else, find an SSB adapter. I
> am looking for one of the rack mount adapters though because that is
> how I will ultimately mount the receiver.
> Best regards,
> Chris
> KI7NXY
>
> On Fri, Aug 6, 2021 at 11:11 AM George Maier <GeorgeW1LSB at verizon.net>
> wrote:
> >
> > Hi Chris:
> >
> > I'm happy to send you a photo, but not sure it will get through the
> reflector, so I'll send it to you directly.  Meanwhile, I suspect that the
> inductor you are seeking (assuming it's L38) may not missing, but is
> located far from the BFO.  In my radio, L38 is between pins 5 and 6 of the
> 8 pin accessory power out octal socket on the rear panel while the tap goes
> to pin 7.  The 3 pf BFO coupling cap, C59, is connected between pin 6 of
> that socket and pin 7 of the 6AL5 detector.
> >
> > Hope this helps!
> >
> > 73, George
> >
> > -----Original Message-----
> > From: Chris Bolkan [mailto:bolkyboats at gmail.com]
> > Sent: Friday, August 06, 2021 1:13 PM
> > To: George Maier
> > Cc: tmc collector's group
> > Subject: Re: [TMC] GPR-90RXD stuff
> >
> > Hi George!
> > I am a new member too and I also have an RXD. Mine is missing the tapped
> coupling inductor between the BFO and where it connects to the IF (at least
> according to the schematic I have). If you could take a picture of yours I
> would really appreciate it. I need to see what it looks like so I can
> figure out what I need to make to take its place.
> > This group is amazing and very helpful.
> > Chris
> >
> > On Thu, Aug 5, 2021 at 7:00 PM George Maier via TMC <tmc at mailman.qth.net>
> wrote:
> > >
> > > Hi All:
> > >
> > >
> > >
> > > I'm a newbie to the TMC list, but an old timer in the hobby; first
> > > licensed in 1958 as KN1GXT and K1GXT a year later.  The current call
> > > sign was pretty much a mid-life crisis, but that was almost 20 years
> ago now.
> > >
> > >
> > >
> > > Regarding TMC, I've had lust in my heart for a GPR for decades, but
> > > never owned one until now.  It's a Canadian made GPR-90RXD (ca 1971
> > > vintage) that came with an original TMC cabinet and a matching TMC
> > > speaker.  John P tells me that this a rare find so I'm wondering if
> > > anyone in the group has seen any other Canadian made receivers.
> > >
> > >
> > >
> > > It's actually in very nice shape physically and works rather well
> > > after some TLC and a complete alignment.  I'm still cleaning it up
> > > here and there, and will probably have the cabinets repainted
> > > professionally provided the color can be matched accurately.
> > >
> > >
> > >
> > > Does anyone know the actual color chip that was used, or have the paint
> > > formula?   Also, the speaker grill cloth must be replaced so I'm
> searching
> > > through all of the web based grill cloth resources, but have not found
> > > a really close match yet.  My interior designer XYL has given me some
> > > of her fabric catalogs to look through, so may I'll find something
> > > there unless someone has a good resource.
> > >
> > >
> > >
> > > Last but not least, the BFO injection in this receiver was
> > > ultra-wimpy, making it barely useable on CW and a waste of time on SSB
> > > .  It's different from other GPR's in that the BFO is injected at the
> > > detector while other models have the BFO injected at the grid of last
> > > IF tube, except for the RXDS with its built-in product detector.  The
> > > RXD is actually more like most Collins, Hammarlund, Hallicrafters and
> > > National radios that do not have built-in product detectors, but their
> injection levels are much higher.
> > > Adding 20 pf to the original 3 pf BFO coupling cap made all the
> > > difference in the world; it's now a very pleasant receiver on CW and
> manageable on SSB.
> > > Score one for the old guy!
> > >
> > >
> > >
> > > Any info or tips will be sincerely appreciated.
> > >
> > >
> > >
> > > Thank & 73,
> > >
> > > George - W1LSB
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
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