[TMC] GPR-90RXD stuff

Fri Aug 6 20:48:17 EDT 2021

Hi John!'
Yes, I've looked at the drawing. I've gone as far as I can in the
awesome TMC library, but the drawing is not sufficient to reproduce
the part, for instance where and how it is tapped. It's like that
drawing is a purchasing document, not an engineering drawing. I was
hoping for an engineering drawing.
But I am NOT complaining! The TMC library is absolutely amazing!
Regards,
Chris

On Fri, Aug 6, 2021 at 2:01 PM John Poulton <jp at cs.unc.edu> wrote:
>
> 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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