[TMC] GPR-90RXD stuff

[Roy Morgan]

George,

Apologies for not snipping quoted text -

I lost my GPR-90 in a disaster some years ago, but remember one strangeness reported by others:

GPR-90 IF signal pulls the BFO near Zero Beat

A strong signal will pull the BFO, the beat note disappears close to zero beat as the IF signal and the bfo lock together. 

I don't remember a difinitive cause being reported but one suspected cause is that the strong IF signal was following a path to the bfo oscillator and causing it to lock onto the offending IF signal, possibly via filament or B+ wiring. 

Bypassing various points in the two circuits with a capacitor, or searching for the IF signal with an oscilloscope would likely find the culprit and suggest a cure. 

Roy Morgan
K1LKY Western Mass

> On Aug 5, 2021, at 10:00 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
> 
> 
> 
> 
> 
> 
> 
> 
> 
> ______________________________________________________________
> TMC mailing list
> Home: http://mailman.qth.net/mailman/listinfo/tmc
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:TMC at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html