[TMC] GPR-90RXD stuff

[George Maier]

Very interesting Roy, thanks.  I have not noticed that particular hiccup yet, but I'll definitely keep an ear on it.  If the issue does pop up down the road, I'll definitely do a deep dive into the cause.   As I mentioned, the BFO injection point on the GPR-90RXD is quite different from the civilian GPR-90 and the commercial GPR-90RX, and that may have a bearing on the BFO behavior. 

Sorry to hear about the fate of your GPR-90; sad indeed.

TNX & 73,

George - W1LSB


-----Original Message-----
From: Roy Morgan [mailto:k1lky68 at gmail.com] 
Sent: Friday, August 06, 2021 1:57 AM
To: George Maier; tmc
Subject: Re: [TMC] GPR-90RXD stuff

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
> 
> 
> 
> 
> 
> 
> 
> 
> 
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