[TMC] GPR90-RXD Receiver & SSB

[Rodger]

Mark,

I have one I acquired early this past summer.  Mine also needed a few 
capacitors and an alignment.  After that it works fine on AM....

I really don't think this receiver was designed to be used on CW/SSB 
without its external SSB converter.  Like you I found the BFO injection 
is minimal and you probably have also noticed the tendency for the BFO 
to sync with strong CW signals.  I imagine increasing the coupling 
capacitor made it even worse.  This tendency was noted when the receiver 
was new and reviewed (in QST as I recall).

Later in the summer I found a Hammarlund HC-10 sideband adapter at a 
hamfest (at $40 it was a great buy!) and paired that with the TMC 
receiver and that turns the GPR into a fine receiver for SSB and CW.  I 
haven't found any drift or stability problems with my GPR-90 so the only 
problem was in the detector.  If you could find the matching TMC SSB 
converter that would probably be a nice performing and great looking 
setup also.  The HC-10 is basically the final 60 Khz. IF and product 
detector out of the Hammarlund HQ-170/180 series so it does a very nice 
job of providing tight selectivity and detecting CW signals.  I also 
tried a Central Electronics sideband slicer which are commonly found and 
it provides a tremendous improvement although not as much as the Hammarlund.

So, if you want a nice band cruiser that is also very good for AM ham 
operation the basic GPR-90 works fine.  Adding an external SSB converter 
also turns it into a very nice SSB and CW receiver.

Basically I would call it a well constructed receiver that looks great 
but definitely has an issue with its BFO/detector.  Of course a lot of 
the "legendary" receivers have issues.  I have an National NC-400 with 
its interesting dual IF strips and it is a fine receiver except 
stability is marginal on the highest frequency ranges (I believe in 
typical operation it was used with an external control oscillator).  My 
Hallicrafters SX-88 looks great paired with my Johnson Ranger/Desk KW, 
has wonderful 250 hz CW selectivity, great audio, and generally works 
very well.  However, the much cheaper SX-100 and SX-101 series with the 
switched selectable sideband are much easier to use on AM when QRM moves 
in from one side or the other; to get the same effect with the SX-88 you 
have to retune instead of just switching sidebands. 

In summary, I wouldn't call the GPR-90 a huge disappointment but the 
looks greatly exceed the performance on CW/SSB.  But mine spent several 
weeks working AM and CW paired with a Viking 500 while I was repairing 
the Pierson KP-81 that normally goes with the Viking 500 and I was 
pretty happy with its performance.  It sounds like your receiver is 
working normally for a GPR-90.

73, Rodger WQ9E

Mark Johnson wrote:
> I recently acquired a GPR90-RXD receiver and did a pretty thorough 
> overhaul and alignment. I replaced some weak tubes, a few leaky 
> capacitors and as mentioned, I then did a very thorough alignment 
> using better than average test gear.
>  
> While the sensitivity is good and the receiver is OK, I find that 
> using it for SSB or even CW, it is not as good as other receivers I 
> have of similar genre. I have to back the RF gain control off to the 
> point where sensitivity suffers or it will overload. I increased the 
> value of the coupling capacitor from the BFO circuit and that helped a 
> bit but as mentioned, other receivers of similar genre are better even 
> though they, like the GPR90-RXD, don't have product detectors.
>  
> From the experience of others, is this common for this receiver?
>  
> Overall I have to say I'm disappointed with the receiver. I've had 
> many "Boat Anchor" receivers over the years and always wanted on of 
> these TMC receivers. Its no where  close to any of the Collins 
> receivers, R390's, 51j series, or even my RCA CR-91a.
>  
> What's the experience of others?
>  
> Mark V Johnson VE3DJU/VE3DDI
> ------------------------------------------------------------------------
>
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