[TMC] GPR90-RXD Receiver & SSB

[hammadv at comcast.net]

HI John,

          Can you provide some further description of what you did for those of us who have the TMC.  My GPR-90 is up for complete rehab following finishing of my SX-101A, and I would love to add such a performance enhancer to one of the most beautiful receivers built.  

Kurt   K9ZWY

-------------- Original message -------------- 
From: John Poulton <jp at cs.unc.edu> 

> Mark, and group, 
>snip> 
> You can find details about this PD in the manual for the late production 
> GPR-90RXD's, available from Robert Downs. If anyone is interested, I 
> could write up what I did, which was obvious: I replaced the BFO tube 
> with a 6BE6, and did a bit of rewiring with a few odd added components. 
> I even managed to find one of the elusive Carling DPDT's. In England. 
> 
> The product detector "mod" works pretty well. You can copy CW very well 
> at full RF gain. I found it necessary to back off the RF gain a bit to 
> copy SSB, as the PD still doesn't have quite enough injection, but it 
> works reasonably well in that mode, too. 
> 
> A GSB-1 is a good, though spendy, solution; a CV-591/MSR, even better. 
> 
> BTW: the radio I described above is for sale; if anyone's interested, 
> be happy to provide details about it. It's a beauty! 
> 
> 73, John K4OZY 
> 
> On Sun, 14 Dec 2008, 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. 
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