[TMC] GPR-90 RXD vs RXDS

[Mahlon Haunschild]

I received my manual from Robert & did a quick compare.  Here's what I 
noticed:

- Per Richard's message, the "D" does indeed use a 6AG5 for the BFO, 
while the "DS" uses a 6BE6 in a much more complicated circuit (probably 
contained in the "can" that the tube plugs into).

-  The "D" does not have a hi-Z IF output, the "DS" does.

-  There appear to be minor differences in the rear apron layout.

-  On my "D", E1 terminals 1 and 2 are rubber-stamped "AVC IN and OUT" 
according to their function (no circuit differences that I can tell). 
The "DS" pic in the manual doesn't indicate these rubber stampings, but 
does correctly indicate a wire jumper bridging the terminals.  Note that 
the "D" schematic on the web site shows E1 as the receiver antenna 
input, with a 300 ohm/75 ohm balun behind it.  Mine has a BNC 75 ohm 
input only (same as the "DS" apparently).

-  My "D" has a BFO input jack on the rear apron; the "D" schematic on 
the web site doesn't show this.

-  My "D" uses the aforementioned 6DC6 & 6BA6 as the 1st and 2nd RF 
amplifiers, instead of the 6AB4 and 6CB6 that the "D" schematic on the 
web site shows.

I suspect that some of these changes were made as a general improvement 
across the GPR-90 product line since, for example, the 6DC6 and 6BA6 are 
newer tube designs than the other two tubes.  But that's a HUGE leap of 
faith on my part.  Others are going to need to pop the covers on their 
GPR90s to check this assertion out, since I only own one.

Still looking for a calibrator crystal for mine, by the way.  I suppose 
I could solder some FT-243 pins onto a crystal that I already have, but 
would prefer to have the genuine article.

regards,

Mahlon - K4OQ

> --__--__--
> 
> Message: 2
> Date: Sun, 11 Apr 2004 18:43:36 -0700 (PDT)
> From: "Richard M. MC Clung" <sgm460122@yahoo.com>
> To: tmc@mailman.qth.net
> Subject: [TMC] Re: TMC GPR-90RXDS
> 
> Look at the BFO/Detector circuit of the RXDS vs the other
> models and I think you will see the major difference. 
> 
> V13 in the RXDS is a 6BE6 used as the BFO and Product Detector.
> The HV rectifier tube is also replaced with solid state device.
> 
> The Diversity versions allow for HFO and BFO signals to be
> provided from a single stable source, such as a TMC VOX-5,to
> allow the receivers (2 or 3) who's AVC and Diode loads are also
> interconnected to operate as one receiver. 
> 
> RICH  WA6KNW