[TMC] GPR-90 Redesign

[Chris Kepus]

Hi Dave and Richard,
I have a GPR-90 and GSB-1 combo that I am getting ready to put back into
service.  They worked FB when "parked" five years ago.  Have either of you
had to replace any components that aged (hate to say failed) to the point
where receiver performance was degraded?  Any issues with drift?

I also have the 90RX schematic and I remember wondering if the RX front end
would be a worthwhile mod (less noise, more sensitivity).
 
Thanks for any comments one way or the other.

73,
Chris
W7JPG

-----Original Message-----
From: tmc-bounces at mailman.qth.net [mailto:tmc-bounces at mailman.qth.net] On
Behalf Of Dave McDonald
Sent: Saturday, August 25, 2012 1:26 PM
To: Richard Knoppow; TMC at mailman.qth.net
Subject: Re: [TMC] GPR-90 Redesign

Richard,

If you compare stage by stage, you will find other subtle changes.  These
were probably needed to control by external oscillators and crystals.  The
RF input change may have been required to satisfy the requirements of the
intended market which was government total HF coverage and not the amateur
market.

My GPR-90 stays on daily on the 22, 19 and 17 meter bands and I have never
seen any problems with the GG input.

73,

Dave McDonald
Clearwater, FL
K4EWC


----- Original Message -----
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: <TMC at mailman.qth.net>
Sent: Saturday, August 25, 2012 1:37 PM
Subject: [TMC] GPR-90 Redesign


>      I discovered from looking at the schematics that the
> RF stages of the GPR-90 were redesigned for the GPR-90RX.
> The original receiver has one stage of grounded-grid
> amplification coupled to a conventional pentode. The
> grounded grid stage is bypassed for the broadcast band.  The
> RX model has two conventional pentode stages on all bands.
> The tube chosen for the first RF is one that has good IMD
> performance and is pretty quiet. I wonder why the GG stage
> was eliminated.
>
>
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com
>
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