[TMC] GPR-90 Redesign

[Dave McDonald]

Hi Chris,

I have both items also.  The only things that I have had to replace is the 
audio gain controls on both units plus the electrolytic in the GPR-90.  I 
did have to clean the band switch contacts with DeOxit.

The receiver is very stable and after warm-up, no drift.  This applies to 
the BFO also.  Once warmed up, copying SSB is a cinch.  The GSB-1 does well 
also but has a very narrow bandwidth so the audio is better using just the 
receiver.

No parts have "failed".  No tubes have been replaced, only the #44 pilot 
lamps.

I reviewed the circuit changes and couldn't find any reason to make the 
changes.  If you look carefully, you will find another set of antenna coils 
and switch wafer was added for that RF amp.  You would have to replace the 
entire band switch and add the mounting provisions for the added coils as 
well as the coils themselves.  That ought to give you enough reasons to 
leave it alone.

If it works, etc.

Enjoy the receiver.  It is the very best one produced during that era.  I 
have been through documentation on every tube type RX with dual conversion 
and 2 rf stages from the 50's and 60's, including the 75's, SX's, HQ's, and 
NC's and none approach the quality of construction and parts used by TMC. 
Others may have their little gripes but most who have spent any time with 
the GRP know what I am talking about.

There aren't many similar receivers playing today, 55 years old, can stand 
up to the GPR-90.  I thank TMC for producing it.  I am fortunate in that I 
am the second and last owner of this one and it was stored covered by the 
first owner and in showroom condition.

Enjoy es 73,

Dave
K4EWC


----- Original Message ----- 
From: "Chris Kepus" <ckepus at comcast.net>
To: "'Dave McDonald'" <jdmcd at ij.net>; "'Richard Knoppow'" 
<1oldlens1 at ix.netcom.com>; <TMC at mailman.qth.net>
Sent: Saturday, August 25, 2012 11:29 PM
Subject: RE: [TMC] GPR-90 Redesign


> 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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