[TMC] GPR-92

[John Vendely]

The GPR-92 had a tuned 1st RF stage, more like the GPR-90RX and RXD, 
whereas the GPR-92A had the broadband transformer-coupled grounded-grid 
1st RF stage similar to the basic GPR-90.  The grounded grid versions 
were cheaper to produce but, like the GPR-90, these receivers had 
strikingly poor image rejection and intermod performance.  The GPR-92 
series apparently did not sell well and was discontinued after just a 
few years.  The GPR-90RXD, however, was still listed in the 1968 TMC 
catalog, though it seems unlikely many would have been sold at that late 
date.  I recall hearing the same thing JP mentioned in an earlier 
email--that the GPR-92 was not considered to be quite as good as the 
GPR-90.

TMC's next general purpose receiver design was the completely 
solid-state GPR-10, a general coverage version of the extraordinarily 
complex and expensive AN/URR-64 (DDR-10) developed for the U.S. Navy.  
Only 6 engineering prototypes were built in 1968, and work on the GPR-10 
was discontinued in early 1970,  by which time GPR-110 development had 
begun.

TMC seems to have bought the Mackay 3020 for resale, listing them for a 
time in their catalog.  It may originally have served as an interim 
offering while the GPR-110 was under development.  The GPR-110 
eventually made it into limited production, but its complex (though 
interesting and sophisticated) frequency synthesizer design proved 
unreliable.  As a result, TMC ended up buying back most GPR-110s.  In at 
least one case they were obliged to replace a customer's GPR-110s with 
purchased Mackay receivers, probably 3020s.  I do not know how many 
GPR-110s were produced, but it can't have been many.  I know of only one 
person who has one and, needless to say, it is non-functional.

73,

John K9WT


On 3/24/2021 4:30 PM, Richard Knoppow wrote:
> Yet another interesting TMC receiver is the GPR-100. I downloaded the 
> instruction book our of curiosity and recognized it as the same 
> receiver as the MacKay Marine 3020. There is a similar MacKay 3030 
> which looks very much the same but is probably a later model. I had 
> thought that all MacKay Marine equipment was made by Federal 
> Telephone, another ITT company but evidently not. I also got the 
> instructions for the TMC GPR-110 but it seems to have been designed 
> for general purpose rather than maritime radio use. Again, I wonder if 
> anyone has either set and, if  you do, what your opinion of them is.
>    A note on the GPR-92, TMC seems to have gone back to the grounded 
> grid first RF it used in the original GPR-90. The diversity version, 
> the GPR-90 RXD has a more conventional pentode RF plus a re-designed 
> BFO. The reviews of the GPR-90 say the BFO pulls, surprising in any 
> "modern" receiver. I did not look at the BFO in the 92, which in 
> general is quite different from the 90 but evidently the GG RF stage 
> was thought to have enough advantage to go back to it. From a design 
> standpoint the 92 is a very interesting receiver.
>    I rather think the GPR-92 was intended to provide a house built 
> receiver to avoid the Hammarlund SP-600 in diversity receiver systems. 
> TMC seems to have used Hammarlund receivers modified by Northern 
> Radio. Eventually, Hammarlund produced the -17 which has all the 
> diversity mods except for a gain trimmer, which could be added later. 
> I think someone at Hammarlund was just asleep at the switch.
>     You are all aware I am sure of the Hallicrafters version of the 
> SP-600, Didn't quite make the grade although Hallicrafters did address 
> the problem of drift from unregulated filaments.
>    Oh, enough meandering.
>
> On 3/22/2021 3:15 PM, W2HX wrote:
>> Mine:
>> https://w2hx.com/x/TMC%20Technical%20Materiel%20Corporation/GPR-92-SBE-2-PMO-5/GPR-92.JPG 
>>
>>
>>
>> -----Original Message-----
>> From: tmc-bounces at mailman.qth.net <tmc-bounces at mailman.qth.net> On 
>> Behalf Of Richard Knoppow
>> Sent: Sunday, March 21, 2021 4:36 PM
>> To: tmc <TMC at mailman.qth.net>
>> Subject: [TMC] GPR-92
>>
>>      Not any traffic here lately so I will drop a rock into the pool.
>>      I am curious about the GPR-92. Does anyone actually have one?
>>  From what I've read not many were built. Evidently they were 
>> difficult to make and performance may have been partly wishful 
>> thinking. They are so sexy looking one wants them to be extra good 
>> but I think it was a miss rather than a hit. There is probably stuff 
>> in the list archive but I have not looked.
>>
>