I had plenty experience with GRA-53 transceivers. They are very proficient in cremating themselves. Unauthorized fans on the outside of the cabinet helped a little. The worst were ARC-27s used in GCA trailers. They cooked themselves so badly everything inside was dark brown. Is the SRC-20 amplifier a linear or does it have a modulator driven by the exciter?  Near the end of my term in the Air Force, we got some VHF transmitters that used a 10 watt AM exciter to drive a one tube linear to make 40 watts. Linear amps and AM are so inefficient. GRC-27s were huge and heavy, but were plate modulated and put out a good signal.

   B. Gentry, KA2IVY

On 3/30/25 7:00 PM, Jim Whartenby via Milsurplus wrote:
I would say that the URC-9 is similar to the VRC-24 in that both are UHF Transceivers and that the modules look to be similar but the modules are not interchangeable, specifically the PA module.  Now the TRC-68, GRA-53, GRA-54 and the VRC-24 all seem to have the same modules, but I never worked an the VRC-24 which is a 28 volt DC powered unit.  

When I was in the Air Force, stationed in the Philippines, I worked on the TRCs and GRAs.  They ran so hot that one had to wait half an hour for the R/T unit to cool off before you could carry it back to the shop.  Fun times! 

The URC-9 was Navy equipment and they never seem to buy "off the shelf", they always have to change things!  <grin>  The URC-32 vs the KWT-6 Type 8 is another example.
Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy


On Sunday, March 30, 2025 at 04:56:21 PM CDT, [email protected] <[email protected]> wrote:


More info below:

https://www.navy-radio.com/xmtrs/src20.htm

 

 

From: [email protected] <[email protected]> On Behalf Of [email protected]
Sent: Sunday, March 30, 2025 4:54 PM
To: 'Gary Hitchner' <[email protected]>; [email protected]
Subject: Re: [Milsurplus] 400 MHz cavity

 

Gary,

The cavity amp you have was part of the Collins AN/SRC-20.  The transceiver/exciter is the AN/URC-9, also known as AN/VRC-24.

It is a nice amp that can be easily tuned to 432 MHz.

Best, Francesco K5URG

 

From: [email protected] <[email protected]> On Behalf Of Gary Hitchner via Milsurplus
Sent: Sunday, March 30, 2025 2:50 PM
To: [email protected]
Subject: [Milsurplus] 400 MHz cavity

 

List,

I have two of these which are going to scrap unless someone tells me there is a reason not to.  (Or picks them up local).  Large and heavy.

These are a 225- 400 MHz cavity that used 2- 4CX250k’s in parallel, evidently  conversion to 432 was possible, but a project.  Fair Radio might have had them in stock for a while, or maybe Skycraft, not sure.

Often wanted to see the entire assembly these were in, must be something to see………….

Gary

WA2OMY

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