Isn't the ARC-2 perhaps the first Collins transceiver?  Also the first to have a hermetically sealed HFO later known as a PTO.  The ARR-15, an offshoot of the ARC-2, with it's RF slug racks, IF slug racks, two PTOs seems to me to be the start of the 51J except that the ARR-15 is single conversion  The 75A came later, AFAIK.
Jim

Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy


On Friday, November 1, 2024 at 04:12:45 PM CDT, [email protected] <[email protected]> wrote:


And very low power transmitter. 25 watts on a good day. 

On Fri, Nov 1, 2024 at 4:05 PM Hubert Miller <[email protected]> wrote:
The ARC-2 is a very strange beast with its varying IF. It was clearly thought of as a voice radio first, maybe as replacement for Command Sets. It's kind of a hassle to use on CW - there's no "BFO offset".
-Hue Miller



Sent from my Galaxy


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