Like an idiot I removed the RF deck and the gears for cleaning/clamp replacement and now cannot get this back together working correctly! I tried to write this so it makes sense, probably will not. I do not know the formal name of each gear and the part numbers I refer to are from the r390a-063-2010-7004 pdf of NAVSHIPS Technical Manual. The problem gear I am talking about is the one shown in Step 2 of Chapter 10 (part #79/66 in the manual). It has a shaft with THREE gears on it (small pinion gear (#79); large brass gear with 4 hole cut-outs and another smallish gear (#66). Step 2 of Chapter 10 says “Insert it with the pinion meshing with the Geneva Drive gear”. So its shaft inserts into bushing M in the frame and the pinion (#79) meshes with the Geneva Drive gear. The problem is the next step; the large brass gear on this same gear assembly is I THINK supposed to mesh with “small gear” of the large 4 hole cut-outs brass gear assembly #42 (#42 is on the same shaft as gear assembly #63/64/65 that attaches to a different gear with three screws). When the pinion gear of #79/66 meshes with the Geneva Drive gear, the large gear on this assembly can BARELY reach “small gear” of #42; it almost completely falls out of its bushing. It is as thought #42 should “go back” more, but it can not. Am I missing something, is the large gear on #66 NOT supposed to mesh with the rear gear of #42?
From: Jacques Fortin <[email protected]> Date: Thursday, June 18, 2026 at 10:40 AM To: 'R390A' <[email protected]> Cc: [email protected] <[email protected]> Subject: RE: [R-390] Removing Megacycle Change shaft Hello Paul, I also have a spare of the right size clamp (13/32" hole - 0.406 in from the spec sheet) but sending it to the US became a big problem since... you know what. I also searched for a commercial source for these clamps (or any valid replacement) yesterday and failed to find anything suitable. The clamps used in the R-390 and R-390A were also used in some other Collins products of the same era, but they are not of "standard" dimensions, compared to the commercially available ones I have seen. There is four different size clamps in the R-390A. Not very hard to machine with the right equipment. One of this forum members already made one from "scratch", it was one for the knobs if I remember well. Having one that breaks is unlikely, except if someone greatly over-torqued the screw: the clamp broke instead of the screw...oh my. Your set was "overhauled" by a US Army depot, right? I will tend to inspect EVERYTHING within. And I really mean EVERYTHING. Canadian Army was not better: the worst case I run across was a substitution of the racks tuning slugs with some other of different origin, meaning different relative permeability, which rendered the set impossible to align properly. The whole radio was probably "junked" (sent to the surplus disposal), for that very reason. And yes, it is the 1st contract Collins that figures in the Gianni Becattini book. Paul, You mentioned that the R-390A is a "beast" compared to your Hammarlund radios. Your are lucky that it is not a R-390, which is a "beast and a half" ! 73, Jacques, VE2JFE in Montreal I have panel off and waiting for a gear clamp off a MC shaft assembly I just got on eBay. Going forward, is there a COMMERCIAL source who sells clamps that would work as gear clamps, (Bristol or hex or slotted) for other clamps that might break? Thanks for the help. I might need help with aligning this thing to read correct frequency when I am done, lots of gears! But I will read the literature and hope I get it. At least now that this is apart I can clean off the gears/gear teeth with isopropanol and “re-lube”. I assume just put light oil on the shafts themselves, not the teeth on the gears? Paul ______________________________________________________________ R-390 mailing list Home: http://mailman.qth.net/mailman/listinfo/r-390 Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
