Caution re: Collins gear and relay racks

Discussion in 'Amplitude Modulation' started by K4KYV, Oct 3, 2019.

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  1. K4KYV

    K4KYV Subscriber QRZ Page

    If you are thinking of mounting a piece of rack-mounted Collins equipment into your station rack...

    I have a near-basket case 75A-1 that I wanted to store in an empty space in one of my 6' racks. I sold the original Collins cabinet because it was too bulky and heavy, and I don't feel like trying to get the rcvr running any time soon, even though it should still be restorable.

    Turns out the damned thing is just a hair too wide to fit into any of my standard open-frame relay racks. It would slip into a Bud cabinet in my shack, but that one is already filled. Apparently, Collins didn't care whether or not their gear would fit into anything other than the rack or cabinet they sold to go with their equipment (or perhaps it was intentional). Maybe that's why empty Collins rack cabinets fetch as much money as they do. The A-1 would probably fit if the side braces were removed, but the chassis is way too flimsy for that, so for now it's sitting on top of one of my shelves.

    If anyone has a use of the thing and would like to restore it or just to use for spare parts, let me know. I would trade or sell it cheap (preferably trade), but it will have to be pick-up only. I won't try to pack and ship it; not worth it to me. It sat on my table a couple of years ago at Dayton for both days, no takers.
    N2EY likes this.
  2. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    How new is your rack?

    It has been my experience that the newer racks are a hair narrower than those made in the 1930s and 1940s.

    The 51J- series / R-388- series all used the same chassis width, same braces, and same basic front panels as the 75A-1 through 75A-3. The 51J- / R-388- were sold for rack mounting with cabinets an optional, additional cost item. Thousands of those receivers were mounted in racks without any problems.

    The 75A-1 does have a different cabinet from the 75A-2, 75A-2A, and 75A-3. It uses the same cabinet as the 32V- series transmitters being that the 75A-1 is 7/8ths-inch deeper than the later 75A- series receivers.

    Look carefully at the machine screws that attach the brackets to the chassis. It is possible that they have been replaced and that the heads are thicker than the originals. Replacing the screws with some having thinner heads may solve your problem.

    However, although they definitely fit a 19-inch relay rack, none of the 75A- receivers were sold to be rack mounted! They all came with cabinets.

    Glen, K9STH
    K0UO likes this.
  3. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    Are the top and bottom cross members welded on or bolted? If they're bolted, you MIGHT be able to loosen the bolts and slide the rails apart just a smidge. (Be sure to tighten the bolts back up!) We had to do this in the central office where I worked for a while, after ordering some European racks.
  4. K5UJ

    K5UJ Ham Member QRZ Page

    I think some racks are tapped with different thread pitch or count. It's not standard. But that doesn't sound like the problem here. I learned a little trick from K9YQQ, one of those duh why didn't I think of this? kind of things: If you have a panel and chassis and no side braces, get a rack shelf and put it in upside down. slide in the chassis on top of it and bolt it in or it can sit if the rack is level. the 75A-1 might fit sitting on a shelf with the side braces off.
  5. K7JEM

    K7JEM Ham Member QRZ Page

    I have seen the same thing with lots of newer LMR stuff. Mainly a problem trying to fit it into older steel racks, but will fit fine in newer AL racks. I don't think there is a standard as far as the inside dimension between the rack. I know at one of our remote sites that was using surplus steel racks, we actually ended up cutting part of the rack to accommodate a newer Motorola radio, I think it was an MSF5000, but it would not fit into the steel rack at all, due to the width. Screws lined up perfectly.
  6. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    The old Western Union standard for relay racks had the mounting screw holes in groups of 2 with a larger separation between those groups.

    However, for decades, the Motorola rack cabinets had the mounting screw holes evenly spaced along the entire mounting rail. When used with regular rack mount equipment, there would be gaps between the panels instead of fitting closely together.

    Since I was, basically, associated with Motorola for all but 3-years during the 1965 through 1980 period, I obtained a number of rack cabinets for various projects. But, unless I was racking Motorola equipment, the panels did not always fit together!

    Glen, K9STH
  7. K7JEM

    K7JEM Ham Member QRZ Page

    Most of the Motorola cabinets had only holes, and "tinnerman nuts" had to be added to make their screws fit, IOW, the rack was not tapped for a screw. Most other steel racks use 10/32 type screws, and AL racks use 12/24 screws. The earlier Mot cabinets used larger coarse pitch screws, and newer ones use metric screws, around M6 in size. But all Motorola rack mount equipment will fit into standard racks (as long as the inside width is correct), and standard rack equipment will fit Mot racks, as long as the tinnerman nuts are positioned correctly, AFAIK.

    GE did the same thing with their cabinets. I think there was probably some advantage to not having to tap all of the holes, maybe saved some money somewhere. It also allowed the equipment to be moved slightly up or down, since the clips had a little play in them.
  8. KA9JLM

    KA9JLM Ham Member QRZ Page

    My 75A-3 would fit in a 19 inch Equipment Rack if put on rails.

    It is a bit heavy for a Relay Rack.
  9. WA3VJB

    WA3VJB Ham Member QRZ Page

    This is an excellent tactic to use when racking heavy gear.
    From experience:
    The R390 receiver, and its younger sister the R390A, are far easier to mount in a rack if you first mount an empty upside-down shelf as close as possible to the desired location. This lets you grunt the receiver up to altitude and slide it into place. Then, using soft tools as levers (wood slats, stiff plastic that won't mar the panel), you can raise the receiver up to the rack holes and begin mounting it permanently. The bottom rack screws first, then work your way to the top. Remove shelf when complete.

    KD0DQZ likes this.
  10. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Most of the Motorola racks did have the larger, non tapped, holes that used the "Tinnerman" clips. However, once in a while, a cabinet would show up with tapped holes. Since there were no obvious manufacturers' marks on the cabinets, I have absolutely no idea as to the source.

    Glen, K9STH

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