[ARC5] ARC-5 Screws

[Mike Morrow]

Mac wrote:

> I guess the ARC-5 versions would need the black 
> and SCR-274-N stuff the nickel, right? 

Ken wrote:

> No. 
>
> Actually, there were a mixture of black and silver screws on the ARC-5 
> versions, at least. This was on the cover screws. There are several screws 
> (4?) that do not need to be removed on either side of the cover, just 
> loosened, to enable the cover to be removed. Others DO have to be removed.

Well, that's close.  

For all of the classic MF/HF command set gear, to remove *any* component
(cover, bottom plate, adapter panel, etc.) the associated screws must be
*completely* removed.  The only "loosen and slide" fasteners are on the
Western Electric VHF gear, especially the R-28/ARC-5.

The receivers use nickel-plate screws for:
1.  The front adapter panel (4)
2.  The bottom plate (14)
3.  The tube cover  (8)
    Note:  There are also 15 black screws on the periphery of this cover.
    ONLY the 8 plated screws must be removed.  The black screws do NOT need
    even to be loosened in order to slide the cover off.  This cover
    requires removal for any routine service that will align the front-end
    trimmer capacitors.  The 15 black screws are associated with the 
    tuning capacitor cover, whose removal would be very rare.

The transmitters use nickel-plate screws for:
1.  Antenna inductance cover plate (4)
    Note:  This applies to the AN/ARC-5 and late ATA units only.  Normal
    ATA and SCR-274-N units use slide fasteners instead of screws to
    attach this plate.
2.  The bottom plate (12)
3.  The tube cover (19).

The other components (modulator, racks, control boxes, jack boxes, antenna
relay, etc.) use nickel-plated screws to attach cover plates and tube covers.

Black-finish screws are used in locations that normal maintenance and operation
would not require loosening, such as those 15 receiver cover screws, capacitors,
relays, transformers, etc.

All screws should have an internal tooth washer around them.

> I think the 274N series were the same way.

True.  The ARA/ATA, SCR-274-N (regardless of finish), and AN/ARC-5 sets
all follow the convention described above.

It makes sense.  And it's a clue for determining that a ham may have tried
improving one of these units when this convention has not been followed,
assuming that more than one in ten screws have even been re-installed.

What doesn't make sense is why so many of these damned little screws were
used at all.  I mean...19 just for attaching the transmitter cover!  Oddly,
the sensible folks at Western Electric, which eliminated some of A.R.C.'s
worthless pre-war extravagance, did *not* get rid of this nonsense except
for its native design for the VHF sets (R-28 and T-23/ARC-5). 

> Dave or Gordon or Mike might have exact details.

I'm not the Mike to whom you refer, but I'll jump in anyway. :-)

Mike / KK5F