[David Dunlop]

A bit of a collective title to cover off several related receiver parts all at once.

The 52-Set Receiver uses two British Valve types (Canadian Equivalents) for the main operating chassis, factoring out the self-contained Crystal Calibrator sub-assembly. There are eight ARP-3’s and a pair of 12Y4A’s. Both of the sockets for these valves are of a brown, phenolic board design, rather than Bakelite, or ceramic.

HOLDERS, Valve, 5-Pin, on 1-27/32 inch centre mounting holes, ZA/CAN 4734, are used for the 12Y4A’s.

HOLDERS, Valve, 7-Pin, on 1-7/8 inch centre mounting holes, No. C1 ZA/CAN 4305, are used with the ARP-3’s.

Both of these Holders mount from the bottom, or back of the chassis, using a pair of truss head, 1/8-inch diameter by 5/16-inch long, soft steel, tubular rivets. Commercially today, these two valve sockets/holders are known as ‘5-Pin’ and ‘B&’ sockets respectively.

At the same time as the above two Holders get installed on the receiver chassis, a third part is also fitted to the top side, or front, of the chassis to be secured by the same two rivets coming up from behind the Holders. This part is as follows:

BASES, Metal, Shields Valve ZA/CAN 4524.

In the three photos attached, the 5-Pin Holders are on the left and the 7-Pin on the right, with the Bases below them with the rivets.

Removing these Holders and Bases was relatively straightforward. I used a large enough drill bit in my cordless drill to cover the circular crimped rim of the tubular rivet in the base mounting holes. With the crimp shaved down about half or so, I then took a 4-inch Common Nail, centred it on the hollow end of the rivet and gave it a whack with a hammer. The point on the 4-inch nail was just long enough to push the rivet out the chassis metal with no damage to the Base.

There was an interesting discovery about these two Holders as the rivets came out.

Both Holders are made up of a sandwich of two phenolic plates. The Pin Terminals are crimped onto the lower plate. The top plate is then added and riveted in place by hollow brass rivets.

On the 5-Pin Holders you can see a pair of these small rivets at the 10 and 4 o’clock positions near the rim of the Holders. The Pin Terminals on these 5-Pin Holders are thin enough metal they lay quite flat against the top face of the lower phenolic plate when fitted in place. The top phenolic plate helps hold the Pin Terminals in place and also likely stiffens the overall Holder. When you look at the edge shot of the Holders you will see very little gapping between the two phenolic plates. Not so with the 7-Pin Holders.

The Pin Terminals for the 7-Pin Holders are quite robust by comparison to the ones on the 5-Pin Holder and they do not lay flat against the top of the lower phenolic plate at all. A large tubular brass rivet is used at the centre of the 7-Pin Holders to secure the top phenolic plate in place. This leaves a noticeable gap between the two plates, which if not resolved, would likely warp the Holders when riveted to the chassis causing long term problems.

To solve this problem, small phenolic washer-like spacers were inserted between the two phenolic plates to take up the gap where the mounting rivets were placed. During the manufacture of these Holders, these spacers were very likely lacquered in place to secure them, but after 80 years, the adhesive quality of the lacquer has failed completely. As I happily popped the first set of these holders off the receiver chassis, I was surprised to find several of these spacers on the workbench, along with a lot of fine yellow dust. Fortunately, all spacers were accounted for in the end.

The assembly station on the line where these Holders were fitted is another one I would like to have seen in action.


David