Chassis – Mount Tube Sockets / Variable Caps


Yesterday the mounting hardware arrived.  I had ordered a number of different length 6-32 zinc-plated machine screws ranging from 3/16 in. up to 5/8 in. from McMaster Carr.   While BoltDepot was cheaper for the same machine screws, McMaster had narrow 6-32 zinc-plated nuts and 6-32 Black-Oxide truss head machine screws (for the front panel) that BoltDepot did not carry.   The narrow nuts (1/4 in O.D.) work better for mounting certain parts than standard 5/16 in. O.D. nuts.  After factoring in shipping, it was more economical to just get everything from McMaster.


The tube sockets were mounted using 1/2 in. 6-32 screws, #6 external tooth washers, flat washers, and standard 5/16 in. O.D. nuts.  The National SW-3 has it’s tube sockets mounted with some space between the socket and the chassis, but I decided to flush mount the sockets for more rigidity.  Due to the way the ceramic sockets are constructed, there are rivets exposed at the top of the socket holding the contact fingers in place on the bottom.  Since they are electrically connected to the socket contacts, there needs to be adequate clearance from the lip of the mounting hole.  The 1-1/2 in. holes in the chassis provide enough clearance so it is not a concern.

The two(2) ST-75 (75pF / 180 deg; RF amp and 1st Detector) and one (1) SE-50 (50pF / 270 deg; HFO tuning) variable capacitors are mounted using 3/16 in. screws and an external tooth washer.

It’s starting to look like a radio chassis now…..