Well I have found another receiver this past week that will be serving as a parts doner for my Main Set and Remote Receivers. It is complete but has been in a humid location somewhere just long enough to build a bit more surface rust on the chassis than is worth dealing with. Also, a number of key decals on the front have been badly damaged/chipped away. Not a choice I take lightly, but other events this week led me to conclude it was a wise decision.
I started to clean and visually check the valves on the Remote Receiver, starting with V2B, the 12Y4G Noise Limiter. I chose that one as it was missing it's shield cap and I now had a replacement from the doner receiver. You can see this valve in Post 37, horizontally mounted, mid rear chassis.
First thing I discovered was this valve is the only receiver valve that does not have any physical locking means to keep its shield assembly in place. Consequently, Marconi sweat soldered the base of the shield to the valve socket and coated the solder seam with clear red lacquer. Marconi appears to have used this lacquered solder technique throughout the 52-Set Receiver chassis. This valve is the most difficult to get at on the chassis and it takes a bit of wiggle to remove it from the shield. When it was out, I realized the top of this particular shield was different from others I have encountered. The top edge is straight cut, not rolled in, The rolled in approach makes for a very firm shield top that a cap can be pushed over very easily. Not so the straight cut edge as a close look showed several dents and bumps around it. Which explained why the cap was missing. Back to Debbie's jewellery supplies for her small, smooth faced, needle nose pliers. After nearly 45 minutes of bending, tweaking and muttering, I finally had the edge of the shield smooth enough to accept the cap. Then the second problem smiled at me.
The 12Y4G has no central key post on its base. It relies on proper seating in the socket by the pattern of spacings of the pins, No big deal for a vertical installation with no shield to deal with. Very big deal in a horizontal mount with a fixed shield obscuring any observation of the process. I ended up staring at the bottom of the socket at the back of the chassis, with a flashlight in one hand while the other twiddles the valve, which I hoped was at least starting out in somewhat correct orientation. Only took 10 minutes.
Extra valves on hand are going to be a definite asset with this project!
David
|