Not a very productive week at all in so far as the 52-Set Project goes. I did get another spreadsheet drawn up for logging the Voltage Values deemed relevant from all the receiver valve by Canadian Marconi Company in the 2nd to 4th Echelon Maintenance Manual, and have now got those values from the Main Set Receiver logged in. Still a lot more of this sort of analysis to finish, however. I did find one interesting thing through all this though.
Another oddity has surfaced related to Valve V2B.
All the valves in the 52-Set Receiver utilized directly heated filaments and this is typically provided directly from the battery voltage used to power the set. In this case, 12 Volts DC. With North American valve production, these filaments, or heaters, are connected to Pins 1 and 2 on the base of the valve. The valve pin numbering system is different in the UK, so going at least as far back as the Wireless Set No. 9 Mk I*, CMC converted the valve pin numbering system used on the British Based Valves to North American standards, to avoid any confusion on the assembly lines. So for all the valves in the 52-Set, then, Pin 1 will be the Plus side of the 12 Volt Heater circuit and Pin 2 would be the return side.
So one of the voltage checks for the 52-Set Receiver is to see that the filament/ heater circuit is working and to do this, you take a reading from Pin 1 to Ground on all of the valve sockets to confirm 12 Volts is present. If you get nothing on your meter, the Pin ! circuit is open and the valve has failed, or the heater circuit ahead of the valve socket you are testing is broken somewhere.
During this test process on the Main Set Receiver, I arrive at Valve V2B and got a reading of ‘0.004’ on my meter. Odd, because I had just tested all the valves a few days ago and this one was working perfectly. Even odder, because I am looking at the valve and can clearly see the heater glowing happily away at the top of it. We can even kick it up another notch! This has been the reading I have been getting from Pin 2 on all the other valves up to this point. So I check Pin 2. I get a meter reading of 12.71 Volts, which is exactly what I have been getting from Pin 1 on all the other valves, and which is a match to the output voltage from my ZE-11 Remote Supply Unit.
When I look at the wiring on the bottom of the V2B valve socket, it is all undisturbed, factory original soldering. Mystery solved. Somebody made a mistake on the assembly line wiring up this particular socket. In fairness, the mistake is no big deal as the Heater Circuit is isolated from all the others in the receiver and the heater will work happily wired either way. What got really interesting, however, was that when I got around to the same testing on the Remote Receiver several days later, the same result was found. At that point, I also decided to check the spare receiver. Same thing. All factory original soldering and all soldered with Pins 1 and 2 flipped.
There is no logical reason for wiring these two pins in this way deliberately, so my suspicion is that this was likely an error in the production line assembly instructions drawn up for the work station involved with wiring in the heater circuit connections for the V2B socket. The error was missed and never found and corrected.
Interesting what one can discover 75 + years after the fact.
David
|