HISTORY:
If you just love 'old' switches (that work) then this one is a beauty!
I have just had some great German equipment from the 1950's 'under the knife' on the workbench and extracted parts of interest, this rotary switch was one of them (I have another multi-pole version too ... it is coming!)
Why all the fuss over a 70 year old switch (I hear you asking while standing on one leg, one arm in the air and one eye closed) ...
It's all about the engineering, solid as a rock and reliability.
This switch is typical of German engineering standards, solid metal used for all switch bodywork and it can be relatively easily dismantled for cleaning or adding further poles.
The top section is all metal and provides the 'click-stop' of each switch position - 7 of them.
The switch wafer below this is the switch itself, easy to 'soak clean' or to just give a squirt of cleaner.
Right at the base of the switch is another wafer which has no switching purposes at all - the idea was that passive components can run between the switch contacts and this bottom wafer, remember this was the days of 'point-to-point' hard wiring, tag strips etc ... no PCB's here!
To a certain extent you can also customise your rotary switch (if you have the centre key hardware in particular), overall this switch has been designed with flexibility in mind.
Notice that this switch is branded ITT, an American company which had considerable commercial interests in Germany before, during and after WWII
ITT - Rotary Switch
Made in Germany
Both ITT and Made in Germany are stamped into the top section of the switch
Circa 1950's
Type: 7 position
Action: 1 pole x 7 position
NOTE: I have not investigated this but it MAY be possible to adjust the stop positions so you could change this to a 3,4,5,6 position switch
Solder tags on the underside of the phenolic resin switch wafer
Hollow solder tags on the lower interconnect phenolic resin wafer, so that component leads can be fed from one side and hard wiring to the rest of the circuit on the other
Switch shaft is 5.9mm round x 11mm length with no flat spot, best to use a collet knob with this rather short shaft (it has not been cut, this was the original size)
I have taken a few photographs with the switch in various stages of disassembly, so that you get an idea of how this switch is constructed.
DIMENSIONS:
Total switch length: 75mm
Switch width: 40mm x 28mm (oval shape frame)
TESTING/OBSERVATIONS:
I looked VERY closely at the switch action between contacts and although there is a definite break-before-make action, I suspect that there is an extremely short period where the 'break' has not yet occurred so in effect two positions are connected together, if only for an extremely brief moment.
I like the switch action very much, extremely positive and the wiper that runs across each of the seven contacts is spring loaded so that constant downwards pressure is applied. At every position contact point I measure much less than 1 Ohm - my present test gear will not reliably give me sub-one Ohm readings.
I also noticed the position contact pad area is quite large, providing a large surface area for the contacts. The base metal looks to be Copper but I suspect there is also a topside plating of either Silver or Gold, most likely the latter as I can see no signs of oxidisation to the contact surface.
I would say that such a large contact area was used because we are talking of the days when voltages were 'real' voltages (up to 600V) and currents were measured in the hundreds of milliamps, not contemporary microamp currents.
The original equipment this switch was removed from was of course all valves...semiconductors were only just emerging from the Bell Laboratories at this time
COSMETIC CONDITION:
USED
CLEAN body
CLEAN switch wiper and contacts
All tags have had most of the previous solder removed, ready to rewire!
Now that the photograph sessions are finished and the description has been completed, I have now placed this "Grandaddy" of switches into a sealed clear plastic packet to maintain the current condition.
