Guildline low thermal selector switch teardown

[doktor pyta]

Guildline low thermal selector switch model 9145A10.
The position (0 or 90 degrees) of switch marked with two dots determines if the whole set is locking or momentary.
Some old papers found in google books claim this model is specified as +/-10nV thermal EMF. Nice.
Have a tea and watch

[doktor pyta]

2

[doktor pyta]

part 3

[TiN]

Thank you. Interesting design with silver (?) bars. Copper lugs to equalize temperature, while silver pad to provide low resistance contact? 

[RobK_NL]

Heh, I've got its little brother here; the 5-channel 9145A.

Thank you. Interesting design with silver (?) bars. Copper lugs to equalize temperature, while silver pad to provide low resistance contact? 

Yes, those contacts are silver. But I've always wondered about the design, especially concerning the "low resistance" part.

Those silver bars are almost 10mm long, but the bars on the plungers are round, so the actual contact area is only a few 10ths of a mm.

[doktor pyta]

I may be wrong but it does not look like pure silver, rather some harder alloy. The shorting rods are mounted on flat springs so the contat is self-cleaning.

[manganin]

Some old papers found in google books claim this model is specified as +/-10nV thermal EMF.

As far as I remember, repeatability of something like a few hundred nanovolts can be achieved. But soon you will have a nanovoltmeter to do the tests...

Rather than low thermal I would call these high reliability switches. In addition to the contact pressure the spring also produces small wiping action cleaning the silver alloy oxidation.

Very long life, even when operated by solenoids.