Vintage diodes: what semiconductor?

Thread Starter

Alec_t

Joined Sep 17, 2013
12,206
The other day I dismantled an analogue multimeter, which I had built from a kit in the early sixties, and found these two diode half-bridges.

Bridge.png

I'm wondering if they could be WW2 surplus?
Each diode reads about 1700 (when forward-biased) on the diode-test setting of my DMM. I'm guessing the half-bridge is constructed by centre-tapping a selenium-coated strip/rod. Thoughts?
 
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Thread Starter

Alec_t

Joined Sep 17, 2013
12,206
Thanks for the link. So it was made by Westinghouse, but I'm still curious as to the semiconductor material and history.
Incidentally, that Radiomuseum entry describes it as 'full wave', but you'd need two of them strapped together to make a full-wave bridge.
 
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Thread Starter

Alec_t

Joined Sep 17, 2013
12,206
But it can still be a single-device full-wave rectifier:
I don't see how. The two internal diodes are connected in series, anode to cathode (not cathode to cathode as shown in post #4).
Someone (the kit supplier?) has obligingly marked the device with + ~ -.

Edit: Ah. Now I see how. I've just come across this Westinghouse booklet, dated 1937, in which Fig 2 shows a voltage doubler rectifying arrangement. A price list at the end interestingly lists W.M.24 and W.M.26 type rectifiers as 'Full wave centre tapped'. So my curiosity is now satisfied. :)
 
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Thread Starter

Alec_t

Joined Sep 17, 2013
12,206
Ah yes, the smell. I remember cutting up a selenium rectifier plate many moons ago and can still conjure up that aroma.
When disassembling that old multimeter I found inside it the BOM and kit price: £3 9s 11d. About the same (discounting inflation) as today's price for an el cheapo DMM! Just shows how mass production has brought down the price of electronic goods drastically, in relative terms, over the intervening 50 odd years.
 
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