Comments on: Help identify this mystery component!

By: Kabel

Kabel — Fri, 29 May 2009 08:10:59 +0000

It is, as you guessed:
A back to back diodes that protect the person using the phone from strikes or other high voltage on the line.

By: typ.o

typ.o — Thu, 25 Dec 2008 13:15:45 +0000

In vintage telephone sets in Germany i found a similar thing which is named “ear protection rectifier”, consisting of two antiparallel normal si diodes.

By: Darryl Smith

Darryl Smith — Sun, 21 Dec 2008 23:20:54 +0000

I agree – probably a two anode zener. What this does is to restrict any voltage to 0.6V + the voltage of the individual Zener. And it is non-polarized.

Also common on phones is a Voltage Dependent Resistor. Not sure how they worked, but with pulse dialing they were used to stop other phones in the house ringing.

By: Alex

Alex — Mon, 24 Nov 2008 03:00:51 +0000

Diac or two-anode zener is used to protect speaker from the ring voltage in case you pick up the receiver when phone is ringing.

By: Jeff

Jeff — Thu, 20 Nov 2008 16:12:04 +0000

Ok, so it’s almost certainly a Diac, given the schematic symbol, but what’s it for?

By: Eric

Eric — Thu, 20 Nov 2008 00:03:47 +0000

Welp, that would certainly account for the open you were getting

By: Florin

Florin — Wed, 19 Nov 2008 22:44:03 +0000

As JKirchartz said, it’s a diac, that’s the symbol for a diac

By: JKirchartz

JKirchartz — Wed, 19 Nov 2008 22:37:58 +0000

It’s a diac, check it out @ http://en.wikipedia.org/wiki/Diac …

By: Eric

Eric — Wed, 19 Nov 2008 20:50:29 +0000

An axial capacitor would measure as an open here….Does your DMM have a capacitance meter? I think they use to put 10pF caps across the leads for, as you stated, a filter.

Other than filtering signaling out, it could also be used to keep 60hz buzz under control too.