Re-installing a TouchTone keypad in an ASR-33
mcguire at neurotica.com
Mon May 18 15:17:48 CDT 2009
On May 18, 2009, at 1:32 PM, Chuck Guzis wrote:
>> I'm not a telephony geek, but this comment prompted me to go look
>> at that schematic. That's a really neat little circuit. What are
>> the four odd components? The symbols sorta look like DIACs.
> Varistors. Telco stuff was usually silicon-carbide rather than metal
> oxide. Although they were used for circuit protection, and amplitude-
> limiting (look inside the receiver of any 2500 series desk set), they
> were also used for circuit stabilization, which is, I think, the
> application in the dial circuit.
Oh, how thoroughly bizarre. Thanks for the explanation. I'd love
to see a SPICE simulation of that.
Port Charlotte, FL
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