Re-installing a TouchTone keypad in an ASR-33
cclist at sydex.com
Mon May 18 12:32:29 CDT 2009
On 18 May 2009 at 12:28, Dave McGuire 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.
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