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Old 15th Aug 2018, 9:13 pm   #7
Dave Moll
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Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,130
Default Re: Payphone 500 / 600 handsets

Quote:
Originally Posted by OscarFoxtrot View Post
There are no transistors or anything else active in the 2/3T so it can't be needing a DC bias voltage.
The only other reason for needing a DC voltage there that I can think of is to energise a field coil if a receiver uses one of these instead of a permanent magnet.
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