[GreenKeys] Using Lenkurt 25A as loop supply

[Charles Ring]

Mine is the same as yours, 25A, but marked UPI. I had not noticed the A 
or B. The plugin sealed demodulator modules are missing from both of 
mine. Most likely I thought them useless and removed them. I saved the 
25A's for use as loop supplies. The loop appears at terminals 4 and 5. 
and grounding 6 to 3 makes it act as a constant loop supply. UPI used 
them that way  after going from phone line to satellite feed. Terminals 
1 and 2 are for the incoming multiplex audio via a copper loop from a 
central office. The 25A picks out one signal and decodes it. One of mine 
has a label with spaces for Channel, Frequency, and Circuit, but the 
figures for those are too faded to read.

You don't need a series resistor when using this as a loop supply. It 
puts out 150VDC with internal current limiting. Set it to 60mA with the 
front panel loop current pot.I don't know if it can be reduced to 20mA 
and work right.


73 de W3NU