My XD Keyer is about 2 months old. It has the PS2501-2 opto isolator
in the PTT circuits.
The opto diode series resistor is 1.2K in the Keyer. I paralled a 330
ohm with the existing 1.2K's, and the PTT now works on both my TS-850's.
The spec sheet says absolute max diode current is 80 Ma, so it looks
like 20Ma or so is safe, and drives the switch hard enough now.
Dennis K5YA
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