[Milsurplus] A relay transient suppression circuit.....?

[Hubert Miller]

Going thru some manuals today, deciding which to keep and so on, i find one
for a keying 'control panel' by RCA. It says this: 

"Each relay has an RC circuit in series with a diode across the coil to
provide transient suppression. This RC circuit lowers the maximum keying

rate to about 80 WPM based on a standard word equal to 25 centerholes of
Morse tape."  

 

The relays are provided with a -12 dc. The relay coil has connected to this
hot -12 end, a diode 1N459 anode ( reverse biased ); the diode

other end ( cathode ) goes to a paralleled 10kR and 2.2 uF connected reverse
to the operating voltage across the relay. Is that RC to 

prevent damage to the diode by the reverse EMF of the coil, on break
(opening ) the relay circuit ( by ungrounding the cold +12 end of the

coil, where a hand key or auto keyer is connected ? And probably the delay
effected by the capacitor discharging slows the coil release? 

Why the capacitor at all? The diode and resistor should do the job, i would
think, and the inrush current into the charging capacitor ( by

the reverse coil EMF ) i would think, puts a big initial current spike thru
the diode? 

What think?

thanks-

Hue Miller 

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