[GreenKeys] Relays for the Loop? It can be done!

[Charles Days]

Joe,


Yes, the 255 polar relay will work.


For rec/transmit, two polar relays are required and a third relay (not polar and does NOT key at 60wpm) used to short the sets of contacts so the loop can both receive and transmit depending on this "T/R" relay.


The polar relay(s) required 30 ma., current can come from the REC-30 supply and it is used for one winding in each polar relay It is the "spring" for the relay. The two "spring" coils in the relays can be in series, they will have a constant current set by a series resistor.


The transmit polar relay will have its other coil in series with the loop and in series with contacts of the receive polar relay.


The T/R relay can be a plate circuit type, it too, can be powered by the REC-30 supply if need be.


NO damping diodes are used, no capacitors, any such modern crap will cause distortion of the TTY characters. Nothing across the coils as that will effect the rise/fall time of the TTY characters, distortion.


I built such a unit AND built it for two lines that the 19 set has, therefore four polar relays.


This setup is all neutral keying but no reference to the frame of the machine, all above ground.


I have several old T/U's that are ground reference and a polar keyed exciter. So this TTY interface solved the problem and allows me to keep the 19 exactly as it was intended. One exception there is a LARGE Jones plug in the rear. This is where I terminated all the lines and provide DC from the REC-30 to this interface via a cable He, he, shielded with electricians Greenfield, that's all I had. Good choice, I can roll around the 19, the casters would crush an ordinary cable, not the Greenfield...


I have no problem with 255 polar relays. I have collected them for years when they were cheap. What was hard to find are the sockets.


Anyone remember John Mesha, Allerton St., Lynn MA? That is where I got a polar relay test set and a pair of master calibrated relays. The test set operates off of one of the DC plugs in the 19 supplied by the REC-30.


Not all polar relays will calibrate, if the magnet is too dead, the magnet will have to be recharged or replaced. Some magnets will not recharge :(  The stronger the magnet the more sensitive the relay the less loss of signal pulse width, reduced distortion...


BTW very early polar relays used a metal cover, later a molded Bakelite cover. I used metal covers on all my relays and grounded the cover via the perimeter plugs on the relay. I used this setup on 6 meters, I had no RFI interference in the receiver.


Once a relay has had a "golden screwdriver" in it, no bench work can put it right without using a test set.


When correct, the relay operates as a mechanical filter too, they won't key to static pulses.


If one intends to use polar relays I may be able to calibrated and verify their sensitivity of their relays at some time in the future...


Looking to swap those services for someone to build or supply a reperforator table from steel or fine hardwood construction. Steel, black wrinkle preferred, I will pay shipping...


He, he I rigged the manual transmit key on the front of the 19 to key the transmitter via that T/R relay in that polar relay interface.


As always YMMV.


If too complex, use optocouplers :|


Chas


WA1JFD




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