As I was rummaging through some of my stuff this evening I came across this old General Electric Photo Electric Relay that was given to me 60 years ago.

 

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I wondered if it still worked so I hooked it up. It did not work so I began to trouble shoot it for the problem. As I worked on it I was remembering the man who gave it to me. His name was Wilfred Klatt and he worked in some capacity with the local power supply company. At that time it was called NSP or Northern States Power Co. I do not know what Mr. Klatt's job at the power company was but as a close friend of my parents he became the go to guy when they wanted to check out the safety of one of my inventions, prior to letting me plug them into the wall. Mr. Klatt or Willie as everyone called him never hesitated to try to help me out with my electrical questions. When he would find an interesting piece of equipment that was no longer in service and about to be thrown out he would save it for me. This photo electric relay was one of those things. Those of you who are currently inspiring or mentoring a young person, who has an interest in electronics, should take note. Willie Klatt made a contribution to my interest in electronics and as such I am still grateful to him all these years later. Perhaps the person you are inspiring will remember you 60 years from now too.

 

The unit is built around a tube 117P7GT which has two sections one of which is a half wave rectifier and the other a Beam Power section. The photo sensor is a 930 photo tube which has a metal screen that is susceptible to loosing electrons when struck by light and an electrode to collect those electrons. Just as is the case with our more modern sensors the more light that strikes the screen the lower the resistance in the tube. The 117P7GT drivess a SPDT Relay made by C. P. Clare & Co. of Chicago. The label says that the coil has 5000 Ohms and has 37000 turns. I don't remember seeing any recent relays where they tell you how many windings are involved in the coil. Here is a picture of the unit from above.

 

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By now I had a pretty good idea where the problem with the unit was. I could see that the dual 20 uF capacitor, the silver cylinder, had leaked over the years and was no longer a capacitor. I found a couple of 20 uF 250 volt axials and patched them into the circuit using the terminals of the old capacitor as a terminal strip. You can see how I have placed the new capacitors in the following picture.

 

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Check out the one and five watt carbon resistors as well as the old paper foil .02 uF capacitor. Incidentally this capacitor still tested out OK though quite a bit higher than its nominal rating. Here are a couple more pictures.

 

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The dial on the front of the unit is not for sensitivity as I initially thought but rather a delay on the release of the relay. The unit is quite sensitive to light as I had to go to near darkness to get it to open the relay and then it would close the relay with only the light of a small flashlight from a couple feet away. I can't think of a safe way to use this unit any longer but I will keep it around as it reminds me of Willie and the help he gave me when my electronics interest was new.