I have built a 19-station intercom system for my community theatre, and Im having trouble with the circuit.
I used an Elgin EAK-4 key, coupled with a Tel-Tone T-19 switcher. I managed to locate the original T19 wiring guide and followed it explicitly. THis routes through a series of Western Electric 2500 touch-tone telephones. The EAk-4 and the T-19 were given to me free of charge. The phones were procured from a thrift store. The circuit is encased in a plywood box with a 3" exhaust fan.
On intial testing, the system appears to operate perfectly - all phones can talk back and forth on signal and each unit can "ring" any other unit in the system. However, once all units are connected, some cannot send or receive rings. So far, in all tests, there is a time difference of 30 minutes to an hour between first test (two units) and final test (10 units).
I was getting frustrated with this symptom when it occured to me that I have a second that I had heretofore ignored: after 1/2 hour or so, the signal volume on all units drops to a point such that the voice on the other end of the line is barely audible. It belatedly occured to me that both symptoms could easily share a single cause - voltage drop.
My first thought was a heat related problem, so I removed the cover from the box, turn the unit off, and waited 1/2 hour. No better. Next, I considered the ground; all grounds are made to the chassis of the EAK-4 using 20-gauge wire. So, I used a 12 gauge cheater to ground the circuit to a 4'x4'x9" steel junction box on the wall. Again, no improvement.
Now, I'm thinking there are two remaining possibilities - (1) I've screwed up something in the 124 connections used in building this circuit, or (2) there was a really good reason why these parts were free.
Thoughts?
I used an Elgin EAK-4 key, coupled with a Tel-Tone T-19 switcher. I managed to locate the original T19 wiring guide and followed it explicitly. THis routes through a series of Western Electric 2500 touch-tone telephones. The EAk-4 and the T-19 were given to me free of charge. The phones were procured from a thrift store. The circuit is encased in a plywood box with a 3" exhaust fan.
On intial testing, the system appears to operate perfectly - all phones can talk back and forth on signal and each unit can "ring" any other unit in the system. However, once all units are connected, some cannot send or receive rings. So far, in all tests, there is a time difference of 30 minutes to an hour between first test (two units) and final test (10 units).
I was getting frustrated with this symptom when it occured to me that I have a second that I had heretofore ignored: after 1/2 hour or so, the signal volume on all units drops to a point such that the voice on the other end of the line is barely audible. It belatedly occured to me that both symptoms could easily share a single cause - voltage drop.
My first thought was a heat related problem, so I removed the cover from the box, turn the unit off, and waited 1/2 hour. No better. Next, I considered the ground; all grounds are made to the chassis of the EAK-4 using 20-gauge wire. So, I used a 12 gauge cheater to ground the circuit to a 4'x4'x9" steel junction box on the wall. Again, no improvement.
Now, I'm thinking there are two remaining possibilities - (1) I've screwed up something in the 124 connections used in building this circuit, or (2) there was a really good reason why these parts were free.
Thoughts?
