Question about analog voltmeters and antique telephones
Question about analog voltmeters and antique telephones
I recently started setting up an intercom system between my workshop and the kitchen using a pair of antique Leich 901 telephones.
These are old local battery, crank/magneto phones originally intended to be used on small co-op networks (sometimes run over barbed wire!) or other odd uses. Each one has a crank which generates AC to ring all the phones on the circuit, and a talk battery (usually in a separate case) to power it as it was assumed houses didn't have electricity.
I've been able to get them talking following these guides:
https://www.valhallatreefarm.com/magneto%20phone/phonemagneto.htm
Now I'm planning my next steps, which include setting up a nice display panel for the workshop phone (partly to make hanging it on the wall a bit easier).
One of the things I'm thinking of is adding a small voltmeter to the voice line, like in this picture:
From their description of "When you speak, the needle moves rapidly like a VU meter!" I was assuming it's a 0-5 Voltmeter (maybe something like this) but Im worried about the AC ringer power coming down the same line.
According to the best guide I've found: "It should put out about 75 Volts AC when vigorously cranked." While the talk battery is only 4.5 Volts DC.
I have some huge holes in my understanding of electricity (especially considering how often I mess with it) but I'm worried an analog 5v Voltmeter wouldn't like 75 volts. I've read Voltmeters are supposed to be higher resistance than the circuit they're measuring. Does that protect it in a situation like this? Otherwise is there a way to safely set this up? Bonus points: is there a way to rig a light that blinks or flickers using this circuit in case I can't hear the ringer over tool noise and earpro?
Thank you very much!