Transmitter Capsule Disassembly and Refilling

[Matilo Telephones]

Busses, eh? Perhaps I can strike a deal with a traindriver on one of the trains that pass near my house. 

[Phonesrfun]

I once bought an 11-digit Strowger wall phone, and when I got it, the solid back transmitter would not work and tested open with the ohm meter.  I opened the carbon button only to find that someone had been there before and emptied out all the carbon.


I took a couple T1's and opened them up and tapped out all the carbon onto a folded piece of paper.  Then I carefully held the fold of the paper over the hole of the AE transmitter and filled it to where I thought the "full" point was.  Purely a guess.  I put the plug back in and Viola!  it worked.  Fortunately, it does not have the crimped cap that a T1 or F1 has.  The Strowger just sits on the wall, but if I ever want the voice circuit to work, at least I know I have a working transmitter in it.

[Bill]

Hey another thought. Get one of those old electric/vibrating football games, lay your broken/weak capsules on the playing field, flip the switch, presto, instant shake-up

https://www.youtube.com/watch?v=vgFZIS_a3CE

Old thread, I know. But the above might not be such a bad idea. How about getting an old electric doorbell with the exposed gong(s), remove one gong, attach the capsule in its place (duct tape?), and let the clapper tap on the edge of the capsule for a while. Rotate occasionally if needed. It should break up the carbon quite nicely, without spending hours manually tapping it on a table, beating it with a screwdriver handle, or denting the capsule.

Bill

[Scotophor]

Bill, this is a telephone forum! No doorbells allowed ... what is needed is a circuit to continuously ring a telephone ringer, and a sturdy transmitter element holder fabricated to replace one of the gongs. The other gong would of course be removed for sanity's sake. I think a 60 Hz frequency ringer would be ideal for the purpose, since it could simply be connected directly to a standard wall outlet (at least here in 120-volt land). If the element holder were mounted slightly off-line from the clapper and allowed to rotate freely, the clapper impacts would make it spin so that the element would be tapped from 360 degrees. It would probably only take a few seconds of such treatment to renew most transmitters, as long as the carbon hasn't been contaminated by something sticky (or removed entirely ).

[Charles]

I recently found an electret mic replacement for the T1 carbon transmitter. It is the same shape and size as a T1 so it drops right into a G handset and is powered by the phone. The transmitter sounds better than a new carbon T1.

Here is the link on ebay:
http://www.ebay.com/itm/Phone-Transmitter-OZ-01-Electronic-Telephone-Transmitter-for-Handset/181795652144

?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

[Dan/Panther]

If you use a ziplock bag, you should evacuate the the air inside the bag. A straw, with the bag closed up to the straw, draw out the air, as you slip the straw out of the bag, and at the same time seal the bag.
A ziplock bag with air inside will act like a cushion against the ultrasonic waves.

D/P

[Alex G. Bell]

Varistor = Variable resistor, it changes it's resistance as it warms up, therefore directing unwanted current away from something that is sensitive to current...

http://en.wikipedia.org/wiki/Varistor

Wikipedia or not, a varistor responds to voltage, not temperature.  A thermistor responds to temperature.

[Alex G. Bell]

If you use a ziplock bag, you should evacuate the the air inside the bag. A straw, with the bag closed up to the straw, draw out the air, as you slip the straw out of the bag, and at the same time seal the bag.
A ziplock bag with air inside will act like a cushion against the ultrasonic waves.

D/P

I don't understand what previous message this applies to or what the context is.

[Alex G. Bell]

I recently found an electret mic replacement for the T1 carbon transmitter. It is the same shape and size as a T1 so it drops right into a G handset and is powered by the phone. The transmitter sounds better than a new carbon T1.

Here is the link on ebay:
http://www.ebay.com/itm/Phone-Transmitter-OZ-01-Electronic-Telephone-Transmitter-for-Handset/181795652144

?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

I wonder whether this is really electret as the seller states.  Carbon transmitters require a large diaphragm clamped tightly, hence a metal body like this.  Electrets only need a 1/8" pin hole and can be molded from plastic much more economically.

A test for which it really is would be to check its resistance change with applied voltage.  At 1V or less a carbon would read about 50-100 ohms while an electret most likely would be an open circuit.

[Charles]

There is no carbon inside (shaking provides no sounds). It appears to be mostly hollow. There a small device mounted in the middle covered with a thin plastic sheet (I guess to keep out moisture). Whatever technology it is using is very loud and clear.

[unbeldi]

Varistor = Variable resistor, it changes it's resistance as it warms up, therefore directing unwanted current away from something that is sensitive to current...

http://en.wikipedia.org/wiki/Varistor

This is not the claim by the Wikipedia article at all.   A varistor has an intrinsic non-linear voltage-dependency of the resistance that has nothing to do with temperature.

Also, the description varying resistor is more accurate. Variable implies some external control as in a potentiometer.

[dsk]

Do you have a procedure for testing old carbon transmitters? I have so far just putted them in vice and tried to deem the quality to talk and listen.

dsk

[countryman]

I have built a little test stand on a piece of plywood when I played with microphones. First I hooked them directly to the mic input of the phone laptop but the current offered is very small compared to a telephone circuit. It works on some transmitter capsules, though.
The test stand uses a 9 Volt battery and a 680 Ohm resistor to power up the capsule. The capsule either is pinched between the contact tongues or it is connected with the test clips. The small capacitor (brown disc) couples the signal to the mic input of my laptop. Then I recorded my voice using this site: https://online-voice-recorder.com/de/
That went well - too well in fact, as most any weak capsule tested much better than in actual telephony, while good working ones sometimes delivered only mediocre results.
Interesting, but I gave up the project.

edited to correct error

[dsk]

Good Idea, but as you mentioned not good enough, I had an idea of sending out a sound signal of 1 kHz and analyze what the transmitter sends, but only one frequency may also be to narrow.  Maybe just testing and listening might be good enough :-)
dsk

[Sargeguy]

Give it a few hard raps and put it in an empty rock tumbler overnight, that will toss it around and should loosen things up.