SC transmitter repair or replacement

[cloyd]

Hi!

I am working on making repairs on the SC 1212 fatboy that I bought at a low price on ebay.  So far, I have $100 into it for the phone, gasket, AE type 24 dial, ringer (64C-247) and now I may need a replacement transmitter.  Ugh.

Since it wasn't transmitting any sound at all, I went ahead and took it apart out of curiosity.  I glued down the material that surrounded the metal cone and reassembled it.  It works much better now but still not well enough.  I really wasn't expecting my efforts to make any difference so I was pleasantly surpriced.  Is there anything else that I might try to improve the volume?  I lost a small amount of the carbon granules.  Might that explain it?

If anyone has a spare transmitter #205784: the number on my transmitter or #24562 the catalog part number for the curved handset #15, lets talk.

Thank you,

Tina

[Dan/Panther]

I think I would look for a replacement, but if you decide to repair it, the carbon particles are critical, do you have all of it ? The particles vibrating against each other is what transfer the sound.
A few years back I made a meter device to test the elements for functionality.
Basically the way it works.
You place the element face down over the rubber ring, you place the contacts onto the rings on the back of the element.  Inside the rubber ring is a small microphone. Set the pot to 0, then click the switch, Increase the pot until the feedback stops. The higher the reading the stronger the element.  Many times just a good rap on a hard surface brings a non working element back. The carbon sticks together and won't create any current through vibration.

D/P

[TelePlay]

Dan/Panther,

Did you post the wiring diagram and parts list for this tester anywhere on the forum?

Looks like a simple device I could use.

[Dan/Panther]

I don't think I did. I can pull it apart and make one up.
I built it about 6 or 7 years ago.

D/P

[unbeldi]

Dan, I don't understand how this device works.

How do you create feedback when you have a transmitter and a microphone (=another transmitter) facing each other?
Do you mean the device has a receiver or speaker ?   A speaker/receiver element would emit a tone and the testing object would register a signal. That seems to be the only way I can imagine to get "feedback".

[Dan/Panther]

The speaker in the round tube sends a signal to the receiver/transmitter sitting above it. If the element is working feedback occurs. It's like hooking a speaker to a 9 volt battery, you get a pop  or crackle, my contraption just feeds that pop back into the system to repeat itself.
I can't explain how or why it works, I get these hairbrained ideas, I trey them, and they work after some tweeking. The weird thing is after a few years I look at things and even I get surprised at HOW did I do that, I just forget.

D/P

[unbeldi]

Thanks, Dan.
I just wanted to get confirmation that in fact you have a speaker in the box, not a microphone as reported originally, see insert.

The feedback generated by the combination of a speaker and the transmitter to be tested is the same kind of feedback one gets when calling from one telephone to another that is just a feet or two away.  It is the same kind of feedback that haunted and delayed the satisfactory introduction of the single-unit handset with transmitter and receiver built-in in the Bell System.  The early E1 handsets (A,B,C, and D-handset) suffered from this kind of howling, which came from the acoustic coupling of receiver and transmitter through the handset handle.

The oscillations are triggered by any kind of sufficient sound impulse in the transmitter. The transmitter amplifies it by the nature of its operation, and sends it via the circuit to the receiver, the receiver plays it out and the transmitter receives it and amplifies it even more, and so the cycle continues with increasing volume until saturation.

Indeed, the better the quality of the transmitter, the better the feedback circuit works.

I think I would look for a replacement, but if you decide to repair it, the carbon particles are critical, do you have all of it ? The particles vibrating against each other is what transfer the sound.
A few years back I made a meter device to test the elements for functionality.
Basically the way it works.
You place the element face down over the rubber ring, you place the contacts onto the rings on the back of the element.  Inside the rubber ring is a small microphone. Set the pot to 0, then click the switch, Increase the pot until the feedback stops. The higher the reading the stronger the element.  Many times just a good rap on a hard surface brings a non working element back. The carbon sticks together and won't create any current through vibration.

D/P