SC transmitter with weird resistance reading

[RB]

I have a SC 1248wi mod 2
The transmitter gives me a 1.5k ohm reading briefly, then drifts...and sound is very low.
Is this a typical bad transmitter?
What is it supposed to read?
Can I get a replacement/upgrade?
Thanks for any info/help

[Ktownphoneco]

RB  ....    Transmitters are filled with carbon granules.     They are not tightly packed so as to prevent movement.     Resistance readings will, and should, fluctuate continuously if there is any movement of the transmitter housing, no matter how slight.     The fluctuating resistance is caused by a constantly changing path as the current passes through the carbon granules.   If you were to place an ohm meter across the 2 terminals of a transmitter, and obtain a solid consistent reading, then there's something wrong with the transmitter.    The best way that I've found to test a transmitter, is to install it in a telephone and listen to your own voice in the receiver with the set off hook.      There are some scientific ways of testing a transmitter, but it requires some additional equipment to do so.    Transmitter performance can be effected by age, diaphragm condition, moisture inside the transmitter which can cause clumping of the carbon granules, and even loss of carbon over the years, and frayed conductors or anything else that can interfere with the connectivity of the transmitter to the talk circuit.

There are several forum members who can add additional information, and who have expert experience with transmitters, and I'm sure they'd be more than happy to help you as well.

Jeff Lamb 

[HarrySmith]

One thing to try is rapping the unit, as was stated previously the carbon granules can clump up causing poor sound. Just a good rap, flat on a hard surface should suffice to loosen them up.

[RB]

Thanks for the replies, I will try that.