2XX Transmitter Spring Insulators

[dencins]

I was at a local Home Depot tonight and noticed they have changed to TE Connectivity (Tyco Electronics) heat shrink tubing.  I use the black, 1/4" to 1/8" size tubes for the insulators on the ends of the flat springs that hold down the diaphragm on the 2XX type transmitter.  These come 5 tubes of the same size in a package for $2.00.  The old supplier only had the 1/4" size in a package of mixed sizes so the most got thrown away or lost.

The process is simple.  Clean the spring, cut a 3/4" piece of tubing and slide it on the spring up to the bend then heat with a heat gun.  I squeeze the end while it is still hot to get a good flat end then trim.  Each tube is 3" long so one package will do 10 transmitters.

Dennis Hallworth

[wds]

that's a great idea for those springs.  What do you use for the felt underneath the spring?

[dencins]

I have not been replacing the felt - only the insulator.

I ran tests a few years ago with and without felt and did not find any difference that I could recognize.  I tried a few different materials but all results were the same.  One material I used is called moleskin that I got at CVS.  It is a tan cotton flannel with an adhesive back.  I cut a 3/8" x 3/8" square and stuck it on.  It looks much like the original material.

Insulating the faceplate from the diaphragm must be done or the transmitter will not work correctly.  The screws to hold the springs go into the faceplate so the spring needs to be insulated from the diaphragm.

I could not find any functional reason for the felt.  My other thought is the felt provides an extra layer of insulation on the spring if the rubber insulator fails.  Possibly the engineers knew the rubber would deterioate and eventually fail.  These transmitters were pre-1900 and the felt was an inexpensive extra assurance to gain longer useful life.

Dennis Hallworth   

 

[HarrySmith]

Just received a message on the lists from Steve Hilsz about these, I don't think he would mind so I am reposting it here:

 
In case you break a transmitter damping spring (the one that is fastened to the edge of the transmitter and pushes against the diaphragm, I have some new-old-stock universal replacement springs available. They are cut so they can face either way on the ridge, and they come with a rubber insulator and a little felt pad. These were manufactured in the 1930's and came from an old Independent telephone company's shop. I got them from Oral P. Watts when he still had The Old Telephone Exchange in Coffeyville, Kansas.

The springs are $1.00 per set plus postage.

Steve Hilsz
jydsk@tds.net