Several have asked about replacing the carbon microphone element  in the T-17. I usually use a standard telephone button and trim it to fit inside the T-17 housing by removing the outer frame. The button then fits inside the T-17 housing and the outer cover  with the small center holes can be fitted. (Drill additional center holes if necessary to improve voice response) Other have taken a T-17 housing and machined the interior  to  enlarge it to accommodate the larger button but removing the outer frame  with a small file is faster and easier.  There is no compassion between the audio output level between the original T-17 cartridge which has aged and the telephone button, the button  is loud and very crisp.
Info on the T-17 including the button mod,capacitor info, rewiring etc can be found at  the link below. In addition there is a chart supplied by WA5CAB on the different  contract dates and manufacturer  of which  I've added a couple of entries. I will add additional info to the chart if I receive the information.
Z
http://k4che.com/T-17/T-17.htm