Mauro wrote:

Typo error: T-4X and T-4XC.
Mauro

The T-4X was the original transmitter of the 4-line that came out in 1964.
The T-4XC came out 10 years later in about 1974 and had some solid-state
circuitry.
They are the same basic block diagram but the circuitry is considerably
different.

-Bill