Collins Aerospace Museum

233D Transmitter Restoration Project

Mike is getting the mods to the tone control assembly documented so we can understand how the carrier control system works.

Jules is working through the Autotune sequence to determine why we aren’t driving the motor properly. I have attempted to adapt the sequence diagram from the 231D-13 system to help us understand how the Telco relay assembly translates dial pulses to channel select data.

Next step is to force the exciter to a channel selection capable of tuning to 40 meters and attempting to get some RF out of the 813s. Indications are that the Autotune system was not operational when the transmitter was last used.

One of the drawings had a note about a transmitter at “EJ”. One of the Western Airlines destinations was Calgary. There are a number of Alberta airports with IDs such as CEJ2 or CEJ6. So it is possible that another 233D was installed in Canada. There could have been at least 6 233D transmitters used by Western.

The 233D photo list have numbers in the mid 7000s. The 1943 TDH-2 manual have photo numbers in the mid 8000s. The 231D-13 manual shows photos in the upper 8000s. That would appear to put the 233D sometime before 1943. The TDH-2 manual has a schematic with a reference to the 231D-11. Hopefully, all this will help establish additional detail about our transmitter.

I am preparing a detailed letter to send to the Western Airlines radio man who worked on the 233Ds at Great Falls and Salt Lake City to see if he can add more about the transmitters.