Collins Aerospace Museum

Sep-3 ···
233D Transmitter Restoration Project

Came in late today, so might have missed if anyone dropped by; Mike had other business today, so he didn’t expect to be there.

Pulled the terminal board with all the resistors on the 175R-3 Tone Control chassis to see if there any additional resistors mounted on the bottom. There are 15 resistors mounted on the board and all but two appear to be close to the parts list values. One has been jumpered and I can’t really see enough of the color code to determine what the resistance was. One 510K has been paralleled by a newer 1 meg ohm resistor and a 1K and a 250 ohm have apparently been replaced by small wirewounds.

One thing we need to keep in mind is that the 175R-3 was apparently used for both CW and Phone and had separate local Autotune dials. On our version, it appears that the CW parts have all been removed and a fiberboard cover placed over the chassis. The schematic that we have appears to reflect what we have, while the parts list shows the additional parts used for CW. Looking at the bottom of the chassis shows evidence of hardware (such as external tooth locks) so apparently the chassis was changed at some point to remove the CW parts.

There several obvious mods on the 175R-3 chassis that Mike is chasing. A fairly large wirewound is hanging on one of the connector pins but the other end is not attached to anything. Another wire has been taped, so it was apparently removed at some point. There is a newer appearing yellow wiring that appears so be in the carrier control circuit so that is probably important to chasing our problem.

Kelly started looking at depicting the system wiring so we can hopefully get a better understanding of how the transmitter was supposed to work or why it isn’t.

We made contact this week with an elderly gentleman in Minnesota who worked as radio man for Western between 1940 and 1955. He helped 233D transmitters at Great Falls and Salt Lake City and thought Western may have had others at Las Vegas and Los Angeles. There were 250 watt transmitters “in between” the 3 KW units. We’ll ask him, but his daughter handles his email, so things slow down somewhat. He is about 97, but is reported to be sharp so he can likely fill in more details.