Building trust every day  Rockwell Collins Museum

Jun-17 ···
233D Transmitter Restoration Project

Another great day in the radio room!
Nice group on hand except for Jules who is on injured reserve this week, but expects to be back next Wednesday.

Larry and Mike got the high voltage cabling assembly between the power cart/plate transformer complete and we can now get the high voltage rectifier back and start producing some high voltage when all the components get hooked up.

Rod expects to get the exciter done soon, so we can really get started with the final assembly and get started with testing.

I finished restoring the 3 phase to the system and everything appears to be working as before. The Autotune motor that Jules has refurbed appears to be running in the correct direction, so we are ready to hook that up as soon as the exciter is installed and the shaft couplings are complete. There are still some issues with the Autotune dial functions: no pulses in the “1” position and I’m not getting “Shut Down” with the expected dial sequence. The Autotune motor starts running as soon as the main 3 phase breaker on the power contactor is turned on. I expect there are some hand shaking sequences between the phone relay assembly and the exciter that may be necessary to implement some of the functions.

Mike, Larry and Rod discussed antenna/dummy load issues. We hope to use some of the overhead 7/8 Heliax to feed the roof and install a ¼ wave vertical resonant around 7250 as the initial antenna. We have been using an HF-8050 receiver hooked up to a short wire on the roof and the noise level on HF seems to be low enough to allow us to work well.

Big concern at this stage is how to address the power levels on the ham bands. In tune mode, we could still get 1500 watts carrier out, but perhaps we can reduce drive and loading to allow us operate legally. Alternative is to use company test frequencies to allow use of full power or to ask for special temporary authority. Still some time before we expect to be generating RF, but hopefully that will be soon.

Rod found a draft copy of a speech that Warren Bruene gave on Sept. 20, 1980 to the Antique Radio Society. Here is some text from that speech entitled “History of Collins Broadcast” by W. B. Bruene:

The History of Collins Broadcast wouldn’t be complete without mentioning Short Wave Broadcast. I can remember working several months in the late 1930’s designing and testing a modification of our 3kW Auto tune transmitter for SW Broadcast. This transmitter used a pair of Eimac 750T’s in the final, a pair of 450T’s in the modulator and type 866A and 872A mercury vapor rectifiers. A mystical feeling seemed to come over one watching those glowing cherry red plates and the bouncing blue glow of the rectifiers. Two of these transmitters were sunk on their way to Indonesia during the early stages of WWII.

I particularly like the next to the last sentence in that paragraph; I really expect a similar “mystical feeling” when we watch the cherry red plates for our final and PA tubes and the “bouncing blue glow of the rectifiers.”