Collins Aerospace Museum

Apr-24 ···
233D Transmitter Restoration Project

Three of the high voltage oil-filled capacitors used in the HV power supply.
Tore down the Modulator filament supply (407F-2) because there was quite a lot damage to the chassis including heavy rust. Took the chassis down to bare metal and primed it and then applied gray “textured” coating. Interesting because this different from the rest of the gray chassis and interior of the cabinets; similar surface to the St. James Gray on the cabinets but considerably lighter. Result was not perfect, but the rust is gone. No load voltage was similar to that for the PA filament supply so it is probably good, but have reassembled the Modulator tube deck and will check it along with verifying the wiring in the modulator bay.

Reassembled the PA filament supply (407F-1) after touching up the chassis coating clean up. I had removed the PA interlock relay that is on the chassis and cleaned it up but haven’t done any functional testing. I have found a Rust-Oleum gloss gray that appears to match the transformers fairly well.

I bought some cable markers to ID wires as I verify continuity.

Pulled the Low voltage power supply (405J-1) today. Larry Tjaden was there and pointed out that one of the plate transformers appeared to have been replaced. While attempting to identify the parts in the supply, I noticed that there was quite a lot of difference between the parts list and the schematic. The schematic appears to depict the as-built state of the supply. Also determined that there were no 866As available. The parts listing indicated that 4 866As were used in the LV supply and 2 in the Bias supply. On the LV supply, there were two tube bases that included two diodes and a resistor in place of the rectifier tubes. So someone had “solid-stated” it at some point. Likely had originally used dual plate rectifiers such as the 5R4. The smaller tube sockets indicated that the supply had been built that way rather than with the larger 866As.

Since there no 866As, I brought in a couple of 3B28s which are commonly used to replace the 866As. When I first plugged in the tubes, it appeared that the filaments were not being lit and the swing on the ammeter indicator that no power was being applied. But after applying some deOxit and waiting a few minutes, the tubes heated, so apparently the supply works. As soon as I can makeup some additional cables, I’ll apply the plate voltage and check out that part of the supply and check out the apparently lower voltage side. All of the oil-filled caps in supply make the ohm deflect when the leads are reversed, so I think they are not likely to be shorted.

I talked to one of the electricians today and he said that we would need to get a work order to get the three phase connected. He said he is not sure that the wires are still connected to the breakers in the box, but thinks that it is possible. He said we should contact Melissa Loney to make arrangements for the work. Not sure about the spelling since I don’t have access to the on-line phone book.

Larry said he will talk to someone about getting a three phase supply from test equipment.

I’ll remove the Bias power supply (405K-1) next week. It looks pretty bad because the filament transformer has obviously been replaced and it (the transformer) is just sitting loose on the chassis. Surprised it stayed in place during shipping.

Lots of work remains, but we should be able to complete of the initial check out by the end of next week.