233D Transmitter Restoration Project
I came back in yesterday after two weeks off catching up things as home. I had hoped that the good fairies would come by and fix most of the things I left hanging, but not much evidence of that.
Rod swapped the PA output tuning network for the exciter and he has set the bar extremely high with regard to the level of restoration on the output network. He completely disassembled the network and cleaned and polished all the parts to where they are as new. He installed the â€śnewâ€ť high voltage capacitors Jim Stitzinger had located for us; we need to send the donor a letter of thanks. Jim will provide us with his information. I intend to leave the network out for all to see when they visit because it is a great example of early Collins quality. We think Collins made all the capacitors, inductors and switch assemblies.
We are still missing the big wire-wound resistors for the high voltage bleeder and meter network. I checked with Warren Fackler at Iowa Radio to see if he can locate some for us.
Quality Plating in Sterling, IL started the three chassis and parts on Friday as promised, but they wonâ€™t be finished before he starts a planned 10 day shutdown today. He said they would be first in line when he comes back around the first of the month, so we should be able to get them by July 8th, but Iâ€™m planning to really start on reassembly on July 18th. Iâ€™ll handle the Modulator tube chassis since Iâ€™ve torn it down twice and reassembled it, so I have a good idea of how it goes together and itâ€™s about a 20 minute job with only four solder connections. The high voltage rectifier and bias supply chassis will require quite a lot more work; I have detailed photos and I think they are pretty much wired per the documentation, except for the filament transformer on the bias supply chassis that will take a little creative engineering since it is a replacement; I have a template of the mounting details, so it shouldnâ€™t a major problem.
The High Voltage rectifier assembly should be fairly straight forward if we use the existing under chassis wire harness. All of the high voltage cable looks to be in very good condition except for the wires that go to the big transformer, the filter network and the six plate connection wires. Rod has provided us with a fair amount of new cable, but we may need some additional for some of the cabinet interconnect wiring; it appears to be available.
Still struggling with the power contactor assembly; the three big resistors that appear to be used in test mode are not wired as the in the 231D and the TDH transmitters so we need to understand how they worked. I have started to cut the cable lacing to try to determine how the thing worked as wired.
I still have lots to do at home so will likely only be in on Wednesday during museum open hours or when thunderstorms or heat and humidity force me to stop home project work. If everything goes as planned, Iâ€™ll be completely done with everything here by July 4th weekend, so will likely be able to spend quite a bit more time on the big transmitter after that.
| June 20, 2013