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Apr-17 ···
233D Transmitter Restoration Project

 
This is the High Voltage Rectifier unit that Jim is referring to. Six 872s.
Lit filaments on the HV Rectifier chassis this week. Not so pretty as the PA tubes, but fairly positive results. Means the two big 872A filament transformers are good. There was some indication of tar oozing from the bottom of one of the transformers, but have run each for several hours with no heating or other problems. One of the RCA 872s has quite a lot of black material floating inside the envelope. The other five all look extremely clean after “cooking” them. Need some advice on the 872s; been a long time since I had anything that used those big beauties. The RCAs act a little different that the other three. The mercury in the RCAs appear to move back to the top of the tube envelope after the filaments get cold, whereas in the other three, the mercury appears to stay in the tube base. I vaguely recall that the tubes should be maintained in the vertical position, even when power is off, but I don’t that is a major problem; fairly sure they absolutely have to be vertical when the high voltage is applied or there may be some spectacular fireworks. I may have a couple of new tubes, but if not, we probably should get a couple of spares.

Also powered up the Modulator filament transformer and it looks good. Didn’t hook up tubes yet, so don’t know if there will be problems with the load. Chassis was in bad shape, so I tore it down and will clean it up and repaint it. Chassis is textured gray like the St. James Gray. Think that is available from Rust-0leum.

Got another Weston 301 300ma meter this week to the replace the bad scale on the grid current meter. I had hoped that the smudge on the scale was on the glass or was just loose dirt, but that is not the case; it looks as though there are a couple of mold spots. Looks much better than what we have, but still not perfect. Also looks as though the movement is off the jewels, so we struck out on having a spare, too. Good news is that it only cost $10, plus shipping. Hopefully, Jules can use it.

Moved the IT skid over and pulled up the floor in the NW corner of the room, but still haven’t found any evidence of three phase connections. There are at least three raceways under the floor, so it is likely that we will find something if we keep looking. There are still two 3-pole breakers in the panel, so I feel certain that there are still circuits in the room. Any suggestions on how we get the electricians to help? Do we need to pay for them to hook us up?

We need some recommendations on mounting the power contactor. I think it was intended to be wall mounted, but there are two large conduit fittings on the base of the box, that might be used to support it from a base. It has connections to the big plate transformer and to the power bay to distribute power.

I have pretty much backed off on cosmetics beyond cleaning up the major grime. My first priority is getting as much functionality testing done as possible. I expect to have everything clean, but will not attempt to tear down any of the chassis to fix minor paint problems, with the exception of the Modulator tube deck, the HV rectifier chassis and the Modulator filament transformer chassis. The modulator tube deck and HF rectifier chassis are chrome and will be visible through the door glass and are both fairly to easy to tear down and reassemble. The modulator filament chassis was fairly easy to tear-down, since it only has a 5 terminal terminal strip and a fuse holder, but the heavy wiring to the filaments is stranded and was difficult with my small iron but I managed to get them off without too much problem.

Plan to keep testing next week with anything that is powered by single phase 208 VAC.

I have been working on a “systems” drawing and have a fair understanding of how all the cables are connected, although I still have a couple mysteries to solve. Could use another set of eyes to help trace things.

Lets plan another get together next Wednesday during museum hours.

Jim