233D Transmitter Restoration Project
Mike and I finally found the clue to the â€śmissing phaseâ€ť for the RF bay; turns out there is a relay on the Telco relay chassis that sends power to the PA filament supply and exciter. Jules is refurbishing Telco chassis, so Mike fabâ€™d some neat jumpers and we used those to simulate the relay and now everything appears to work correctly. I also plugged in the fan for the power bay and it works surprisingly well and is fairly quiet. I need to replace a broken fuse holder in the modulator bay so we can check out that fan, too. Still major concern with how we handle cooling air for the RF bay. The top back cover (one with the nameplate) has a small number of louvers and the bottom cover has louvers similar to those on the Mod and power bay. Interesting part is that the Mod and power bay lower panels have retainers for filters, but the RF bay panel doesnâ€™t even have holes for filter retainer hardware. So it seems reasonable to think that the RF bay never had any powered ventilation. Doesnâ€™t seem likely that convection cooling would be adequate when the finals are loaded to full 3 KW carrier out. The output network extends fairly close to the rear panel, so I expect that was the reason fans like those used on the power and RF bay were not installed. Think we should fab a housing to mount outside the cabinet over the louvers on the upper panel.
Mike will install the control cable between the power bay and the power contactor so we can check out the big plate transformer contactors. Weâ€™ll have to defeat the door interlocks to make this work, but they absolutely have to be enabled before we apply any high voltage from the plate transformer.
In spite of the fact that I labeled all the wires in the HV rectifier chassis before it went to re-plating last year (and took pictures), one of the wires was apparently labeled in error. The wiring is fairly simple, but since high voltage is involved, I need to make sure I get it right. I want to get the chassis reinstalled so we can â€ścookâ€ť the 872A (Mercury Vapor rectifier tubes) and hopefully heat up the potting material in the transformer enough to get the top cover back on. Long story; stop by if youâ€™re interested and I tell you the sordid story. (Mike edit: Iâ€™m going to get a bigger clamp and a heat gun and try to get the lids back on without having to rely on the transformer getting warm enough to soften up the potting material).
The wirewound power resistors in the high voltage supply bleeder network are still a problem; but it turns out that the old Allen Bradley division of Rockwell Automation operated Milwaukee Resistor that specialized in those resistors. The Dale division of Vishay has current data sheet for those parts so now it is just a matter of finding stock on what we need and finding out what the ransom will be on those big beauties.
| March 20, 2014