233D Transmitter Restoration Project
We attached the HV rectifier to the plate transformer and started “conditioning” the 872As. Up to about 14% on the Variac (we think about 600 VDC; we still have to hook up the voltmeter) we get fairly uniform, nice blue glow on the tubes. But after that, one of the tubes additional wisps of blue radiating around the plate/anode cap. Very stable and goes away if the input is reduced slightly. Also goes away with a small increase in voltage, but then comes back somewhat brighter. I don’t think this is “flash-over” which I think is more of an arcing. I think this may be an indication of a loss of vacuum seal in the tube. This tube also did not show any sign of filament lighting as the did the other five. The tube did get warm to the touch, so not sure if that matters. We have two spares, but one has quite a lot of black material on some of the elements and I expect that will resulting in arcing. We’ll try the other tube we got from Al, k0vm, last year. It is marked with a label as “new” and is in the RCA box. One of the leaflets in the tube box is dated 1934, so it may be similar vintage to the 872s in the Byrd transmitter.
I’m a little surprised about the blue; I remembered that MV rectifiers always had purple or violet haze, but it has probably been 50 years since I saw any so my memory may have faded. Mike has some pictures; maybe he’ll share them.
I’ll hook up the voltmeter next, so we can watch the real output. Just using the new bleeder/voltmeter multiplier board and nothing seems to be arcing or sparking but we have a long way to go before full output. Also do not have any of the HV filter parts attached. I have applied low voltage to the inductors and the caps and there does not appear to be any more problems. But I would like to make sure the Rectifier is working properly before we complicate the process.
Jules has finished the cleanup on the Autotune motor including fab’ng a new top oiler tube. He has also found a source for the original U joints for the shafts, but they are pricey. I suggest we check with In Tolerance to see if they can machine something for the project. I have lost the contact info. I think Lawrence and Rod may have that.
does the exciter have a U-joint and a short shaft? I vaguely recall there was something on the coupling.
If everything goes well, I expect to start moving everything back into the power bay in two weeks. You and Mike had some discussions about routing the High voltage cabling between the plate transformer and the power bay with regard to sleeving and grommets. I’m also thinking we might want to reduce the cable run from the plate transformer to the power bay to about 15 feet. Also think we should move the plate contactor up about an inch to better clear the plate transformer cover. I’d like to get together to talk about it at some point.
| May 23, 2014