Building trust every day  Rockwell Collins Museum

Jun-4 ···
233D Transmitter Restoration Project

Got a NROS (that’s New Real Old Stock) 872A yesterday and plugged it into the HV rectifier to condition it this morning. It was in the original box with US Navy markings and was also known as a V42A and was manufactured by Sperti of Cincinnati, who I had never heard of, but Jules says they had manufactured some parts for the ART-13. Tube came nicely with no flash-over so we now have a complete set of what appears to be good tubes.

Lashed up the choke input filter parts and brought them up with apparent problems. The voltmeter now reads 4200 volts although we need to “calibrate” the VM circuit. Without the filter network, the output voltage was 4100 volts; I expected with the choke installed, the voltage might be a little lower, but I expect that the output caps are causing the higher voltage.

When I cycled power, I did notice some notice some brighter blue flashes on some of the tubes likely do to the increased load imposed by charging the capacitors. Also noticed that one of the 872As had developed some minor flash-overs. These went away, but concern me because I expect that will persist with modulation peaks. This particular tube had been somewhat difficult to bring up during conditioning, but had appeared to have become very stable after the conditioning process. This doesn’t appear to be a major problem; doesn’t cause any remarkable loads and doesn’t make the voltmeter level change at all, but I think the condition does indicate potential problems with the tube. I’ll experiment more before we tear down the conditioning setup, but I’ll likely just sub our known good tube.

We will use the setup to apply high voltage to the modulation transformer. We’ll apply high voltage to the center tap of the primary and attach high impedance loads( 5 or 10) to the mod tube plate leads and apply high voltage to one side of the secondary and use a high impedance load to the final PA tube plate connection. We’ll ground the transformer case so that we can make sure we don’t have breakdowns in any of the winding. Any thoughts or comments appreciated.