Collins Aerospace Museum

Apr-26 ···
233D Transmitter Restoration Project

Finished check out of the Low Voltage supply this morning. When the 3B28s first came up, there were some scary swings on the ammeter, but it then settled nicely. One of the 3B28s shows some color, but the other one doesn’t. Need to check that out, but I expect one of the tubes may be bad. I think I have another NIB, so I’ll try that next week. The tube side puts out 628 Volts, no load and there are three lower voltages on the taps on the bleeder resistors. The side of the supply that has been “solid stated” puts out 65 volts, no load. No arcs or sparks from either side of the supply and nothing gets hot except for the bleeder resistors. So everything looks good.

Need some help with whether or not we need to use 866s in the this supply and the bias supply or to replace them with 3B28s. Think we should replace the solid state devices with tubes. Think 5R4s will work.

The 628 volts is used for the 813 screens in the exciter and the 807 plates in the speech/audio driver assembly. The 65 volts appear to only be used by the test key. Haven’t traced the system for where the other low voltages are used. The modulator bay has a supply for the other voltage used in that bay. I’ll check that supply next week after I come up with bleeder resistor to the replace the one that is open.

Also plan to pull the bias supply from the power bay and test it next week.

I think I can also do some testing on the exciter and the Phone relay assembly from the RF bay.

Still lots of functional testing to do but the rest will require installing in the racks and using the system wiring.

Pulled up more floor tiles and still didn’t find any 3 phase circuits.