233D Transmitter Restoration Project
Two items completed on the list of 21 tasks from last week, but added two more, back to where we were 7 days ago!
Not really. Jules did get the PA grid meter work done and will bring in the Telco relay chassis so we can do further check out.
Jules was fairly certain that Autotune shaft between the PA grid and the PA output network was installed when we got the transmitter and I thought that was the case, too, but I could not recall removing it. I checked the images from before it got shipped from California and one very clearly shows the shaft was not installed so I think we can close the book on that mystery.
One of the new items is that the time delay circuit in the power control system may not be working. The TD is supposed to close 30 seconds after filament voltage is applied to allow the tubes to reach operating temperature before high voltage is applied (particularly important for mercury vapor rectifiers) I had incorrectly thought that R3-6 was the time delay relay and had determined the coil appears to be open. Turns out that relay is the “Remote Control Autotune Interlock” relay and the real time delay relay is R3-7. So we have a bad relay, but probably not so much problem as would be the time delay relay. I will bring leads out from the TD relay and determine whether it is functioning properly and if not, it appears that it can be disassembled and either repaired or allow installation of new TD circuit. Not a show stopper.
Other new item is that the audio level meter in the modulator meter panel is missing the cable that plugs into the cabinet. This is another “multi-meter”, with manual selection similar to that used in the power supply for line and filament voltage. The schematic is confusing for the input measurement, but Jules says it is more likely that the Western Airlines draftsman is correct and am the one confused!
More time this week on the 175R-3 control chassis. Brought in an old TEK 465 and was able to verify that the Autotune phone dial appears to be working correctly. Next step is to make sure we are getting the proper drive levels to the TELCO rotary relay.
Mike has a good start on getting the control cable from the power control system to the contactor assembly done so we can check out that system. He had to go to an important meeting related to his day job. Guess we all have to establish priorities!
Peeling the onion sometimes results in tears, but only for a little while!
| April 2, 2014