Collins Aerospace Museum

May-11 ···
233D Transmitter Restoration Project

Got the replacement exciter bias transformer installed. Output to the filter is -334 vdc which is considerably higher than the expected -250, but the filter caps are 600 WV so don’t think we are stressing things as far as the caps are concerned. Not sure what the impact of having this level on the 837 suppressor grid and the 807 control grid when the transmitter is unkeyed, but real concern will be what level those two pins end up with when keyed.

Rod has located some early (1940) manuals for the 16F that uses the same tube lineup and 6SJ7 keyer that our transmitter uses. Hopefully that manual will provide better theory regarding the keyed condition than our documentation does. Rod, appreciate it if you would get the 1940 16F/BC-560(?) Book out before you head to Dayton.

Next step is to supply plate voltage to the 837 and 807 to see if we can determine if we get oscillation. The 208 single phase that we use for the bias supply also supplies the filaments for the 837 and 807 (and the 813s), and I think screen supplies are from dropping resistors in the plate voltages.

Next major challenge will be to determine why the plate contactor is not working for the intermediate/test high voltage. When we get RF, we really need to use the lower plate voltage on the 813s while we are tuning. Hopefully, it is just a loose connector or dirty relay contact in the power control chassis.