233D Transmitter Restoration Project
We hooked up the big 3-phase Variac to the plate transformer and checked the secondary outputs from 0 to 210 or so and all three windings look good with no arcs or sparks or even groans. I used my Jennings high voltage meter and we are getting around 6400 volts on each secondary and half that to the Wye connection. The Jennings says it is peak kilo-volts and in the balanced mode, I expect that is really to peak to peak. I expected the outputs to be around 2KV RMS, so I think we are likely in the ball park. Since we are using a six tube doubler, that should get us close to the expected 4200 VDC for the plates.
I finished a new high voltage bleeder/voltmeter multiplier board. I used 32ea Ohmite 5K 10W silicon WWs to replace the 4ea 30K 80 W WWs that were open. So we now have 160K in the bleeder rather than 120K. That should reduce the heat quite a lot to prevent burning another big hole in the board, without causing regulation problems. Used the other 18 5Ks to add to the remaining good 80 W WW in the intermediate output.
I replaced the open 50K 1% 50 W in the voltmeter circuit with 8ea 27K 2W carbon comps that I selected for the low end of the tolerance and the R came up just slightly over 50K. Not very elegant, but it should be functional until we can find exact replacements.
Jules found a set screw floating around in the Autotune motor. Might have been the reason there was some â€śdragâ€ť when it was upright. He has lubed everything and replace the cable sheathing and is painting the case so it will look as new.
Next step is to hook up the HV rectifier to the plate transformer and â€śconditionâ€ť the 872As to prevent flash-over, as described in the old RCA transmitting tube book. As soon as we get Purple Haze, weâ€™ll likely turn down the lights and enjoy the show. Safety glasses, appropriate fire extinguisher and maintaining a reasonable separation from the hardware will be required.
| May 14, 2014