Building trust every day  Rockwell Collins Museum

May-20 ···
233D Transmitter Restoration Project

No RF, but things are looking good! Fault that caused the low voltage (660 VDC) problem has been cleared so it looks as though everything that uses that voltage and several other lower values should be happy.

When we key the transmitter, we get about 10 mils of plate current on the 807 multiplier/driver. That indicates that the keyer circuit is changing the bias from cutoff to operate. But no grid current on the 807 or the 813s so it doesn’t appear that the oscillator is working. We verified that the crystal adapter was plugged into the correct channel location and that the adapter jumpers are correct. The crystal is marked as 3636.5 and we could not hear anything on that frequency with the 8050 or 51J-4 tuned there or to 7257 (where the multiplier should put the signal.) Put a scope probe on the crystal and saw no indication of activity.

We’ll try other crystals and Jules brought in what we think is a good 837, so we’ll try those paths of least resistance next. After that, we’ll be faced with the ultimate hollow state engineering challenge: why is it always easier to get amplifiers to oscillate than it is to make oscillators oscillate?