Good morning Clark Et al,
That Mica is a new one for me.? This is the first I've heard of one failing that way.? Will enter it in my log of can bees.? Thanks all for the interesting conversation.
Historically, the most common reasons for VFO drift or frequency change are listed in sequence.
1.? The dog bone caps C121, 123, and 124 pealing.
2.? K2 pin 12 contact.? It carries no current depending on contact wipe to maintain contact.? It must be cleaned annually, or sharp changes can occur.
3.? The 6AQ5A cathode is used to switch the radio from transmit to receive and back.? It is run at the heat margins, exposing K2 to excessive temperature.? A heat dissipating shield should/must be used on the tube.
4.? Incorrect back lash adjustment when restoring the VFO:? Should be 2 teeth.
5.? The VFO should experience little or no drift at the band center and up to 300 cycles at the band edges within the first 10 minutes.? Those are design parameters assuming QC was careful.? After 10 minutes, you could tune an SSB signal, go on vacation and upon return participate without retuning.? ?
6.? There was a change submitted to mitigate the progressive natural 300 cycle drift to the band edges by mechanical VFO and PTOs but rejected because tubed radios were near EOL and digital VFOs would relegate mechanical VFO/PTOs to history.
Kindest Regards Jim K9AXN??
