Okay, we're not as close to done as I thought. Cleaning the tuner a second time eliminated most of the crashing. In the course of doing more systematic voltage checks, I found two burned resistors on pins 6 and 7 of V4, the 6AU6 2nd video IF amp. (How did I not see those before?!?)
That's good, but I still heard a little crackling when warming up. Just for kicks, I powered up in total darkness and, during the initial surge, noticed a wee twinkle on the socket of V17, the 6AU6 2nd audio IF amp. When I scraped & probed that area with a dental pick, I discovered that the socket had arced and burned holes in two spots: between pins 5-6 and pins 6-7:
Gack. I dug out the burned holes as best I could with the pick, and powered up again. thinking I could fill the holes with epoxy if my surgery had removed all the carbonized material and there was no arcing across the air gap. This time, the arcing was brighter, so that socket's too far gone to save with a quick fix.
That'll be the end of voltage checks until I order a new 7-pin socket and install it. Meanwhile, I'll take a closer look at other resistors & sockets. Perhaps it's not a coincidence that I found Bad Things on pins 6-7 of two separate 6AU6 tubes employed as IF amps (or maybe GE just used cheap sockets).
Phil Nelson