Finally got a trace! Turns out that the open cathode resistor I replaced that I thought was supposed to be a 2.7k was actually supposed to be a 39k, so after rectifying that (with a 33k), and replacing the incorrect bias resistor, it lit up like a charm.
After that, I put a sine in the X & Y, and fiddled with the bias controls until I got maximum linearity. The sweep & trigger is a little wonky, so I think I’ll run some tests with an external sweep generator to dial the amp sections in first, before I tackle the sweep. Besides, Benton (who’s scope this is) mostly only uses X/Y mode, so that’s more important.
There is some burn-in visible on the CRT, I may poke around eBay to see if there’s a replacement that’s available and inexpensive. The filter caps in the power supply are shockingly good, but I may replace them anyway, at least the paper ones.
After a congratulatory sip of Bourbon (4 Roses, one of my faves), I realized that all the troubles in this scope stemmed from bad 39kΩ resistors. I wonder if there was a bad batch, or they were all just under spec’d? In any event, I’m going to replace them all, and probably up the rating to 2W, just to be sure. I may also replace the 68k resistors that have drifted as well.
Here it is triggering on a 100kHz square wave, not bad!