I peeked at the schematic (from
http://www.earlytelevision.org/image...1_telaides.pdf ) and your set looks very similar to the Admiral 19A11 that I'm finishing up.
Like your set, mine had previously been partially recapped. Based on the appearance of those replacement caps, that work was done a long time ago, perhaps the 1960s or 1970s. The "newer" caps in my TV were plastic-coated cylinders, similar to the infamous bumblebees, but with different colors and markings. I assumed that they were the same junk -- paper caps in a plastic shell -- so I replaced all of them, too.
Since you have lost voltage on the plates (pins 2 and 5) of the vertical output tube (V15), I'd start by checking the components connected to that tube, particularly capacitors, and especially any newer caps installed by someone in the past.
A sudden change (loss of raster) suggests that some component failed. This is not unusual in restorations. Some component was marginal in the first place, and it croaks after an hour or two when exposed to voltage again. Capacitors (including micas in deflection circuits) are likely suspects, but resistors can fail, too.
Other possibilities include a funky tube socket, an intermittent ("cold") solder joint, crumb of dropped solder, bent component lead that makes a short circuit, dirty potentiometer, or a wiring mistake. When a set has been worked on before, you can't assume that all of the work was correct.
It would be easier to diagnose your problem with an oscilloscope, but it should be possible using your brain and a multimeter, although it may take longer.
Phil Nelson