[Heathkit] IO-12 Vertical Drift fixed

[Harry Vaught, KT4AE]

Thanks to Ed, K6UUZ for pointing me in the right direction.

There's only one coupling cap from the previous stage serving both sides 
  of the vertical amp, so I doubt that that was it, but it was one of 
the dreaded Black Beauties, so I replaced it anyway.  There's a bypass 
cap on the grid of the 'B' side of the 12BH7 vertical amp (I mistakenly 
said "12AT7" originally, thinking of my OS/8 which is full of 12AT7's) 
which was apparently leaking when hot.  It's right under the barrel of 
the CRT and looked like it had suffered some from the heat.

Anyway, it's holding steady now.  The SX-101A still affects it, but
there's adjustment to take care of that now.

Thanks again to Ed for making me take a closer look at the input side of 
the vertical amp.

Harry, KT4AE
Maryville, Tennessee