ctc 15 combo

[sampson159]

got the call today-are you interested in an old tv? the 15 combo on ebay. of course it was robbed-no speakers,some tubes missing. got it home and did a slow start for a couple of hours. set played,sans a vertical issue. bad pot in
the centering. glad i got 3 on last order. set plays! decent picture,all 3 guns are
strong. a little gassy i think. shut it off and left. approx. 2 hours later,turned it on and the red gun went south. can get enough red to make a so-so picture with the screens turned down. the screen control for red does nothing. my crt tester checks bad-i am not too sure. when the set is turned on,it displays a nice red screen as the high voltage increases. when the horizontal spreads,the red decreases. are these old roundie crts that volatile? could it be something else? any help would be greatly appreciated.