From the "thought i'd seen it all" department, this has gotta be the first problem I've ever seen caused by the HV being
too high in a BW set. Color sets, yes. But never a BW before this one.
Anyhow, if adjusting the horiz. drive hasn't reduced the HV sufficiently, it's easy to cut back the gain of the output tube itself (the 6AV5). One method is to put a resistor in series with the cathode (say 100 ohms as a ballpark starting value). The other is to reduce the screen grid voltage (on pin 8). This is the method I would try first. Assuming you don't have a resistor decade box or a resistor assortment on hand, go to RadioShack (ugh
) and get a card of 2.2K half-watt resistors. Locate the 5.6K screen grid resistor R84. Open one leg and insert a 2.2K resistor in series with it. Bring the set up and see what the HV reads. This will give you a ballpark indication of which way to go with R84, ie., whether it needs more resistance or less. If it needs more, add another 2.2K in series. If that's too much, you can make a 1.1K by paralleling a couple of the 2.2K.
The caveat is, if you succeed in getting the HV down and the arcing cured with the set at full line voltage, the width may be reduced too much. I'm betting the width will still be sufficient. If it's not, then a new plan of attack is in order. oc