I bet this has been thought of before. But just in case...
So the standard bias pot in the ST-70 is 10K. But if the wiper lifts, the tubes aren't biased and start glowing. My idea is simple: take a 20K pot and tie the wiper to both sides of the pot through two 10K resistors. So if the pot is in the very center (assuming it's linear), the total resistance from one end to the other would still be 10K. However, if you move the pot to one extreme or the other, according to my calculations the resistance would drop to 9.33K. I don't think that's a problem. But when the wiper lifts, it would see half of the maximum bias voltage.
Is this a good way to eliminate the problem of failing pots? Is it the easiest?
Kyle