I'm bringing back Fisher, Marantz, HH Scott, McIntosh equipment brands that are up to 40 years old vintage.
With tubes inserted that I'm confident that are good I connect several voltmeters connected to each bias pot or resistor to make sure that none of tubes will significantly drop or increase bias current during voltage increments. There's a slight risk of damaging tubes, but it's part of business give or take. Blind replacement of DC supply caps (assuming they're all bad) before-hand usually never hurts and prevents from tubes being destroyed especially when I'm dealing with client's equipment that needed be restored.
Old coupling caps usually create less of a problem if any. quick test for short is usually enough
Now about increments and waiting time. I don't think that it's necessary to wait 30min per 6V increments. If I did that, I'd have to charge client at least a grand or couple depending on unit complexity and keep unit for a month or couple. I simply slowly bring it to the point when something begins to fail or to the operational voltage AFTER REPLACING ALL DC CAPS. Voltmeters or DMM testers I connect to each tube bias pot or if self-biased to the bias resistor to measure proper voltage. From voltage as you know you can figure the current and if you can't you'll need to go via basics of electrical circuits.
Current = Voltage/Resistance
Similar methods I apply to the vintage solid state equipment. I would usually use NTE replacement transistors instead of original or NOS to run these tests. I wouldn't be worried if I fry $1 worth power transistor instead of $15 one.
With tubes inserted that I'm confident that are good I connect several voltmeters connected to each bias pot or resistor to make sure that none of tubes will significantly drop or increase bias current during voltage increments. There's a slight risk of damaging tubes, but it's part of business give or take. Blind replacement of DC supply caps (assuming they're all bad) before-hand usually never hurts and prevents from tubes being destroyed especially when I'm dealing with client's equipment that needed be restored.
Old coupling caps usually create less of a problem if any. quick test for short is usually enough
Now about increments and waiting time. I don't think that it's necessary to wait 30min per 6V increments. If I did that, I'd have to charge client at least a grand or couple depending on unit complexity and keep unit for a month or couple. I simply slowly bring it to the point when something begins to fail or to the operational voltage AFTER REPLACING ALL DC CAPS. Voltmeters or DMM testers I connect to each tube bias pot or if self-biased to the bias resistor to measure proper voltage. From voltage as you know you can figure the current and if you can't you'll need to go via basics of electrical circuits.
Current = Voltage/Resistance
Similar methods I apply to the vintage solid state equipment. I would usually use NTE replacement transistors instead of original or NOS to run these tests. I wouldn't be worried if I fry $1 worth power transistor instead of $15 one.