Hi John,
He isn't fixing this amplifier alone and he mentioned he is working to get an oscilloscope. Go back and read.
As far as cheap meters being accurate, hogwash. Outside the lab I check meters against an HP 34401A and an HP 3457A - calibrated. I have an RFL calibrator as well that I use to transfer the accuracy of the HP meters to others I check.
The main problem cheap meters have is that they use cheap metal film resistors that do drift. Often they are out from range to range so that the one pot can't bring them into tolerance. A real meter uses a single ceramic unit that has the low TC resistors deposited onto it (they now track with temperature) that also has a low and controlled capacitance.
I'm sorry, but I have a very low confidence in your calibrator, or it's use now. Try and do a real error budget for a cheap meter, then you tell me how many digits are effective. Many meters are 2 1/2 digits and "something" that mislead people.
The other equipment a person uses on their bench affects how well they can work. Don't strive to see how little you can spend while claiming any sort of accuracy - or even repeatability. There is a damn good reason why $450 + hand held meters exist. Even more so why $1K + can be spent on a bench meter. They are accurate and they hold their calibration very well. Performance is designed in, not just hoped for as in the cheap meters.
Variacs. If you don't use one, you just can't get it. They can be had for $20 on Ebay, more for better models. I have a few and last year picked up a B&K 1655 for less than $100 in Canada. If you don't have one due to cost, you're only making excuses.
Honestly John, if you are charging for your work, and use cheap instruments and improper test procedures, you maybe should close up shop. I feel very strongly about that since I have to clean up after happy souls who hope they are doing good work.
Last comment. If you charge for work on audio equipment and you don't have a THD analyzer, you are incapable of even knowing if your work is good or not. I hope to heck you have a half decent bench John. You actually do need that stuff, and I do mean need. If you can't see why, you really do need to close up.
Are you seriously suggesting in line bias current calibration on an amplifier that is clearly latching up is a good idea?
What the hell are you talking about now? I was very clear when I said you can take measurements at partial line voltages before things go to pot. Read the post.
-Chris