The ESP Guitar Company

A multimeter should do it. What amp?

6505+ 112 combo. I want to swap the stock 6L6s for some EL34s or EL34bs. I'm picking it up tomorrow and looking to switch right away (haven't been into 6L6s in a long time).

Make sure whatever you get, it can handle well over 500 VDC. Most decent ones will, but I don't know if I'd trust anything too cheap. For about $40-$50, you can get a digital meter that will be about as accurate as a $400 meter. It just won't be as rugged nor have as many features (that you probably won't need, anyway.) My $40 DVOM I bought for home use (from Lowe's or Home Depot, I forget which now) is pretty darn accurate when it comes to reading bias current, plate voltage, and resistor values. I even A/B'd it with the Fluke 83 V I have at work, to be sure it was up to the task.

the test points on a 112 6505+ aren't truly bias test points per tube, and AFAIK is really a fixed bias amp, even if it has a bias adjustment knob (I don't think these combos do, though). Also, the combo is not switchable to EL34's, AFAIK?