There is one piece of test equipment you should have on your bench when building or repairing a tube amp. It is a AC ammeter. I use it religiously whenever I first power up a tube amp for repair or when I build a tube amp like. Let me give you some examples. A stock ST-70 properly biased will pull about 1.7 amps with a 5AR4 tube and a ST-120 biased at 55ma per tube will pull 2 amps. Once you power up your amp, you can monitor the AC ammeter and if the current rises or drops, you can quickly see there is a possible problem. I just tested a amp with a 5AR4 tube, biased it and I noticed the AC amps kept dropping, I rebiased the tubes and the same thing happened. I checked the B+ and sure enough it was slowly dropping. The new 5AR4 tube was bad.
I have a metered Variac on my bench to monitor the amp and I also have a Kill A Watt plug in digital "meter" that will measure current, watts, volts and killowatt hours. They sell on ebay for about $21 and is well worth it. Here is a seller on ebay that has them for $20.49 with free shipping at http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=360458834329
Note: I am not affiliated with the seller at all, I just wanted to pass this along.