This procedure has been on the request list for years.
I just finally got around to doing it.
Tube amp bench test method. Example: Fender Super Reverb guitar amp.
You do not need to be a test equipment expert to perform this test.
You also do not need an expensive oscilloscope. Many 10Mhz and under scopes can be purchased for under $100. Examples: Heathkit, Leader, Iwatsu, Hitachi, B&K.
Audio dummy loads can be purchased or construct your own using a resistor on a 1/4" plug.
So watch the procedure, let me know if you have questions. I also have a quick reference diagram .jpg available. E-mail me for that. I am doing my best to share this knowledge.