• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Filament transformer questions

I have some filament transformers that have me scratching my head some. I got these from surplussales.com. These are the (TP) 19-P-33.

The website says they are 1.2a, but I have them and also have a couple others from their website that are rated for higher current. The thing is the 19P33's are much larger than the 2-4a FT's. They are quite heavy and the wiring isn't puny. It would see to me that they might really be rated for more and mis-marked.

How does one test to see how much current a given transformer can deliver? Do you set up different loads for different currents and measure voltage for regulation and call it at a certain spot? I think I've read that the industry rates them for a specific temperature increase.

My second question pertains to how much abuse can a FT take. For example, can you hook up tubes that draw 6.3v @ 2.4A on a 2A FT? What percentage abuse would be fair/not-fair?
 
Connect a 6AS7 and see how much the voltage drops at 2.5A (I keep one handy with clip leads just for testing transformers). If it drops 0.6V that's 10%. < 10% means that the transformer is dissipating less than 10% of the 15 watts delivered...

Small transformers will have too much voltage drop before they're in danger of overheating. Large ones are limited by heat before voltage drop is a problem.