Does your power transformer seem to you that it's running too hot?
Here's a method, from an NRI course book, for determining the temperature of a transformer winding. Basically, it's just measuring the resistance of a winding cold, and again while hot, and then using the following formula:
T(hot) - T(cold) = [[R(hot)/R(cold)]-1] x 235
Temperatures are in degrees centigrade, resistances in ohms.
Most digital ohm-meters will only read resistance to the nearest tenth of an ohm. This is not accurate enough for a winding of only a few ohms. But the high-voltage winding of a power transformer usually has a resistance of 3 digits, so you can measure it with sufficient accuracy. But if you have some lab grade equipment that will measure resistance to the hundredth or thousandth of an ohm, then you could theoretically use this method with any winding.
Here's a step-by-step easy method for a full-wave transformer as found in common AC tube type receivers.
 make sure your radio is stone cold and has been turned off for several hours.
 remove the rectifier tube and insert your ohm-meter probes into the plate pins in the empty socket. You can look up the tube at http://www.nj7p.org/Tube.php
to find the correct pins. Remember to count the pins counter-clockwise because you're viewing from the top. Measure the resistance and write it down. This is the "cold" resistance of the high voltage winding of the transformer.
 put the rectifier tube back in the socket and turn on the radio. Let it play for an hour or so. Longer if you want.
 now turn off the radio and quickly remove the rectifier tube again. Careful! It will be very hot. Use a mitt or something to protect your hand. Quickly measure the resistance between the plate pins in the empty socket again, just like you did in step 2. Write down the value. This is the "hot" resistance of the high voltage winding of the transformer.
 now, according to the formula above, you divide the hot resistance by the cold resistance, subtract 1, and multiply the result by 235. This will give you the temperature difference
between hot and cold. Simply add this difference to the room temperature (centigrade), which we assume is the same as the "cold" winding temperature, and you will have the "hot" temperature of the winding.
The UL code states that the maximum temperature rise
of power transformers be less than 50 deg C. That's 122 deg F. So if your room temperature is 72 deg F, then the maximum allowable winding temperature would be 194 deg F.
I've tried this on several tranformers and seem to get reasonable results. The temperature obtained though, is always higher than what I measured the outside of the transfomer to be with a thermocouple. No doubt there is a temperature gradient between the winding and the outside of the transformer.