SCA-35 power transformer

I have a SCA-35 that i have been using for several weeks. It has the EFB mod installed and has worked perfectly.
Last week while working in another room and listening to music the amp suddenly stopped. When i went to have a look i found a very overheated power transformer. Investigation showed that the 2 amp main fuse was open. After a cool down i checked the two primary windings and found one winding at 10 ohms and the second at 0 ohms. No other signs of damage to the amp.
I connected test transformer to the amp and it started right up. All voltages look correct and i monitored the amp while it ran for several hours without issues. I was able to secure a replacement transformer but am concerned about the same thing happening again. Maybe the insulation in the old transformer simply failed with age. It always ran quite warm.
Anyone have any thoughts on these power transformers? Anyway to protect them??

A few things first: I am running an ST35 in the office, same transformer complement as the SCA, and it is pretty much "on" for 10 hours per day. It runs fairly cool - I can leave my hand on it for as long as I wish.

Now:
a) The unit is rated at 110 watts, or about one (1) amp. The OEM fuse was a 2A DUAL ELEMENT fuse, and if a Slo-Blo device was in-place, and actually blew, there is something serious going on.
b) For the most part, the EFB mod is a good thing. But have you actually measured the current in use?
c) Unless you have the PB028 transformer (optional 120/240 V) there is only one (1) primary winding. Whereas most units were supplied with the PA744. Check which one you have.

For diagnostics: Try to measure the actual current used by your unit. After the turn-on surge, you should be reading somewhere between 75 and 100 watts. Test your tubes for shorts, if possible.

Please report back on your findings.

Okay, so here is what i have found that might explain the meltdown of the power transformer which was a PB028 with 120/240 capability.

Nothing!

I did measurements with it running almost full out with a pair of Tanoy C8's. B+ current approx 145ma and primary current varying between 700 and 800ma ac at 120 vac depending on the music playing. What was impressive was the cathode bias voltage wandered around 20 to 30 millivolts from zero signal to almost max volume. The EFB mod is impressive. The bias voltage is down about 10% as is the B+ due to the doner transformer only having 300-0-300 vac on its hv terminals.

I am assuming that the old transformer insulation simply failed from old age. I have read here that this transformer normally run hot.

Now i will wait for the replacement to arrive.