Thanks for the comments on your Ace and Studio22. Sounds like the high heat might be normal.
I did an experiment the other night with a fan located underneath the power transformer and a thermocouple attached to the outside of the transformer. After one hour the temperature had stabilised to approximately 50°C and at two hours it was still stable at 50°C. I was still able to touch the transformer without (too much) discomfort so I think that's probably the solution.
Here are some more details about the rebuild that may be of interest.
I had to try to work out what specs to wind the power transformer. It is notoriously difficult to get specifications from Mesa so in the end I had a look at the Hammond transformer catalogue as well as looked at the specification for the higher output fender amps to determine what the spec should be. We chose 345 VAC @ 400mA for the the HT secondaries with a 52 VAC CT for the bias and 3.15 @ 6A for the heaters with a ground CT. I'm happy with the voltage that we get with 445 VDC B+ with 220 VAC primary (mesa specify 448 VDC) and with the Tung sol KT66 tubes biased to 40mA. I am getting -52 VDC on the bias which is on spec. The primary taps to make it export spec are 117, 200, 210, 220, 230 and 240 VAC and I've bought a Carling selector and voltage plate from TAD which works very well and looks very similar to the original mesa/fender style export transformer voltage selector plate. My guy who rewinds the transformers is fantastic. I have got him to rewind a number of transformers for customers amps that have had problems or wanted conversions toto 220 VAC. It costs a lot of money for us to import US transformers due to the weight of the items. In fact I looked at the price of a Mesa Mark II export spec transformer from TAD (Germany) and the price of the transformer (US$327) and shipping (US$125) was a bit of a shock! It took me a long time to find my transformer guy but I'm really happy with the quality of his work and the price is more than reasonable.
I should explain further regarding the status of amp when I bought it. I bought it off US eBay as a non-working project. The vendor said that they weren't sure what the problem was so it was a bit of a risk. As mentioned, soon enough I worked out that the transformer was fried and there were a significant number of mods and "child-like" repairs so I was determined to bring the major components of boards back to original spec as well as make it a little bit more practical by installing a export spec transformer and a 25K wire wound bias pot so different output tubes can be used. I have also replaced all the electrolytic capacitors on the power rail, bias and cathode bypass and replaced all of the tubes as they were a mix of various brands and ages. There was a lot of small things to do such as replace the Middle pot which had been replaced with some nondescript Chinese pot as well as replace all of the replacement resistors with Piher resistors which is what Mesa we're using back in the 1970's. The pilot lamp had to be changed to a 250 VAC unit as it was only 125 VAC and would have burned out with the higher transformer voltage.
These amps is have a reputation for being a hum factory and so while the chassis was out I took the opportunity to clean up all of the ground points to make sure that they were good contacts. It is interesting that there is a lot of misinformation and mythology on the web about the these amps. By taking a logical approach to cleaning all of the ground points at amp is reasonably quiet at all volume levels. The reverb is a little bit noisy but not a distraction. Overall, it's a very nice sounding amp, with enormous tonal possibilities but incredibly loud!
The other thing was that the chassis was installed in a slightly later Mark 4 cabinet and the mounting holes could not be aligned correctly and so they had just put some bolts with big washers through the sus-4 shock mounts which made it ugly and impractical as the bolts could not be tightened properly. So I had to remove the sus-4 shock mounts, fill the holes, and then re-drill where the holes should be for the chassis mounts. Of course to do this meant retolexing the cabinet - the tolex came off reasonably easily but to remove the original glue was a big job. Also, I decided to re-drill the speaker mount points so they had cage-like retainer mounts for easy installation and this is what they had originally anyway. So the job got a lot bigger than what I expected.
The funny thing was that the amp cost US$425 (not working remember) and the shipping and customs fees cost US$395 to get it to Bangkok, Thailand. I have calculated that I have put about US$1200 total into the amp so far and so I've probably overcapitalised by US standards but here in Thailand it is a very rare amp and if I wanted to sell it I can probably get about US$2000. Importantly it was a great project and I always get to learn something new. In fact, I ended up making a layout diagram based on the original schematic so that I could reverse engineer and make sure that I had everything in the correct place and it should work when I started up for the first time (It did by the way using a dim bulb tester of course).
I will try to upload to photos
