use this opportunity to increase the capacitance of the original caps? I have 100uf caps that I will replace for the safety of the transformers in my 1969 MC275... why not increase the capacitance 50% to 150uf given that ncreasing power supply capacitance seems to be a pretty common upgrade?

Anybody done this or know why I shouldn't do this?

If you are going to keep it original looking with twist-loc cans about the best and biggest you can get are 100x100@525V from AES. These are the ones that I use as replacements, about the most you can expect is a slight tightening of the low end (less boom) from a stiffer power supply.

Terry's right that there's not a lot of benefit to upping the power supply filtering on these old Macs. I've kept my MC-225s at the same values when replacing them. I consider P/S replacement as a basic maintenance and safety item for these amps.

I did pay attention to the values, too, in the coupling caps. This is where you'll see the most audible improvements.

Again, I'm not one to change values and prefer to keep things the same as they were designed. Those guys at Mac spent a lot more time working out those cap values, who am I to go and try to rethink it?

Cheers,

David