Been away from electronic stuff for a little while, been building cabinets lately. But, I'm trying to get my mind back in electrical gear again. So, transformers, and I know I've had one or two posts before, but it's the subject that I keep coming back to.... I would like confirmation or correction on a few bullet points. I'm not quoting anyone, and I'll try to use italics for my own conjecture points Increasing your PT with a higher current rating PT should allow for more headroom and cleaner output at higher levels where the old PT was stressed or exceeding limitations, but not in general. Increasing your OT size - especially in smaller amps - usually involves changing to a reduced primary load than your original. Example: "upgrading" your 15 watt Tweed Deluxe OT to a 22 watt Deluxe Reverb OT increases the headroom and firms up the bass. Is it because it's a "higher rated" OT or is it because the 6.6k allows more current to pass through the PT and power section and that is why you gain headroom? Is the end result because the OT staying cleaner, or is the PT supplying more current? Personal experience: I've used the Hammond 1750E 15-watt 5E3 OT for it, 5f10, 5F11, and Princeton Reverb, the PR being the last build. Until that one, I knew that the OT saturation must be part of the sound I was getting. The PR had amazing cleans - crisp, punchy, and clean pretty well up the dial. I used a 100mA Hammond 290AX PT -- the smallest PT I've used with that OT... the others being 115mA and 138mA. So, that tells me the circuit may have been a bigger factor than either transformer. Also, I've put a Hammond 1750H Deluxe Reverb 6.6k OT on a Harvard build. It is the absolute cleanest 6v6 Tweed amp I've built, and this is my 3rd Harvard, but first one with the 6.6k OT. Everything else is the same. So, is it cleaner because the OT is rated for 20-22 watts and "sounds" different, or is it cleaner because it's 6.6k vs 8k and it's drawing more current through the power section to keep things cleaner & tighter? I know Fender used undersized OT's back in the day to limit bass response and help the low powered speaker situation at the time. But, am I correct that using higher OT primary impedance would allow the use of lower rated PT's as well? Not looking for optimum performance, but if you had a PT that was borderline for a 4k 6L6 amp - optimum performance - would shifting it to a 6.6k OT reduce the current draw, thereby making it a lower output amp suited for the borderline PT? In that line of thought I'm thinking of the Tweed Super/Bandmaster/Pro that I think used a 6-6.6k OT primary. Please don't limit responses to my questions. Once you get away from brand preferences, I feel like transformer specs are the real black magic for a lot of people. Anyone can spend $10-20 on caps and tinker with stuff, but I think the expense and potential for catastrophic & expensive failure keeps most average people from going crazy with transformer games.