OK, this is what I have discovered lately, toss it or use it.
I am realizing that certain OTs like certain power tubes. If you all are into this then cool, but if not then read on.
I used to think that it was an primary impedance thing entirely, but now I think it is a steel thing, as well, and maybe even wire size within the OT coil. Eh?
I can tell you I am not capable of teaching a class on this, but I have at least developed a 'taste' for certain combinations - particular power tubes and particular OTs, and this is what I want to share/discuss here. In fact, I think there could be a chart made of some of the combinations and it could be helpful.
My Hammond OT has a primmary of 7600 ohms and pretty small wire, certainly smaller than the #32 guage used in the TS OT. Apparently this wire size is a pretty quick compromise: smaller frame/smaller wire. There can be exceptions to this, but it is not typical to find them.
OK moving on to the combinations that I am liking with either of these two OTs. First up is the Hammond. I positively hate the J/J 6V6 with this OT. When I first ran with these I thought they were actually cool with it. But now I am very clear that that was a mistake on my part. The tone and general grind of these tubes in this amp really started to sour me on the J/J 6V6 in general. I switched then to the J/J KT77s. Fantastic! Yes, louder, but the character of the gtr tone was greatly improved. I also tried the Philips 6L6GC tube here, the famous STR# version with double getters - again, fantastic! And frankly, this tube is so good that it sounds fantastic in virtually any amp so no surprises.
OK, that is all I tried in the Hammond OT for now. The downside in using the larger tube is that the 25 watt volume is now pretty lost. The amp is just louder with the bigger tubes.
OK, so on to the TS M27 OT. I think this is a pretty good OT so it doesn't surprise me that, biased at 40 ma, the J/J KT77s sound great here. The Philips 6L6STR sound even better oddly enough. The Siemens EL34s, not as good as the J/Js, the Mullard XF2s, not as good as the J/J KT77s either. But hold on, wait till you hear the J/J 6V6s in here! They sound great. In fact, they make me a believer in the J/J 6V6 again, and right when I was ready to toss them. Crazy, huh?
As to the Pacific iron, all I have ever heard with it is the Mullard XF2 and it sounds fantastic! Which is kinda weird when you think that I do not like the Mullard with the M27 TS OT. To my ear, the Mullard with the TS OT has way too much midrange. So much so that it blurs the teble and the bass information.
OK, that's all. I thought I would post this to see if anybody else has a combination that they think is a winner.
This is regarding the basic Express amp, 400 plate volts.