[morzh]

Here's what I've just tried - I plugged my 20 lowboy's speaker right into the 90, they are exactly the same compatible pliugs and, at least when original, the same speaker and the same transformer.

My 20 has re-coned speaker and hammond 125C-CT pushpull transformer whoe taps were chosen to closely match to what was used before, which should be close enough to both 71A and 45 tubes' requiremenrts.

Well, I hear very much the same distortion.
What's more, my 20 sounds very close to the 90, the distortions of the 20 (which I complained of before a while back) being very similar to 90's.
The 20 sound has way less bass but otherwise that choppinness during some sounds is the same in both the 20 and the 90. Which makes me think of the detector.

Which will not sway me from buying a proper transformer - I still want to hear the sound with correct loading of the push-pull.

PS. I just realized that I have another 20 delux cathedral which I have just bought recently.
But when I checked the speaker the field coil was open (though the transformer seems OK). I am not sure but somehow I think maybe the cone in that one is original also. Well, so much for this one.