Sorry, no.My question is : As a test, can I just hook up the new output transformer without removing the old one, but just disconnect the speaker leads from the old transformer and use the speaker leads from the new temporary fitted one ? I realize I'm just being a bit lazy not disconnecting the existing transformer from the plates.
If as you report, the old OT suffers from weak low end, the reason is low primary inductance. Now if you parallel the 2 primaries, inductance will be even lower.
It would work in principle, though.