Greg has been very helpful. Turns out the resistors that go "puff" are on the underside, et voila one is burnt.
I may solder in a new one and carefully check how crazy the readings for V1 and V3 (V3's resistor went) turn out.
The current sets are KT120s from tubestore. I don't know how old.
As a next item a new matched pair V1/V3 may be the minimal step. Tempted to try getting a matched quad of 6550s and pair it with the existing quad of Shuguang 6550 As, although they have not received much applause in my other thread.
I may solder in a new one and carefully check how crazy the readings for V1 and V3 (V3's resistor went) turn out.
The current sets are KT120s from tubestore. I don't know how old.
As a next item a new matched pair V1/V3 may be the minimal step. Tempted to try getting a matched quad of 6550s and pair it with the existing quad of Shuguang 6550 As, although they have not received much applause in my other thread.