[morzh]

If your rect. voltage 280V and the plate voltage is 200V at the output tube, then you should see the B+ as 280V - Field coil dropout, and you said it was 229V, so if your plate V is 200V as it should be (you listed 23 tube as the only one with a wrong plate V) the primary of the output xfmr will be the difference between the B+ and the plate and should be 29V (give or take).

Now the secondary will measure 0V DC Always, and 0V AC if there is no signal present, as it is a transformer and it will not pass DC as you know.


Do this: touch the input grid of the 6B5 tube with a screwdriver or a piece of wire.
(I touch it with my bare hands but I do not recommend you do it if you are not comfortable doing these kinds of things). Best is, take your DMM or VoltOhmMeter, set it to Volts, leave one lead loose and use another to touch that Grid.

Will you hear 60Hz buzz? If yes, go back one tube (76, is it?) and do the same. See where it stops.