I had a hum issue on my MR JTM45 reissue which I converted to Metro board and slightly modded to JTM50 (EL34 with marstran 128 OT) specs.
Now fixed, but it might be interesting for some of you who maybe have some similar problems.
The reference showed to ground the V1 cathodes on the ground lug of the 2nd filter cap can (on the RI located under the board).
I had to move the grounding of the filter cap with a long wire to the ground lug of the 1st filter cap (located between recto and output-tubes) and to move the grounding of V1 cathode to the buss wire at the first pot.
Now the amp is dead-quiet even when dimed
