"n cook" bravely wrote to "All" (20 Jan 06 16:37:24)
--- on the heady topic of " Marshall 4140 Amp question"

nc From: "n cook"
nc Xref: core-easynews sci.electronics.repair:355957

nc Replaced that dual cap and runs cool and no hum after 10 minutes.
nc But after an hour a hum develops, intrusive but not as bad as before
nc and at the same time a serious glow forms on the zinc coloured
nc metalwork of one pair of the EL34s.
nc All 4 EL34s tested good , otherwise just 2 off 1.5K resistors to the
nc grids of each EL34, correct values cold.
nc The push and the pull from the preamp are AC coupled, leaking cap
nc here? Swap pairs of EL34s to see if the core glowing ones are in the
nc new position or the original position ?


You should have checked the coupling caps for leakage first.
If then it still glows it could be a bias problem on that pair.
Seems like you are well on the way to restoring the amp.

A*s*i*m*o*v