In rec.antiques.radio+phono Steve wrote:
We've all had experience with radios that refuse to work
properly. The latest one for me has been an HT-44 transmitter.
Been driving me nuts.
Finally discovered why. Hallicrappers decided to use steel
rivets to attach the tube sockets and terminal strips to their
aluminum chassis. To their credit, they
did put star lock washers between the bodies of the sockets
and the chassis, but over time, the rivets corroded and
are giving a poor ground. Time to dig out the bus wire.
I'm sure other manufacturers did the same thing. An issue
thats worth keeping in mind when working on them.

Not only on radio's... I own an Alfa Romeo 33 car, with an all-aluminium
boxer engine. Guess how bad the grounding of the alternator gets after
some years? I sanded down all contact surfaces and placed such washers
where possible. I should have added a jumper wire, but i didn't have the
correct materials handy at the time.

--
Met vriendelijke groet,

Maarten Bakker.