I have a Grundig tube radio - 4070U - which I love dearly. I bought it
almost five years ago and had it restored by someone who knew what he
was doing. I no longer live in the same area and can't benefit from
his services again.

It has two problems. The right channel cuts out intermittently. The
sound can be restored in two ways: if I turn the volume way up, or
(sometimes) if I give it a rap on the case. In both situations, the
sound is restored with a small pop. In addition, the sound also
returns if I do nothing, i.e., if I wait a few minutes. But then of
course it disappears again.

The other problem is that the sound in the left channel is extremely
weak. It is possible to hear it if the right channel has cut out, so
something is arriving at the speaker, but not much. This one is not an
intermittent problem.

The restoration in 2001 included replacement of capacitors. Not sure
if it included replacement of tubes.

Any suggestions received with gratitude.