[TenTec] Running a Century 21 on external 12V power

[Stuart Rohre]

There is an old radio troubleshooting trick:

You use a insulated test probe, (length of solid wire set in an 
insulated handle to safely handle it).

Move this to the plus end of each electrolytic cap, in turn, and see if 
the hum level jumps up.  Likely that cap may have dried out and changed 
to lesser value if you get more hum on one than others similar.

However, as this could be linked to the direct conversion receiver; add 
the RF bypass caps also, even one at a time, to see if the hum reduces.

Make sure no wiring has been moved around by earlier tinkerers.  (Maybe 
hard to determine on the point to point layout of early TT's.)

GL,
Stuart Rohre
K5KVH