[Heathkit] HW-16 problem

[Cam and Juli Hedrick]

Sensitivity is down, and I'm hearing an oscillation when I turn the AG gain
to off at 2 like a clock.  It happening when is warm, what cause this?  Boy,
new tubes in it as well.  Please help me guys.  I built this Hw-16 when I
was 13 years old.
73,
Cam Hedrick
WA4JKW