Food for thought.....

Sometimes a T-8 signal that has power supply problems can be cured by
removing excess capacity from the power supply filter or by loading
the power supply down with a series resistor load (some 7.5 watt to
15 watt lamps at about 75 volts per lamp do wonders).

The excess capacity causes an overly-long time constant that sounds like a
long slow chirp when keyed.  You can load the power supply down with lamps
or resistors to reduce the time excursion change in B+ or you can remove
capacity from the filter so that the time constant is so quick that the
chirp time constant becomes more like soft keying.  I use this latter
technique on Hartleys and it works great.  Somewhere between 4ufd and
8ufd works best in my hands.  You play a game with trying to reduce the
AC hum modulation vs trying to reduce the chirp time constant.

73/ZUT DE NA4G/Bob UP