[radio1]

Experimenting with this radio, decided to bias the 47 tube's grid to -16.5 like the normal characteristic spec sheet calls for on the 47, was running around -20+ as is measuring with a Dynascan 177 Vtvm to ground. Took 4 meg ohm to bring it down to -16.5. Produced a most beautiful non-garbled sound especially with music and very pure heavy bass, but as in whack a mole, the hum suddenly increased, extra capacitance did not cure it.  Think it is ac heater hum as the spec sheet on the 47 says the input resistance at the grid should not be over 50k - thinking it soaks out the hum - the high resistance leaves it nowhere to go. Philco used 240k to feed the grid with the negative bias, so did they bias the tube wrong? I am researching the input impedance meaning a what it affects. No grid stoppers on this one.