Does the 7A8 make noise on other higher frequencies when tapped gently? You may have a loose screen inside if it does. Try another tube. Are the connection good at all of the connections within the area of the tuning condensor? IS the voltage at the grids of the 7A8 within spec? or is voltage high? What is the conditon of caps marked on the Rdier schematic: 9,5, 6, and 22 in that order, are they open? Have the filter caps been replaced? If not, the filter cap in the B+ section, just after the field coil winding may be almost dried out too, and needs replacement.
The schematic here:
http://ww3.nostalgiaair.org/schematics/PHL/_PHL_12-43.gif
: I am trying to get a little Philco PT-2 bakelite radio going.From 1600 KC down to about 650 KC it runs just fine.At 650 KC it starts to oscillate (down to 550 KC) very badly..I have had no success playing with all (I think) by-pass capacitors or alignment.----Any help??---- Thanks,Olaf---Oh,HAPPY NEW YEAR-----