This is a design problem when receiving todays stations. When Radiola 18 was made stations were low power. Modern, high power, stations feed in, even without an antenna, to later stages of your radio. Grounding may help?
To reduce this effect I insert a metal plate under the amplifier portion of a radio. Bending the metal plate at right angles is even better shielding. I've also used copper clad PC board as a shield. Mount the shield between chassis and cabinet using two bolts which hold your amplifier.
Norm
:Hello
: I have recently restored an old model 18.I can not reduce the volume on very strong local station to an acceptable listening level.The original control seems to be working.The control is in the antenna circuit and controls the grid bias on the rf amplifier.The only way I can listen to very strong local staion is to de-tune the local station.