OK, so I am peaking the IF cans on the National NC-98 using a sig gen set to 455 kHz and the rig's S-meter for my indicator. When I finish, I disconnect the gen, but the S-meter stays high and there is no antenna connected. Uh-Oh, now when I tune through stations there is a hetrodyne (like the BFO is on, but it isn't). I have introduced an oscillation somehow, so I try to de-tune the IF's slightly. Both the received signal and the oscillation level drop. The S-meter indicates a signal all the time when no external signal is there. I need to start over from the beginning but the oscillation won't quit with the IF slugs in any position. I have traced it to the 2nd IF stage but all components check OK. Tried tube swap also. Voltages all in spec. Any ideas? Help!

Since detuning the if's changes the pitch of the whine,the problem is most likely not in the if stage itself. Did you align the oscillator section too? I would suspect the problem to be in the oscillator stage. But i dont have the schematic, so im doing general guessing here.

If your radios are anything like mine Walt,even with the signal generator disconnected and no antenna on the terminals,the radio can still pick up the generator.I usually tune the generator off frequency in between each stage of the alignment.My Rad- Shack dx-440 can pick up my S.G. easily from across the room with the antenna switched off.

Just a clarification; the sig gen was turned off and the oscillation remained, I am sure that it is being internally generated. De-tuning the IF cans only changes the amplitude of the signal and oscillation together (the S-meter drops). However the pitch of the hetrodyne remains the same. I call it an oscillation because the S-meter shows a presence of something when not tuned to any stations and no antenna is connected.

Don't know what type of IF cans you have there, but if it was working before you did any adjustments, it would seem a defect inside one of the cans. Hope it's not that silver mica thing in those K-trans type.
I have had a wire come loose from the adjustable cap when turning it before. Kind of did the same thing. would only howl and run amuck with oscillations.

:Don't know what type of IF cans you have there, but if it was working before you did any adjustments, it would seem a defect inside one of the cans. Hope it's not that silver mica thing in those K-trans type.
: I have had a wire come loose from the adjustable cap when turning it before. Kind of did the same thing. would only howl and run amuck with oscillations.

Have you switched off the beat oscillator?