[ARC5] BC-453 B dynamotor hum

[J Mcvey]

Hello all,
Been tweaking this beacon receiver in preparation for the 600m event in November. Peaked the IF's , but the dial is off about 2khz or so.Is this going to be hard to calibrate/? Maybe I should leave it alone?  I 'm wondering if it's worth the trouble. This radio is running on the original 24 V config.
Also matching the the output for best results using a 70V audio line transformer which seemed to be a toss-up between the 0.625W and 1.25W taps on this unit.
Now the only thing that REALLY bugs me is the constant dynamotor tone in the audio it sounds like 120 to 200 hz ( its really loud when the gain is turned down). Whats the most likely culpret? I had already replaced the potted caps with modern ARC pots from the 60's (?) which have white plastic tops. They tested good with very low ESR so I assumed that these are probably ceramic inside. Was this an error?

Any suggestions before I start hunting and pecking?
BTW, this radio works extremely well with my 160 M dipole> I have stations all over the dial. Picked up WD2XSH/38 which is reputedly only running 0.25 W in NH and I'm in southern NY.It doesnt like the shorter ones as much which kind of surprised me because an airplane is just so long...Didn't they work all these ARC5 radios off of the same antenna?