[BC] AM maintenance question

[Robert Paine]

 Do AM stations still routinely sign off Sunday night/Monday morning for transmitter maintenance? I recall hearing in the late 60's WABC going off for a few hours then coming on intermittently, sending various tones and doing other engineering-type stuff. 
 One night, sometime between spring 1968 and summer 1969, the station left the air for the usual work. As usual, they had the carrier off and on, after a while leaving it on for an extended period. One individual who had a sense of humor as warped as mine, opened the mic - the famous reverb working - and said, "From the echo chambers of the Blue Network Company" following with a laugh faintly resembling that of The Shadow", "hoo-hoo-hoo-hoo-hoo-hoo-haa- haa-haa!"
 For some reason I could never figure out, I never heard anything of the like again. I wonder why....

73, Bob KA3ZCI