Classic UREI filter set traditionally seen in broadcast, film & archiving studios for noise & hum filtering. The 565 has sweepable high- and low-pass filters plus two boost / cut notch filters for cutting narrow-bandwidth notches in the audio spectrum. Each filter has a wide, narrow and T-shaped super-narrow notch setting. They’re the secret weapon of a number of engineers who use them to tame ringing snare drums…

These are rare items but I had three on the bench recently!

UREI 565 Filter Set