Blonder-Tongue Audio Baton B-9 Tube Graphic Equalizer – 4U Rackmount, Pro Tech Ported – Rare Vintage

Rare Blonder-Tongue Audio Baton B-9 (1959) – the world's first commercial all-tube graphic equalizer.

9 octave bands (40 Hz to 10,240 Hz) with ±28 dB total control range (±14 dB boost/cut typical), piano keyboard reference chart on top, and iconic barber-pole visual feedback (rotary wheels move red stripes in slots for precise graphic EQ).

Legendary secret weapon of top engineers like Jack Joseph Puig for its silky tube magic for warm, musical, and characterful in a way modern EQs can't touch.

Professionally ported/modified into sturdy 4U rack by pro audio tech, and inputs/outputs redone to mono jack (1/4" TS unbalanced) for easier patching. 

Runs on 240V.

Tube complement: 5× 12AX7 (preamp/EQ stages) + rectifier. 

9 octave bands (40 Hz to 10 kHz), boost/cut per band.

Audio line level: original vintage hi-fi/consumer unbalanced RCA I/O – non-linear tube operation (sweet spot around -10 dBV to +4 dBu-ish; soft saturation/harmonics when driven for character). DI box, gain stage, or interface often recommended for clean +4 dBu balanced pro integration.

Fully working condition.

Super rare – most surviving units are original tabletop; this rack version is ready to drop in.