Wurlitzer 140B
The first solid-state Wurlitzer electric piano — brighter than the 200A that followed, and still running on just 30 watts.
Overview
The 140B is the model that finally cut the cord on tubes. Where the earlier 140 ran a germanium transistor complement and the 145 and 720 stayed firmly in vacuum-tube territory, the 140B moved to a mixed silicon-and-germanium transistor amplifier — and the whole instrument draws only 30 watts from a 117-volt, 60-hertz wall outlet, down from the 40 watts of the 140 and the 85 watts of the tube models. That's a genuinely modest appetite for an amplified, electromechanical piano, and it tells you something about how far the console electronics had come.
The tone-generating heart is unchanged from the rest of the family: 64 notes running from A-13 (55.000 C.P.S.) up to C-76 (2093.005 C.P.S.), produced by Sandvik Swedish steel reeds, electrolytically coated, that vibrate in an electrically polarized field when struck by the hammers. The reeds are the fixed-plate side of a capacitance pickup system, and the polarizing voltage sits in excess of 165 volts through a 10-megohm resistor — high enough to do the job, low enough that the manual is at pains to note it isn't a shock hazard. The hammers themselves are three-ply maple moldings with maple crossbanding, faced in white mothproofed felt with underfelt in the bass section, glued on with water-resistant adhesive. The naturals are white Implex over basswood; the sharps are black molded plastic.
The action is Wurlitzer's own 64-note design, and it behaves like a conventional piano action in miniature. Depressing a key sends motion through the whip and fly to the butt knuckle, driving the hammer toward the reed; about 1/8" out, the heel of the fly hits the regulating screw head and escapes, letting the hammer free-travel into the reed and rebound into the check. The damper lifts as the hammer starts its travel. It's a real mechanical action, not a switch under a key, and it's the reason these instruments feel the way they do.
The amplifier is where the 140B earns its place in the story. The reed-bar signal feeds an impedance-matching stage, gets amplified, and drives a push-pull output stage through a driver transformer that splits the signal into two equal, 180-degree-out-of-phase halves; the outputs are direct-coupled to the speaker. There's a phono input sharing the coupling cap into the second stage, a closed-circuit earphone jack that cuts the speaker for silent practice, and a vibrato circuit built around a low-frequency phase-shift oscillator. That oscillator's output is variably isolated by the vibrato control and fed through a capacitor and resistor to an incandescent lamp sitting alongside a light-dependent resistor inside a metal light-shielding enclosure. As the lamp flickers at the vibrato rate, the LDR's resistance swings, and because it sits in series with a capacitor across the second stage's emitter resistor, it varies the stage's gain — a variable emitter bypass doing the modulation. It's a lovely, entirely analog way to get tremolo, and it's the kind of circuit that makes old Wurlitzers worth opening up.
The 140B's speaker is a 6" x 9" oval permanent-magnet unit with an 8-ohm voice coil — a step up from the 4-ohm coil in the 140 and 145. The instrument also carries a 1/4" output alongside the internal speaker, which is part of why it turns up on records: engineers could take the direct signal or mic the box.
Mix (1994, p.315) singled out the 140B in a roundup of vintage keyboards being recreated in sample libraries, listing it alongside the Hohner D6 Clavinet and Celeste among the year's highlights.
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