Fairchild Model 248 Stereo Preamplifier-Equalizer (1958)
Two mono preamps, one master panel, and a half-inch slab of anodized aluminum - stereo's first serious console, styled by Raymond Loewy's office.
Overview
The Model 248 isn't a single preamplifier. It's a system in one case. Fairchild built it from two Model 245 self-powered preamplifier-equalizers and a Model 247 Stereo Control, all mounted together in one wraparound enclosure. Each 245 can run on its own, so a 248 could feed a single-channel system, a two-way or bi-amplified setup, or true two-channel stereo, depending on how the pieces are deployed. When Audio (April 1958, p.52) announced the unit as a new product, it described exactly this modular arrangement - two 245s plus a master panel in a single housing.
The cosmetics were not an afterthought. The cover is a half-inch slab of solid aluminum, anodized to a permanent black. The face panels came in white, aqua, or cocoa, with orange borders where the illumination diffuses across the control sections. The colored panels could be swapped at any time, which the contemporary review framed as a seasonal variation to suit the household's taste. Round knobs handle selector and volume. The tone controls are short bar knobs positioned so their settings read at a glance from across the room.
Inside each 245, the signal path runs through two low-noise EF86 pentodes, a selector switch, an interconnection socket, the tone controls, and both halves of an ECC83 in cascade. A 6X4 rectifier tube supplies plate power. A selenium rectifier furnishes 12 volts DC for the heaters of the three amplifier tubes, and DC on the filaments is one of the reasons the unit runs as quietly as it does. The 7-circuit selector switch handles low-level input selection, equalization, source selection, and grounding of unused inputs in one sweep. Inputs cover changer, transcription turntable, tape head, tuner, and auxiliary. There are two paralleled outputs for normal use, plus a separate tape-recorder feed taken ahead of the volume and tone controls.
The equalization was unusually thorough for the day. In the CHANGER position the 245 applies RIAA with a rumble filter down about 12 dB at 50 cps. The PHONO position, intended for a transcription turntable, offers three curves - RIAA, POP, and FLAT - with turnover at 500 cps for RIAA and FLAT and 800 cps for POP, the POP high end sitting between flat and RIAA. Tape-head equalization turns over at about 2500 cps for 7½ and 15 ips and about 700 cps for 3¾ ips. Input sensitivity is 1 mV for phono and tape and 0.18 volts for tuner and auxiliary, all for a 1-volt output. Tone controls provide ±12 dB at 20,000 cps and ±14 dB at 30 cps.
The noise figures were the numbers that counted. Fairchild's own literature claimed a usable signal-to-noise ratio better than 70 dB with average magnetic pickups and better than 80 dB from high-level inputs, and distortion of 0.1 percent at 1.0 volt output. The review even suspected the two 245 sections in its sample had been hand-picked, so closely did their equalization curves match.
The Model 247 control panel is simple. It has a four-position switch labeled STEREO LOUDNESS, STEREO FLAT, MONAURAL FLAT, and MONAURAL LOUDNESS, plus a volume-loudness control that doubles as the power switch. In the FLAT positions the equalization networks are shorted out. In the MONAURAL positions both channels are tied together. It does not provide right-to-left reversal, an omission the contemporary reviewer could not bring himself to regret. Two short cables connect the 247 to the sockets on the two 245s, and the panel carries a power cord, a power switch, and two power outlets.
Fairchild sweated the small stuff. Unused low-level jacks got shorting plugs to prevent the "open circuit" hum or noise that can appear as a switch passes an unused position. Every switch has bleed resistors so there is never a click when turning, which saves wear on the ear and on tweeters. High-Fidelity (December 1958, p.140) measured response from 20 to 20,000 cps at +2, −6 dB referred to the 1,000-cps level, looser than the rated ±1 dB limits. It also noted that switching the stereo attachment to MONAURAL drops each unit's gain by roughly 6 dB, producing an audible level change.
This one suits the collector who wants the physical object as much as the circuit. The half-inch anodized cover, the swappable colored panels, and the bar-knob tone controls make it a console component built like laboratory equipment. The modular 245/247 construction means survivors may turn up as complete 248s, as lone 245s, or as orphaned 247 panels. Buyers should verify that all the pieces are present and that the selenium rectifier and original tubes have been attended to. The DC-heater design is central to the low noise, so a unit that has been casually rebuilt may not measure as quietly as the review samples did.
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