Tandberg Model 64X
A bias head bolted onto an already-excellent deck, and suddenly 3¾ ips stopped sounding like 3¾ ips.
Overview
Tandberg's own advertising for the 64X called it "the world's best stereo tape deck" - and backed that up with a specific technical story. The company took its existing Model 64, added a dedicated bias head, and refined the circuitry. The result was a three-speed, four-track stereo deck that, at 7½ ips, was specified to reach 20-25,000 c/s with ±2 dB limits from 30 to 20,000 c/s. Those numbers made tape enthusiasts sit up in 1967, because they suggest a top end that extends well past what most listeners could hear.
The bias head is the center of the 64X story. It faces the uncoated side of the tape, opposite the recording head, and Tandberg credited it with the deck's improved frequency response and signal-to-noise ratio. The specified S/N figures were 62 dB at 7½ ips, 59 dB at 3¾ ips, and 56 dB at 1⅞ ips. Those were strong for the period, and the low-speed number is the one that mattered most. A deck that holds 59 dB at 3¾ ips can handle serious music recording without much hiss.
The rest of the package is a proper Tandberg. It has four separate tape heads, three speeds, sound-on-sound, echo effects, add-a-track, direct monitoring, and a centre-channel amplifier for simultaneous playback of two tracks into mono headphones. The oscillator circuit is fully transistorised, and the outputs are cathode-followers. The cabinet was teak and stove enamel. The deck measured 16 × 12 × 6½ inches.
Pricing in the period was $549 in the US, or 115 guineas in the UK for the two- or four-track Series 6X. That was serious money, roughly the price of a decent used car in some markets. Tandberg positioned the 64X accordingly, as a high-fidelity instrument rather than a consumer convenience.
The critical reception was strong. Hirsch-Houck Laboratories tested the 64X for Audio (August 1968, p.48), and their measured record-playback response at 7½ ips came in at +0.5, −2.5 dB from 40 to 20,000 Hz. That is close to the published spec and excellent by the standards of the day. The same lab had reviewed the original Model 64 back in October 1963 and found it unusually transparent. The 64X, in their assessment, improved on it, particularly at the lower tape speeds.
The original 64 was already a respected machine. The X added the bias head and the circuit refinements that let the deck deliver genuinely high-fidelity performance at 3¾ ips, a speed most competitors treated as a compromise.
The teak-and-enamel cabinet has held up well cosmetically. Tape decks of this vintage need belt and idler attention, and head wear is a real concern on a machine that was often used heavily. The hybrid tube/transistor electronics mean service requires someone who knows both. The 64X is not a beginner's project.
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