Key Features
The B77’s reputation rests in large part on the quality and robustness of its mechanical engineering. The chassis is a die-cast aluminium structure, with the motor housings, head block, pinch roller arm, side bearers, and crossmember all cast rather than fabricated from sheet metal — a construction philosophy borrowed directly from Studer’s professional studio products and one that provides the dimensional stability essential for precise, long-term tape guidance. The three motors — capstan, and two reel motors — are all direct-drive AC asynchronous types, chosen for their simplicity and long-term reliability. The capstan motor is electronically controlled by a servo system that reads pulses generated by a precision-machined tachometer ring on the motor shaft and compares their rate against a stable internal oscillator, correcting any deviation immediately. The capstan shaft itself is machined to an accuracy of one-thousandth of a millimetre, hard chrome-plated, and artificially aged during manufacture to ensure long-term dimensional stability. The result is a level of speed stability — and hence freedom from wow and flutter — that was exceptional for a domestic machine and remains competitive today.
The head complement is three separate heads: erase, record, and playback, each optimised exclusively for its own function rather than sharing duties as in a two-head design. The record and playback heads are wound from Revox’s proprietary Revodur alloy — a physically hard, magnetically soft material developed for Studer’s professional multi-track heads, where wear resistance and electromagnetic efficiency are equally critical. Separate record and playback heads also allow the monitoring of what has just been recorded — off-tape monitoring — by switching the monitor circuit from the input signal to the playback head, something a two-head design cannot do and an important capability for serious recording use. The head nest includes provision for a fourth head position, which on some B77 variants accommodated a synchronisation head for audio-visual applications.
At 15ips, the half-track B77 delivers a frequency response of 30Hz–22kHz (+2/−3dB) with signal-to-noise ratio of better than 68dB — figures that compare very favourably with the best cassette decks of the period and place the machine firmly in the territory of professional archive and mastering practice rather than domestic convenience recording. At 7½ips the response is 30Hz–20kHz (+2/−3dB), still comfortably beyond the audible range. Distortion at 0VU is below 0.6% at 7½ips and below 0.3% at 15ips. The half-track format uses two tracks across the full width of the tape rather than four, giving each channel a significantly wider track and a correspondingly better signal-to-noise ratio than the quarter-track configuration — the trade-off being that the tape cannot be turned over and played in the opposite direction.
The front panel provides balanced independent record level controls for left and right channels, with monitoring switches that allow source or tape monitoring through the headphone output. Inputs cover low-impedance and high-impedance microphone, radio, and auxiliary line-level connections. Outputs are provided for amplifier connection, radio/tape, and headphones. The large backlit VU meters for left and right channels are supplemented by LED peak level indicators. A tape size switch selects between NAB and CCIR hub configurations. The built-in splicing block and non-magnetic cutter on the front panel panel facilitate tape editing directly on the machine. A fast-wind monitoring function activates the playback amplifiers during fast forward and rewind, allowing quick location of edit points by ear.
The MKI is distinguished from the MKII by the absence of a built-in vari-speed control — the MKII introduced this feature, along with revised audio and drive electronics.
Important Owner’s Notes
The electrolytic capacitors in this machine are original and have not been replaced. Given that the B77 MKI was produced between 1977 and 1980, the capacitors are now in the region of 45–48 years old and are well beyond any recommended service interval for components of this type. The machine is currently fully functional and has been mechanically serviced, aligned, and calibrated, but buyers should be aware that capacitor replacement is advisable as a precautionary measure and should budget accordingly.
Buyers should also be aware that pre-recorded open-reel tapes in the half-track format are considerably rarer and more expensive than quarter-track tapes. The half-track B77 is primarily suited to owners who wish to record their own tapes, or who have an existing collection of half-track recordings. Quarter-track commercial releases will not play back correctly on a half-track machine.
Technical Specifications (When New)
(Source: reeltoreel.de Revox B77 data sheet; cross-referenced with GB Audio B77 data sheet and Revox manufacturer’s product pages)
- Type: 3-motor, 3-head stereo reel-to-reel tape recorder
- Track Format: Half-track (2-track) stereo
- Tape Width: ¼ inch (6.25mm)
- Tape Speeds: 7½ips (19cm/s) and 15ips (38cm/s)
- Reel Size: Up to 10.5″ (NAB) with appropriate adaptors
- Heads: Erase, Record (Revodur alloy), Playback (Revodur alloy) — 3 separate heads
- Motors: 3 — direct-drive capstan (servo-controlled), direct-drive left reel, direct-drive right reel
- Frequency Response (15ips, half-track): 30Hz–22kHz (+2/−3dB)
- Frequency Response (7½ips, half-track): 30Hz–20kHz (+2/−3dB)
- Signal to Noise Ratio: >68dB (15ips, half-track, IEC weighted)
- Wow and Flutter: <0.04% WRMS (15ips)
- Total Harmonic Distortion: <0.3% at 0VU (15ips); <0.6% at 0VU (7½ips)
- Crosstalk: >45dB at 1kHz (stereo); >60dB (mono)
- Erase Ratio: >75dB at 7½ips
- Peak Recording Level: 514nWb/m (6dB above 0VU)
- Inputs: Mic Lo (0.15mV/2.2kΩ); Mic Hi (2.8mV/110kΩ); Radio (2.8mV/20kΩ); Aux (40mV/220kΩ)
- Outputs: Amplifier (1.55V/390Ω); Radio (1.55V/4.7kΩ); Headphones (5.6V/220Ω)
- Level Metering: Dual VU meters with LED peak indicators
- Rewind Time: approximately 135 seconds for 3,600ft tape
- Year of Production: 1977–1980 (MKI)
- Country of Origin: Switzerland
Why Buy From Us
With over 40 years of experience in the Hi-Fi industry, we are well placed to assess and test equipment of this type. Every item we list is fully inspected and tested before sale — this machine was mechanically serviced, aligned, and calibrated by Andrew in our workshop.
When you buy from us you can expect:
- Full inspection and testing prior to listing — not simply a visual check
- A 3-month guarantee on every item we sell
- Transparent descriptions with no omissions
- Professional packaging to ensure safe delivery
- After-sales support available by phone or email should you have any questions
Please note that specialist packing arrangements will apply to this item owing to its size and weight.
Summary
A fully functional, mechanically serviced, and calibrated example of Revox’s B77 MKI in the half-track, high-speed (7½/15ips) configuration — the version of the B77 that delivers the highest audio performance and is best suited to serious recording use. The three-head, three-motor, die-cast chassis design remains a benchmark of mechanical engineering for a domestic reel-to-reel machine. Prospective buyers should note that the capacitors are original and a recap is advisable; that half-track pre-recorded tapes are relatively scarce; and that NAB hub adaptors will be required for use with 10.5″ reels, as none are included. The asking price reflects the service work carried out and the capacitor status. This is a single-unit listing. Please feel free to get in touch with any questions prior to purchase.
