Teac A-7300RX

Teac took the A-7300, bolted in a dbx Type I encoder/decoder, and built one of the most flexible half-track decks of the late '70s.

Overview

The A-7300RX is a 1/2-track, two-channel stereo open-reel deck that takes both 10-1/2" and 7" reels. It runs at 15 ips (38 cm/sec) and 7-1/2 ips (19 cm/sec) with a speed tolerance of ±0.5%. Teac's own service documentation calls it "a high quality stereo tape deck representing a new Generation in the design and construction of recording equipment." It also says plainly that the basic design is "highly similar" to the earlier A-7300, so much of the A-7300RX service manual applies to its predecessor as well. The headline change is the built-in dbx Type I noise reduction, licensed from dbx, Incorporated.

The dbx system is the reason this deck exists as a separate model. Teac's manual points to the A-7300RX's "superior live recording capability" as the payoff, and pairs the dbx circuitry with an MPX filter, a CUE system, pitch control, and an edit function. The MPX filter strips the 19 kHz pilot from FM broadcasts before the signal hits the dbx encoder, which would otherwise try to track a tone that isn't program material. Owners who record off the air ignore that switch at their peril.

The transport mixes old and new approaches. A single DC direct-drive servo capstan motor handles tape speed, while two eddy-current induction motors drive the reels. Teac's service literature says the deck "uses highly reliable AC Motors for both reel motors, and a DC direct-drive capstan system," and that it "should require a minimum of mechanical maintenance or adjustment." Factory adjustments, in Teac's telling, should only be needed after long service or component replacement. The manual is also candid that the dbx encoder and decoder adjustments "are critical and should only be performed by skilled technicians."

The head complement is three heads - erase, record, and playback - which allows real-time monitoring off the tape during recording. Playback equalization is NAB at both speeds (50 µs and 3180 µs). The specs put wow and flutter at 0.05% WRMS in playback at 15 ips and 0.06% WRMS at 7-1/2 ips, with overall figures of 0.12% RMS and 0.15% RMS respectively. Those are honest numbers for a machine in this class.

Signal-to-noise is where the dbx earns its keep. Without noise reduction the deck is rated at 48 dB or higher. Engage the dbx Type I and the figure climbs to 60 dB or higher overall. Total harmonic distortion is rated at 0.8% or less with dbx at 1 kHz at normal operating level. Stereo channel separation is specified at 45 dB or more at 1 kHz, with crosstalk rejection of 35 dB or more on the adjacent track at 125 Hz. Erase efficiency is quoted at 65 dB or more at 1 kHz with input 10 dB above the specified level.

Line inputs are specified at -8 dB (308 mV) into 50 kΩ, with a minimum input of -18 dB (97 mV). Microphone inputs are far more sensitive, specified at -60 dB (0.774 mV) into 30 kΩ, with a minimum of -70 dB (0.244 mV). Outputs from the source/tape jacks are specified at -8 dB (308 mV) into 10 kΩ, with a maximum of -2 dB (615 mV), and the encoder output is specified at 8 dB (308 mV) into 50 kΩ. Headphone output is -24 dB (49 mV) into 8 ohms. Bias frequency is 100 kHz from a push-pull oscillator, ±5 kHz.

The deck is a two-box affair. The transport measures 470 × 455 × 300 mm and weighs 28 kg net. The amplifier section measures 470 × 205 × 310 mm and weighs 13 kg net. That's 41 kg of hardware before you add reels. Power requirements cover 100/117/220/240 VAC at 50/60 Hz, drawing 83W. Teac's parts list shows separate AC power cords stocked for general export and for Australia. The included accessories ran to input/output cords, a low-stray-capacity cord, a 12P plug and socket, a cleaning stick (TZ-275), splicing tape, a silicone cloth, an M3 and M4 hex wrench kit, reel adapter clamps (TZ-612) in pairs, and a 1A or 2A fuse depending on the variant.

The service data spells out the reel torque figures. Take-up torque is 530 to 570 g cm with the reel switch set to large and 330 to 370 g cm on small. Back tension runs 430 to 470 g cm on large and 280 to 320 g cm on small. Fast-forward torque is 1,900 g cm ±100 g cm, brake torque 2,200 g cm ±100 g cm, and the deck will wind a 1,800-foot tape end to end in 150 seconds. Pitch control offers ±5% or more, and counter accuracy is specified at ±1.5% at 15 ips in play mode. Pinch roller pressure is 1.8 to 2.2 kg.

The trade press covered the A-7300RX alongside the rest of the late-'70s tape machine field. A December 1977 survey of tape machines in Studio Sound (December 1977, p.48) listed it among the period's serious decks. It noted the full logic control and motion sensing, DC servo-controlled capstan, mic and line inputs, integral dbx noise reduction, and separate electronics and transport sections - the same split-chassis layout the owner's manual describes. The survey also flags remote control and varispeed as options, and memory linked to elapsed time, features that put the A-7300RX in company with the Tandberg machines of the same era rather than the budget open-reel decks.

The A-7300RX is a half-track machine, not a quarter-track. It plays and records two tracks in one direction, and it will not play the quarter-track tapes that most home open-reel libraries were built on. The dbx Type I system is also not Dolby B, and it is not compatible with Dolby-encoded tapes. A dbx-encoded tape needs a dbx decoder, and a Dolby tape needs Dolby. Mix them up and the result is unlistenable.

Maintenance is the other reality of ownership. The direct-drive capstan means no capstan belt to replace, but the pinch roller is rubber and decades old. Hardened or glazed rollers cause speed instability and poor tape contact. Tape heads accumulate oxide and need cleaning with isopropyl alcohol. They also need periodic demagnetizing, and misalignment shows up as phase problems and rolled-off highs. Teac's own service manual recommends a complete cleaning, demagnetization, and lubrication before any performance checks, and it warns that the dbx encoder and decoder trims should be left to skilled technicians.

What the A-7300RX offers, when it's running right, is the thing that draws people to open reel in the first place: a half-track, 15 ips recording with dbx noise reduction, three heads for real-time monitoring, and pitch control for matching sources. It's a machine built around the assumption that the owner wants to make recordings, not just play them back — and the dbx circuitry is the clearest expression of that intent. Teac put a professional-grade noise reduction system into a home deck and documented the whole thing in a service manual that's still circulating today. That documentation is half the reason these machines are still repairable, and it's a big part of why they still have a following.