Grundig TK-18
A £40 19s. reel-to-reel that won't let you touch the recording level.
Overview
Grundig built the TK-18 around one stubborn idea: take the recording-level control away from the user and give it to a circuit. There is no magic eye, no meter, no knob. Automatic gain control in the recording amplifier - Grundig's "Magic Ear" - holds the signal reaching the tape at the optimum level. One contemporary reviewer said it is "virtually impossible to make a really dud recording" provided the input is above a certain minimum level. He wrote in The Tape Recorder (August 1963, p.40) that it felt strange at first to record with nothing to watch and nothing to adjust, but the results convinced him the AVC could cope with almost any eventuality.
The deck is a 3¾ i/s twin-track machine. Grundig's own specification quoted a frequency response of 40 c/s to 12,000 c/s within +3/−5 dB, and Studio Sound (March 1963, p.32) reproduced that figure directly from the manufacturer's list when the TK-18 was announced. Wow and flutter was rated at less than ±0.2 per cent, and signal-to-noise at better than 50 dB. Output power is 2.5 watts into the internal elliptical speaker. High-impedance and low-impedance outputs are on the back. The whole thing weighs approximately 20 lb and measures 14¼ × 11½ × 6¼ inches. Price, complete with microphone and tape, was £40 19s. from Grundig (Great Britain) Ltd. in Sydenham.
The "Magic Ear" is the reason to care about this deck, and it is not a simple compressor. Studio Sound (March 1963, p.32) described the mechanism in detail. The recording signal, after the frequency-correction network, is sampled, fed to a two-stage control amplifier, rectified, and returned as a control signal into the first two stages of the recording amplifier. The claim was that correct frequency response is maintained at all times with no increase in harmonic distortion. The circuit only engages once a very low signal threshold has been exceeded, which keeps background noise and hum from being pumped up during silence. There is also a memory system, with different storage durations for radio and microphone recording, so the gain does not chase every pause in speech.
That memory system is the part that divided opinion. The reviewer at The Tape Recorder (August 1963, p.40) found the AVC worked, but complained that the microphone and radio/pickup inputs were on the insensitive side. Few tuners or pickups deliver much above 0.3 V, he noted, so the AVC would only be called into operation on abnormally large inputs or when shouting an inch or two from the microphone. He had half expected a whisper at several yards to be lifted to the same level as a loud voice a few inches away. Instead it recorded like an ordinary machine set at about half gain, with the whisper down in the noise. Grundig's published reply, printed alongside the review, pointed out that the reviewer had not mentioned the different time delays built in to keep the level constant across alternating pianissimo and fortissimo passages. The delay network holds the correct level for long periods even when the signal amplitude drops.
Mechanically the TK-18 is a close relative of the TK-14, which the same reviewer had covered back in December 1961. A 1964 service article in Studio Sound (December 1964) treats belt-changing and brake adjustment for both machines in one go. The TK-18 differs in having an indicator lamp rather than a magic eye, since an automatic machine has no need for a level display. That article is also the best guide to ownership. It walks through removing the top cover (screws out, all six keys depressed, front lip lifted with the thumbs), the hidden screw under the pinch-wheel bracket, the two belts - flywheel-to-clutch and motor-to-flywheel - and the brake rods that should carry 1 mm of play in the neutral position. The right-hand brake is a plastic ring on a lug that engages the turntable periphery only when stopping after fast rewind. After fast forward, only the left brake acts. The clearance is tighter than on many machines, the writer conceded, but "quite foolproof in action when correct adjustments have been made."
One documented failure mode is worth knowing about. A 1967 service column in Studio Sound (July 1967) describes a TK-18 returned with "No Erase - Poor Record," traced to oscillator failure. The oscillator slug had slipped out of the "ridiculous little spring clip" meant to hold it and was sitting at the bottom of the former, held only by the tape over the adjustment hole. It looks like a dead oscillator and turns out to be a mechanical retention problem.
Studio Sound (December 1963) reported that the Royal National Institute for the Blind chose the TK-18 "Magic Ear" recorder for use by blind recordists, because the automatic level circuit abolished the need for visual tuning - up to then the main drawback for sightless users. The control keys were marked in Braille relief and the machine simplified as far as possible. The RNIB said no instruction book was needed. The first unit was presented at the London Hilton by Grundig's managing director to a representative of the Institute. The Braille version was available at no extra cost by individual order through Grundig retailers, at the same £40 19s. including microphone and tape.
The TK-18 sat in a crowded Grundig range and was not the flagship. When Grundig announced four new "L" models in 1965 - the Luxus TK 14L, TK 17L, TK 18L and TK 23L - the TK 18L was priced at £43 1s. against £38 17s. for the TK 14L, with the quarter-track TK 17L at £45 3s. and TK 23L at £51 9s. Those L-series machines moved to a smaller cabinet (13¼ × 10½ × 6¾ in., 22 lb) and quoted 40 c/s to 12 kc/s within ±4 dB. The original TK-18 also survived a round of Grundig price increases in early 1965 driven by the 15% import surcharge. Studio Sound (February 1965) listed rises across the TK.6, TK.40, TK.41 and TK.46 but noted the TK.14, TK.18 and TK.23A held their existing prices. By late 1965 Grundig's own advertising was pitching the TK18L at 41 guineas with the line about plugging in "humpots and fluttermeters" to test it.
The TK-18 is not a high-fidelity machine by the standards of its own catalog page. It is a 3¾ i/s half-track domestic recorder with 2.5 watts on tap, built for the household that wanted to capture speech and music without fuss. It is also a valve machine - EF86, EF83, ECC81, ECL86 and two metal rectifiers - that a patient owner can still service. Expect to replace belts, check the brake rods, and inspect that oscillator slug.
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