Gramdeck x

Additional Info

From Tape Recording Magazine, April 1959

USING TURNTABLE TO DRIVE AN EXTRA TAPE DECK
Equipment under review: “Gramdeck” tape recorder.
Distributors: Pullin Optical Co. Ltd., 93-97, New Cavendish Street, London, W. 1.
Prices: Gramdeck £7 10s.; Control unit £5 12s. 6d,
The Gramdeck is a simple tape transport mechanism which, as the name implies, obtains its drive from an ordinary gramophone turntable. With the Gramdeck it is possible to record and playback tapes using only a normal. radio or record player in conjunction with the Gramdeck Control unit. The tape speed is arranged for 7½ inches at a turntable speed of 78 r.p.m.
The wow and flutter content varies slightly from model to model and is generally higher than is expected from the average domestic tape recorder. A transcription table naturally provides the best form of drive, although any modern record playing unit is suitable. By using a clockwork turntable a very economical portable recorder is made, which is ideal for use out of doors.
Setting up procedure is explained in detail in the eight-page leaflet supplied. To arrest the rotation of the deck itself there is an anchoring pillar which is screwed to the base plate or motor board. The deck must not bind on this anchoring pillar so that free movement of the deck plate is possible; otherwise a variation in pitch will occur once per revolution of the turntable. Spools of up to 7 inches in diameter can be used according to the amount of room available inside the cabinet. The single record/playback head can be rotated in its mount for azimuth adjustment. Since it has been accurately set on a pre-recorded tape it should only require adjusting when fitting a new head, and then with a test tape of 6k or 7k/cycles. Permanent magnet erasure is used, and the magnet has a guard which holds the tape clear to prevent accidents when playing back. One has to remember that there are no brakes on the spools, so that layers of tape are inclined to spill when lacing up. The take-up was inclined lo be slack on the test model, and a full reel of tape needed watching when approaching the end of a run.
The Control unit can be mounted flush with the outside of the cabinet or left as a free-standing unit. It is transistorised, and self-contained with its own dry cell. The current drain is only 2mA and the 9 volt battery will last about 600 hours. Connections have to be made to the amplifier pick-up and loudspeaker sockets, and the loudspeaker can remain connected to provide a monitor.
There are two co-axial sockets on the front panel for the microphone input and the record head on the Gramdeck. When switched to RECORD one transistor operates as a bias oscillator, and the other as n microphone pre-amp, with an input impedance of about 500 ohms, Suitable microphones of the moving coil type can be supplied by Reslo, Grampian, Lustraphone and Vitavox. The Acos range of crystal microphones can be used but a l00k resistor must be wired in series, inside the co-axial plug.
When recording the control unit output is passed into the pick-up sockets of the amplifier. If the Gramdeck is required for portable use the output can be taken directly into the record head. There is a switch on the front panel which is set on MONITOR for the first condition and DIRECT for the second condition. A playback can be obtained from the unit by using a pair of high resistance phones. There is no form of volume indicator provided, and one can hardly be surprised in a unit of this price. After a little practice it should be possible to arrive at a convenient recording level merely by listening to the loud-speaker monitor.
When the unit is set for playing back, both transistors are connected in tandem as a voltage amplifier incorporating a tone control. The output is approximately .25 volt and follows the standard CCIR characteristic when the tape speed is 7½ inches. The gap width is .00025 in. and a fairly level response is obtained from the control unit output over a range of 80 to 10,000 cycles ± 3dB. If hum is encountered on playing back it may be caused by the turntable motor field picking up in the record head. In this case the deck should be rotated about its capstan until the hum is at its minimum. Then the fixing pillar can be finally screwed down. There is a rewind handle included in the kit,, although the turntable can be used for rewinding by changing over the spools.
For the home constructor who wishes to build his own control unit and preamp, there is a circuit diagram and all other necessary information in the leaflet provided with the deck. The circuit makes use of a double triode valve (type ECC83).
There is much to commend this tape deck as an extra unit to supplement one’s equipment. As already explained it can be used out of doors as a self-contained recorder, or to record from the radio or any other source.
JOHN ALDRED.