Butoba clockwork tape recorders

Burger export

Wound-up machines?

In the 1950's, small speed-regulated DC motors were unusual, and so it was natural for a company that specialized in the manufacture of clocks and precision mechanics to start using clockwork motors for driving tape recorders. The motor used is principally identical to the type found in old record-players, however, there are a couple of differences. First of all, speed accuracy is much more important, as there is no audible means of checking the speed during record. Secondly, tapes play for much longer than the 3 or 5 minutes required to play a 78 rpm record. And finally, because of the lack of a turntable, there is no intrinsically large mass to filter out speed variations.

Drive unit view 1 Drive unit view 2
Two views of a Butoba spring drive unit. In the left picture, one of the two large mainspring canisters can be seen. In the right picture, the governor assembly is visible (with one of the three round weights mounted on its leaf spring facing directly into the camera).

Looking from another point of view, comparing the Butoba drive unit to the now conventional method of using an electric motor and flywheel to drive the tape, the Butoba motor stands out on a couple of points, apart from the spring drive:

All in all, the drive mechanism cannot have been cheap to manufacture, with lots of machined parts, especially considering the precision needed to minimize speed fluctuations. Not only the drive mechanism, but parts like the reel tables are machined and not stamped or moulded.

Rotating governor
The governor in operation: weights extended by centrifugal force, their rotating motion frozen by the camera flash

As a final note on the drive unit, it can be noted that not everything is driven by cogwheels, the exception being the take up reel clutch which is actually driven using a rubber belt.

Winding up

Winding up The crank for the motor is located on the underside of the machine, with the speed selector being located here as well. About 70 or 80 turns will wind up the springs completely.

Rewinding - and a sore thumb

The clockwork motor is only used for normal forward drive. There is no fast forward on these machines, and rewind is accomplished manually, by pressing a rewind button repeatedly, which via gears turns the supply reel. Unfortunately, during ordinary play, the rewind gears on the supply reel tend to rattle audibly, especially at the end of a reel at the higher speed. Rewinding

Pushbutton control

Export controls A Butoba hallmark is push-button operation. Although the rewind button cannot really be considered a push button in the ordinary sense, standard push buttons are used to control all other tape operations; two buttons being used for start and stop, and two other buttons being used for record/play selection. There is no record interlock; pressing record and then start immediately starts a recording.

The brown knob in the picture on the left is the reset knob for the running-time counter; the counter itself is visible in the little window above the knob. It was not present on the earliest models. The slot in the middle is the opening for the DM71 indicator tube.

Amplifier control panel

The amplifier controls and input/outputs are concentrated on a small recessed panel on the side of the machine. There are no markings on the panel. The left knob is the tone control, whereas the right knob controls the volume. Both knobs are active also when recording.

The three connectors on the panel are a type of thin jack connector that I've never seen anywhere else. From left to right they are line output, line input and microphone input. Early models had only this panel; on later models, as can be seen in the picture, an unusual male DIN connector is used for an external power supply connection. (I don't know what 'BNZ' stands for, but it sure sounds German). Later machines like the TS6 also have a couple of banana plug connectors for connecting headphones.

Volume and I/O

The "Export"

The 'Export'
The Butoba "Export"

The "Export" is an example of a typical Butoba spring-drive tape recorder with an all-tube amplifier. Not the first type to be produced (earlier models lack the running-time counter and external power supply input), I would guess it is from around 1955.

Export opened
Rear view with cover opened; drive unit on the left, amplifier unit on the right. The speaker below is covered in white cloth!

The amplifier uses 'battery tubes', i.e. with a filament voltage of 1.4V, and an anode (B+) voltage of 90 or 100V. When the recorder was built, such batteries were readily available for use in portable radios. Operating the machine today can be slightly problematic, as it's difficult to find a battery that delivers anything over 9V. However, current drain is low, and connecting ten standard 9V batteries in series results in 90 volts, and yields several hours of playing time. A standard "D" cell can be used for the filament battery. Interestingly, 9V batteries are mechanically very easy to connect in series as can be seen in the picture to the right.
Modern-day batteries
Using modern day batteries

15 Minutes

Simple as the mechanics are, the machine boasts two speeds, 7 1/2 and 3 3/4. At the higher speed a running time (per wind-up) of 15 minutes can be obtained, and a running-time-counter (the knob above the row of push buttons) is used to keep track of this. At the lower speed, twice that time can be achieved. However, speed regulation at this speed is not too good, the machine running a couple of per cent too fast just after wind-up, and slowing to a couple of per cent below rated speed when the running time has elapsed.

The main reason for the lack of speed regulation at the lower speed is that the governor is turning quite slowly at this speed, meaning that the weights are not extended very far on their springs, making the whole mechanism sensitive to friction and the amount of energy available from the mainsprings, which varies during the playing time.

Technical data

Not too exhaustive this, as I have no data sheet for the machine. The frequency response has been determined by measurement.

The TS61

Butoba TS61
The Butoba TS61

The TS61 was probably Butoba's last clockwork recorder. Externally, it looks virtually identical to the "Export" above. Internally, however, the chassis has been redesigned, and the machine uses transistors instead of tubes. In fact, apart from the output and driver transformers, the electronics are the same as in the later MT4 and MT5. The machine shown is from 1959, which is probably when the model was introduced.

Transistorized design

Still retaining the DM71 indicator tube for the record level, the TS61 uses an all-transistor design for the electronics, powered by four "D" cells. These should last a long time, as the current drain at low playback volumes is a mere 30mA. Most likely, this was the main reason to retain a clockwork machine in the range, i.e. the long playing time compared to a motorized design.

Slight redesign

Heavier governor weights, requiring slower speed to maintain regulation, a smaller capstan diameter, and most likely changes to the mainsprings as well, give this recorder a playing time (per wind-up) of 22 minutes or more, and the higher speed which is 3 3/4. At the lower speed of 1 7/8, 40 minutes can be obtained.

Compared to the "Export", the chassis has also been redesigned; this however turns out to be a bit of mixed blessing. While it is now possible to remove the drive unit without removing the whole chassis from the case, this must be done in order to replace the clutch drive belt, which on the "Export" is simply a matter of removing the upper capstan bearing.

An interesting side note is that the machine, like earlier models, was offered in several color schemes. Apart from the sombre two-tone grey vinyl depicted above, green or red crocodile could be chosen.

Technical data

User and Service Manuals

The user manual for the TS61 is, as for most equipment of that era, short, just a folded sheet of paper. It's available here as a two-page PDF file. If you want an authentic replica, make a double-sided printout, and fold in thirds along the two lines.
There's also a brochure available, again rather short, just a single fold this time, so four pages in total.
The service manual for the TS6 is available below, in German language. (The TS6 is essentially identical to the TS61, except that the electronics is built on tag boards rather than PCB's.) It includes descriptions, repair instructions, lubrication chart, spare parts list, schematics and numerous pictures.
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