Sony TC-55

The TC-55 was a mono portable cassette recorder (cassette-corder) manufactured by the Sony Corporation in Japan in approximately 1973. It was also known as "The Sony Action-Corder", a product from Superscope, and retailed for $139.95. Here are some of its features and specifications.

• Built-in condenser microphone
• Automatic shut-off in playback and record modes
• SONY-MATIC recording system
• Dual differential-balanced flywheels for stable tape speed
• Pause switch for instantaneous tape stop
• Integrated printed circuit board
• Four-way power source operation
• Record/battery indicator
• Built-in 2-inch diameter speaker
• Music/speech record selector
• Microphone input socket
• Monitor output socket
• Dimensions 1 1/2 inches × 5 7/8 inches × 3 7/8 inches
• Mass: 1 lb 14 oz

Review

It was marketed as a compact cassette-corder of exceptional quality and a "travelling secretary" that one could take virtually anywhere. In many ways, it was a wonderful piece of mechanical and electronic engineering that was ahead of its time. As well as the outer casing that was all-metal, the tape transport mechanism (TTM) was metal too. The thick metal components including screws and rivets in the mechanism gave the impression that it was designed to be robust and last, however it was probably because they were limited by the manufacturing methods of the time to make something lighter.

Back in the early 70s, to have a tape recorder with automatic level control, and automatic shut-off was a huge achievement; however this was something that most manufacturers would have eventually been able to achieve. What makes this design stand out is the use of dual differentially balanced flywheels to maintain stable tape speed. The application of this meant that they were looking for a design that could work in virtually any environment and they went to a lot of trouble to achieve this. Consequently this unit has two drive belts for the tape transport mechanism, and two more for the counter mechanism.

The electronic circuitry consists of 13-transistors, and one FET for the microphone input, and the unit could record continuously for 3-hours with a fully charged BP-23 battery pack. This unit has much in common with the TC-40, with a similar layout of tape controls at the top, and a removable battery compartment. Even the mechanical engineering is similar with dual flywheels, dual belts, and a large long motor horizontally situated to save space. One of the main differences with this unit is the pushbutton control mechanism providing cue facility. However the electronic engineering is very different as the TC-40 had an integrated circuit and discrete transistors, whilst this unit is completely transistor based. Its circuitry is based mainly around C634A transistor, which was a very popular general-purpose silicon device; however I also spotted some C632A, B324, 2SD72, and C1364 transistors. You can expect audio power output of 350 mW from a new unit in perfectly good mint condition. However a well used unit may not be as loud due to component degradation, and may require capacitor and transistor replacement.

Service Tips

Upon first sight, gaining access to the drive belts seemed daunting due to all the wires hand soldered and taped on the PCB. However, in the end I had to disconnect one black wire soldered to the motor body, and one pair of speaker wires, and I was able to flip the whole board over.

Whilst the secondary belt path is easy to note, the primary drive belt path can seem complicated as the motor pulley and the flywheels are on different planes. The main drive belt goes from the motor pulley (upper side) loops around the grey-coloured flywheel returning through the centre of the two flywheels touching a small arc around the brass-coloured flywheel and back to the motor pulley (lower side).

When reassembling, pay special attention to the condenser microphone wires as they may get into the pushbutton mechanism and prevent the play button from operating. When fitting the PCB back, make sure the record/playback switch on the PCB engages with the linkage in the TTM, otherwise you may find you are not getting any sound in play mode because the switch will be stuck in record mode.

The long counter belt is simple to replace and one simply has to remove a small part of the mechanism affixed with screws to gain access to the driver pulley underneath. However the shorter drive belt has wires going through the centre, which would have been soldered after the belt was installed. This of course complicates matters; however, luckily I did not have to change that belt.

Value/eBay

These units sometimes come up for sale and they can be in various states of condition from perfectly operational to totally non operational. One thing to note is that a broken unit will need servicing and that can take huge amount of time as these units were not designed for easy service. The drive belts and other perishables will be well past their useful service life so you will have your job cut out looking for rubber tyres and cogwheel parts. Even if the drive belts are not worn, it may have a kink caused by long-term storage and non use, and this may result in wobbly speed and sound. Hence, a broken unit on its own is not worth much, however a unit in mint condition in its original packaging with the cover and accessories is highly collectable. In recent years their prices have been skyrocketing due to its similarity with the TC-50, which was used on NASA Apolo missions.

The following pages of this multi-page article shows the inside electronic and mechanical engineering.

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