Heathkit S.33 integrated stereo amplifier
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Vintage test report


Taken from Amateur Tape Recording & Hi-Fi, March 1961

HEATHKITS, MANUFACTURED by Daystrom Ltd. of Gloucester, need little introduction, as they are well known throughout the world. Few people however realise how simple it is to construct equipment from kits such as these, for no technical knowledge is required and the only tools really necessary are a soldering iron, a screwdriver and a pair of pliers with side cutters.

The S.33 Stereo Amplifier kit comes complete with one of the finest instruction books I have seen. It is almost impossible to go wrong with 32 pages of well written and profusely illustrated text, plus nine large, stage by stage wiring and assembly diagrams. The instruction book provides the constructor with everything he needs to know, from the first stage of assembly to actual usage. The book includes notes on correct stereo operation and every component, nut and screw belonging to the kit is clearly identified by illustration.

The assembly and wiring of the S.33 is greatly simplified by a printed circuit board and the finished amplifier is quite equal in appearance and performance to any factory built amplifier of equivalent design. The cost: about half that of the ready-made product.

The S.33 comprises two high-quality integrated amplifiers in one case. It can be fitted into a cabinet or placed on a table or shelf and is finished stove enameled grey, with colour matched controls. Each channel provides 3 watts of power for stereo operation or 6 watts when the two channels are paralleled for monaural operation. Controls comprise ganged volume, ganged treble and bass, selector for gram or radio, mono/stereo switch, reverse stereo switch and a balance control. The specification is as follows:

Distortion: 0.3 % at 2.5w
Frequency Response: 30-20,000 ±2 dB
Sensitivity: 200mV
Negative Feedback: 20 dB
Stability Factor: better than 10 dB
Channel Separation: better than 45 dB
Hum and Noise: better than -60 dB (ref. 3 watts)
Output Impedance: 3 and 15 ohms
Valves: 2-ECF80, 2-EL84, 1-EZ81.
Power Supply: 110-125 and 200-250 AC, 40-60 cps.
Dimensions: 11 in. x 6½ in. x 4¾ in. (panel 11¾ in. x 5¼ in.).

The S.33 caters for stereo or monaural inputs from gram, radio or tape recorder. It is suitable for crystal, ceramic and high output magnetic pick-ups and has an input impedance of 1M.ohm. A built-in rumble filter takes care of turntable vibration.

Much more could be said about this versatile amplifier kit, if space permitted. Interested readers can obtain full and illustrated information by writing to Daystrom for the leaflets concerning this amplifier and the many other kits they produce.

Constructing a Heathkit is a pleasure; operating something you have produced yourself provides a lot of satisfaction. There is nothing difficult about building from kits such as the S.33 and in this case the end product is a high quality stereo amplifier that will do full justice to record, radio or tape reproduction. It performs to its specification and delivers some very nice stereo, providing of course it is used with good quality loudspeakers and ancillary equipment.

There is ample control over balance and Fig. 1 shows that the range of the bass and treble controls is more than sufficient to compensate for losses in pick-up, tape or radio signal sources.

The Heathkit S.33 stereo amplifier is manufactured and distributed by Daystrom Ltd., Gloucester. Price, complete with valves and full instructions for building is £11.8.0. Daystrom inform us that they will undertake to assemble, wire and test the amplifier ready for use for an additional cost of £3.15.0.