FM-3A FM Tuner
- Edge-lighted slide-rule dial for easy tuning
- Incorporates AGC, cascode front end, temperature-compensated oscillator for stability
- Efficient, modern circuit uses miniature tubes throughout
- Pre-aligned IF and ratio transformers—partially pre-assembled front end—easy to build
- Two outputs—one fixed, one variable, with extra stage of amplification
The Heathkit FM-3A Tuner is a time-proven unit that offers sensitivity, selectivity, and stability not expected at this price level, and will bring you a rich store of FM programming, your least expensive source of high fidelity material.
Its efficient, modern circuit uses 7 miniature tubes to provide better than 10 microvolts sensitivity for 20 db of quieting. A high-gain, cascode-type RF amplifier is used ahead of the tuner to increase overall gain and reduce oscillator leakage. A stage of audio amplification is also provided for more than adequate output, an added advantage since it allows operation with any amplifier system regardless of sensitivity. Two outputs are provided, one fixed and one variable so output can be controlled at the amplifier or at the tuner. Another fine feature is the ratio detector type output transformer which has the advantage of being self AM limiting, eliminating the need for two limiter stages., The limiting threshold encountered with discriminator type transformers does not have to be overcome, allowing it to pick up many more stations of listenable quality without distortion. For this reason the FM-3A although rated at only 10 microvolts sensitivity will outperform 2 and 3 microvolt tuners. Automatic gain control is provided and the oscillator circuit is stabilized through the use of special temperature-compensated condensers for positive lock-in characteristics. Steady no-drift operation after initial warmup. The tuner has its own built-in power supply and covers the entire FM band frequency range of 88 to 108 megacycles.
One of the outstanding features of the modem FM-3A is the ease with which it can be constructed, even by a beginner. The fact that the transformers are pre-aligned, and the front end unit partially pre-assembled and pre-aligned, means that stations may be tuned in as soon as the unit is completed. Then it can be "peaked up" to a received station as described in the manual for maximum sensitivity.
The wiring is accomplished by following check-off type step-by-step instructions and large, clear, pictorial diagrams. It is not necessary to read a schematic diagram. The manual even contains information on soldering techniques, tips for beginners on circuit wiring, information concerning required tools, etc. Your success is assured through Heathkit complete construction manuals.
An edge-lighted slide rule dial is provided for easy tuning, and the unit is housed in an attractive ventilated cabinet (included with the kit). It can also be mounted in a "custom" installation if desired. The FM-3A is an excellent performer using only high-quality components throughout. A worthwhile addition to any hi-fi system for years of outstanding performance.
Specifications—Tuning Range: 88-108 mc. IF Frequency: 10.7 mc. Antenna Input Impedance: 300 ohms. Output Impedance: Fixed output, 47K ohms; Variable output, 15K ohms. Output Voltage: (30% modulation at 100 uv input) Fixed output, 0.12 volts; Variable output, 1.5 volts. 20 db Quiteing Sensitivity: UNALIGNED—88 mc., 8 uv; 98 mc, 10 uv; 108 mc, 15 uv. ALIGNED—88 mc, 5 uv; 98 mc, 8 uv; 108 mc, 9 uv. Tube complement: 1-6X4 rectifier, 1-6BQ7A cascode-type RF amplifier, 1-6U8 oscillator-mixer, 2-6CB6 IF amplifier, 1-6AL5 ratio detector, 1-6C4 audio amplifier. Power requirements: 105-125 volts, 50-60 cycles, AC 35 watts. Dimensions Overall: 12 9/16" long x 3 5/8" high x 5 3/8" deep. Shipping Weight: 8 lbs.