Monday, October 31, 2016

Extending the frequency range of Pioneer TX-7700 tuner

TX-7700 is AM/FM stereo tuner manufactured by Pioneer in around 1975 - 1980. This is basic tuner system which is specifically designed for "rack style" stereo systems. Compare with other tuner systems this tuner is not very popular and very limited information are available in the internet about this model.

This tuner is mainly build around HA1138 AM radio receiver, HA1156 stereo decoder and PA3001 (HA11225) FM IF amplifier IC.

The TX-7700 which I got is manufactured for Japan and because of that it is designed to work with 100V AC and frequency range is limited to 76MHz to 90MHz. In this quick post we demonstrate how to tune this stereo receiver to 88MHz to 108MHz by without modifying the circuit(s) of tuner.

In this tuner the main component which need to adjust is 5 turn inductor located in FM front end circuit (refer A in below photograph). The frequency range of the tuner can be adjusted by changing the spacings of this inductor. If tuning is getting difficult, slightly adjust the trimmer capacitor in that module (marked as B in same photograph).

FM front end components to adjust.

After carefully adjusting the inductor and trimmer capacitor we were able to tune TX-7700 into 88MHz -108MHz frequency range. Once the receiver is desired frequency range the clarity of the reception can adjust by tuning the compression trimmers located in tuning capacitor (refer C and D in below photograph).

Trimmer capacitors of FM tuner stage.

This method can be used to tune any analog (FM) tuner which have identical design to TX-7700.