Quad AM2/3 service notes

Submitted by dada on Fri, 11/27/2020 - 14:00

1. Check all resistors attached to the HT line, including the screen resistor to the detector valve, and replace if more than 10% out of tolerance.

2. There are about ten film capacitors. If they are of the red Hunts type, replace them all on sight; otherwise measure and replace when out of tolerance.

3. Valves in these usually last forever: you are unlikely to have to replace them.

4. Carry out the audio-frequency alignment in the manual if you have appropriate equipment, changing the notch frequency to 9KHz as per international agreement in about 1978.

5. Check the 33R RF coil damping resistors and change if out of tolerance.

6. These units generally don't need much if anything in the way of alignment, and if they do it is best left to properly equipped and experienced tuner professionals.

7. In the AM3, replace the main PSU filter capacitor. This requires unbolting the transformer and carefully repositioning it by turning, so that the PCB can be removed to access the solder side. Note where all the screws, spacers, and nuts go. Reassembly of all this is quite entertaining.

Esmond Pitt

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