A Quad II in for repair. Fault was Anode glowing in one of the KT66s. I removed the bottom cover to fault find and yes the coupling capacitor was leaking electrically feeding the control grid of the KT66. A very simple repair but do not forget that replacing the coupling capacitors will have an effect on the amplifier's performance because the old capacitors have a metallic body and that is a capacitor to ground of about 27pF. Suitable modifications must be made to counter the loss of this capacitance.
Also there were a few resistors in the driver stage that had drifted away from their tolerance and must be replaced.
Both amplifiers were repaired in the same way as I do not want the customer to come back in a few months with the same fault on the other amplifier of the same vintage. They have consecutive serial numbers and were last repaired in 1981.
Also there were a few resistors in the driver stage that had drifted away from their tolerance and must be replaced.
Both amplifiers were repaired in the same way as I do not want the customer to come back in a few months with the same fault on the other amplifier of the same vintage. They have consecutive serial numbers and were last repaired in 1981.
Before repair with faulty components.
After repair and new components fitted using the capacitor clamps to keep the repair sympathetic with the original build.
