DIY - Change capacitors
Purpose of the operation: Complete renewal of electrochemical capacitors. Adjusting the BIAS output transistors (quiescent). Cleaning the knobs and different contacts. Note: For marking of components on the PCB, they can be wrong. Do not overheat welding because the tracks tend to peel off.
Taking the measure of restoration before quiescent current. A photograph of the card. Use a marker to identify the polarity of the capacitors. Change capacitors one by one to avoid an error. Treat welds and pay close attention to the polarities. Before reconnection, do a check of the cards.
Adjusting the BIAS.Setting the quiescent currents (powers of the amplifier circuits). Do not apply signal to the input of the amplifier, volume 0. Output terminals of senior speakers: nothing connected. Use only a multimeter, and know the precautions and safety measures face a unit. The voltages in the device approaching 250 volts!
Left Channel:Adjust the variable resistor (R808) Check the voltage between (A and B), and set to 8 mV quiescent current.
Right Channel:Adjust the variable resistor (R833) Check the voltage between (A and B), and set to 8 mV quiescent current.
Results:A transformed amplifier, much more musical, more detailed. A great device, this Scott amplifier A 436. A vintage amp that I recommend!
Transistor and Diode Cross Reference
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More potentiometers with Loudness plug! Here is a trick to fix it: Resistance of a 1/2 W in series with the potentiometer (100 KB), on each channel, of course, the loudness function will be able to work, but at the expense of travel. A resistance of 100 k, but will increase the work stroke of significantly potentiometer. 50k is a better solution, to adjust to your taste also for more or less serious.