DIY - Change capacitors

DIY - Change capacitors - Scott A436

DIY - Change capacitors - Scott A436


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.
Transistors Equivalent Transistors Equivalent
2SC733 BC182L/2N3710 2SC372 BC184L/BC237B
2SA495 BC214LB 2SC1000 BC184L/2N3707
2SA682 BD442/NTE374 2SC1382 BD139/2N5192
2SC793 BU123/2N5157 2SC793 BDY20/2N3055
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!

transistors Scott A436

Transistor and Diode Cross Reference
SERVICE MANUAL SCOTT A436

Free Download Service Manual


Change capacitors on Scott A436

Change capacitors on Scott A436

Change capacitors on Scott A436

Change capacitors on Scott A436

Change capacitors on Scott A436

Change capacitors on Scott A436

Change capacitors on Scott A436

Creating Loudness for Scott A436

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.