B&K ST 140, ST 140M, ST 202 User Manual

B & K Components, Ltd.

The following procedure is for setting the bias and DC in the B&K amplifiers. Read the complete
procedure first. These procedures should be performed by a qualified technician.

1. Plug the amplifier into a variac. Monitor the (-) negative rail of each channel by removing
the fuse and placing a current meter across the fuse clips.

2. Connect an 8 Ω load to each channel. Supply an input signal of 100 mV RMS @ 20 Khz.

3. Slowly turn the variac up to operating voltage while monitoring the rails for excessive
current draw. The meters should not read more than 400 mA DC. If one or both read

more than 400 mA, turn the bias pots (P2) to minimum and retry.

4. Set bias of the amplifier by adjusting the bias pot (P2) mounted on the solder side of the
board to achieve a reading of 200 mA on each channel for models ST 140, ST 140M,
ST 202, and ST 202+. The bias for the Pro 600, EX 442 and M 200 amplifiers is 250 mA.

Setting the bias higher than stated only causes the amplifier to run hotter and burn out

faster. It does nothing for the sound quality of the amplifier.

5. Set the DC out of the amplifier by monitoring across the outputs. Adjust the DC pot (P1)
for 0 VDC ± 5 mVDC.

Thank You,

B&K Components, Ltd.

Old Union Road • Buffalo, New York 14227 • Phone [phone] • Fax [phone]