288 Monaural Amplifier Rev 1.2 8
6. Cathode Fuse
Use only ¼ Amp Slow Blow Fuse.
This fuse is in series with V3 and V4
output tubes to protect the output transformers and other circuitry from a
shorted or bad tube. If blown, check performance of the output tubes before
replacing the fuse to prevent damage from a failed tube.
7. Bias Current
Meters These measure the cathode current in milliamps of each power tube (V3 and
V4, respectively). At idle, with no input signal, their value represents the power
tube bias or idle current.
8. Bias Adjustment Screwdriver-adjustable potentiometer that is used to set the bias of the power
tubes.
See Section 3.3 –Biasing.
9. Hum Balance Screwdriver-adjustable potentiometer that references the preamp tube
filaments above voltage ground to lower the AC filament noise. This is usually
set in the middle and requires no adjustment. However, if hum is discernable
through the speakers, try rotating the potentiometer clockwise and
counterclockwise from the center position to minimize it. If no change occurs,
the hum is being picked up by another source.
10. Speaker Outputs Used for connecting the speaker load to the amplifier and makes sure that
the selection matches the speaker’s impedance to avoid damage to the
amplifier.
See Section 1.2 –Setting the Load Impedance.
11. Input RCA line level input jack designed to accept audio signals from common
audio components.
See Section 1.4 –Input Setup.
