Quick description as per ICOM Manuals:
Quote
The AF amplifier circuit amplifies the detected signals to
drive a speaker. The AF circuit includes an AF mute circuit
for the squelch.
AF signals from IC1 (pin 9) are applied to the de-emphasis
circuit (R61, C89). The de-emphasis circuit is an integrated
circuit with frequency characteristic of –6 dB/octave.
The integrated signals pass through the high-pass filter (Q5,
R62–R67, C90, C91) to suppress unwanted lower noise signals.
The filtered signals are applied to the AF mute circuit (IC7B),
and then passes through the [VOLUME] control (VR board;
R1) via the “VOL1” signal. The signals are applied to the AF
power amplifier (IC6, pin 1). The output signal from IC6
(pin4) drives the internal (external) speaker.
Unquote
I thus assume the IC you are looking for is the IC described as IC 6.
Data sheet availible online:
http://www.datasheetcatalog.org/datasheet/sanyo/ds_pdf_e/LA4425A.pdf
The IC is a Sanyo LA4425A. A 5W Power amplifier.
