the walkie-talkies), I included it in the
schematic. However, I think there is
enough gain for the system to work
without the transformer.
The first stage is a “long tail pair”
which has wide bandwidth and low
distortion, but the voltage swing is
limited due to the necessity to bias
the bases. Q3 is an emitter-follower
driving the Q4 grounded base. The
signal at Q5 can swing nearly rail to
rail, but with some distortion.
The bias is highly dependent on
the transistor beta (hfe), so you will
need to tweak R16 to get between
4 and 4. 5 volts at the collector. Q2 is
an NPN which is not as common as
PNP in germanium; Q1 and Q2
should be complementary pairs.
AC128 (PNP and AC127 (NPN) have
been suggested for the output
transistors; you can find them on
eBay. In Figure 7, I wanted to
simulate the audio transformer, which
required some guesstimates. If
the high impedance side is rated
■ FIGURE 8.
--- C:\Program Files\LTC\S wCADIII\AUDIO AMP.asc ---
type in the circuit. If you use
germanium transistors, be sure to use
germanium diodes. NV