12.8.3 Circuit Description
This differs from the Amplifier E only in minor details. As unity gain is
required in the present case, only a low value of resistor is required between the
collector of the VT2 and the emitter of VT1. In this case it is an adjust on test
component only. For testing the board this has a value of 620
Ω
but it is replaced by
the value required to provide the correct channel gain when the cassette is on test.
R1 is included to provide about 0.5dB of loss so that by selection of AOT1 a range
of gain on both sides of unity can be covered. The input base is held at –3.5V by
R3 and R4. Since this amplifier is used after an attenuator which is designed to
have a 50k
Ω
load, the input impedance has this value.
12.8.4 Output
The output is similar to that of the Amplifier E except that the G is designed to
deliver a minimum of 2.1V r.m.s. into a load of 3k
Ω
.
12.9 Amplifier Type G + B
12.9.1 Purpose
For convenience of cassette layout it is desirable to have a board with one
Amplifier G and one Amplifier B on it.
12.9.2 Circuit
The circuit diagram is shown on Drawing No. AE210. Apart from component
references the circuits are identical with those shown on Drawing Nos. AE209 and
AE204, so no further description is necessary. The small letters “g” and “b” denote
the inputs and the capital letters “G” and “B” denote the outputs of the Amplifiers G
and B respectively.
12.10 Amplifier Type H
12.10.1
Purpose
This is used in the studio loudspeaker channels in the Studio Playback
Cassette. It serves three purposes. Firstly it provides 10dB of gain to restore the
signal to standard level following the 10dB of loss introduced by the level control at
its normal setting. Secondly it provides two equal outputs in anti-phase so that, by
switching from one to the other, the signal can be poled. Thirdly it provides outputs
suitable for parallel connection so that both channels can be fed to one
loudspeaker.
12.10.2
Circuit
The circuit diagram is shown on Drawing No. AE211.
