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(d)
In the switch positions 'lV' 10.lV
I
and'O.OlV
I
the rotor is disconnected from +5V
and connected instead to OV (chassis) via contact 1 on SA1F.
ATTENUATOR ASSEMBLY AND SWITCHI NG: 9012 and 9013
3.7
The instruments type 9012 and 9013 are fitted with a discrete component attenuator
of relatively simple design, providing input attenuation of either OdB or 20dB,
according
to
the setting of the slide switch on the front panel. The switching of the
attenuator is by switch contact closure and no relays are employed. No provision is made
for remote control selection. The attenuator circuit and switching are shown in Fig. 4.12.
AMPLlFI ER DIVIDER ASSEMBLY: 19-0630
(Fig. 4.10)
Input Amplifier
3.8
The signal from the Attenuator Assembly enters the Amplifier Divider Assembly at
SKTl, with an input impedance of 50n and is applied to the amplifier formed by
transistors Ql, Q2, Q3 and Q4, which has a nominal overall voltage gain of 14. Adjust-
ment is provided at C3 and C8 for high-frequency compensation to ensure adequate gain
over the entire frequency range of the instrument.
Shaping
3.9
From the amplifier output at Q4 signals are fed to the shaper circuit consisting of
transistor Q6 and tunnel diode 02. When fitting a new tunnel diode to the p.c.b.
it is essential that the correct procedure is followed (see Chapter 4, paragraph 4.14).
The bias on Q6 is set by transistor Q5 with preset adjustment by R24. The signal across 02
is fed to Q7, and after further amplification, into the divide-by-ten integrated circuit
package ICl. The divided output is amplified by Q8 and applied
to
Q9 and Ql0. The
output from these two emitter-followers providing the dual-channel' drive
to
the Divider
Buffer Assembly.
DIVIDER BUFFER ASSEMBLY: 19-0506
Divide-by-100 Channel
(Fig. 4.7)
3.10
The input is received at pin 5 from th: emitter follower Q10 in the Amplifier
Divider Assembly and applied to the J and K inputs of the J-K bistable IC1, which
provides djvision by two. The out put from ICl is differentiated by C7 and R3 and the
resul tant pulse is amplified by Ql and Q2, provided that the NOR gate formed by Ql and
Q9 is open. If there is no connection to pin 7, the base of Q9 is at '0' level and Q9 is
non-conducting, but when the optional program facil ity
is
fitted, an inhibit level (111 state)
is applied via pin 7 whenever the "';' 10" output is selected at the remote programming
station. This III state turns on Q9, thereby inhibiting the';' 100 output.
3-3
9010-9013
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