METERED SLIDEBACK Position of Function Switch

22. METERED SLIDEBACK Position of

broken. The circuit action is identical with

that described for the CW PEAK position

Function Switch

(para 19c).

(fig. 12)

d. S702 Rear, Section W. The s w i t c h

Figure 12 shows that the METERED

wafer has been rotated 90 clockwise from

SLIDEBACK position of the function switch

its original CW AVERAGE position, which

disconnects the dc output at V702A cathode

results in two circuit actions:

( p i n 3) from the minus terminal of the

meter. Instead of indicating signal ampli-

(1) C o n t a c t is broken between termi-

tude, the meter now indicates that negative

n a l s 3 and 4. In the ZERO ADJ

voltage which is required to set the signal

p o s i t i o n , the full -150-volt output

level from audio detector V1 at the thresh-

of voltage regulator V709 was used

old of audibility. The various sections of

to block the signal path at the input

S702 accomplish this action as follows:

t o the if. amplifier (in the tuning

a. S702 Rear, Section X. The s w i t c h

u n i t ) . W i t h S702 rotated to the

w a f e r has been rotated 120 clockwise

PULSE PEAK position, this if.

from its original CW AVERAGE position.

a m p l i f i e r cutoff bias is reduced,

The long tab on the switch wafer creates a

and the normal bias voltage circuit

new path of continuity for the potential set

is restored (para 29a). Signal volt-

up across the SLIDEBACK control (in the

ages introduced into the if. ampli-

t u n i n g unit) between terminals 3 and 6.

f i e r are now amplified, detected,

S i m u l t a n e o u s l y , the dc signal path from

and coupled to meter cathode fol-

m e t e r multiplier resistors R723 and R724

lower V702 to produce an indica-

is open-circuited at the input to the meter,

tion on meter M701.

since terminal 4 of S702X has no path of

c o n t i n u i t y . Therefore, the negative termi-

(2) S i m u l t a n e o u s l y , contact is made

n a l of the meter is connected through rf

b e t w e e n terminals 4 and 5. The

filter FL702, dropping resistor R709, feed-

-150-volt output from voltage reg-

t h r o u g h capacitor C742, rf choke L702,

ulator V709 now has a path of con-

a n d contact 4 of receptacle J701 and its

t i n u i t y through dropping resistor

mating connector on the tuning unit, to the

R709, feedthrough capacitor C742,

negative voltage determined by the setting

and filter choke L702, to terminal

o f the variable arm of the SLIDEBACK

4 of main unit receptacle J701.

control.

With a tuning unit plugged into the

main unit, mating terminal 4 on the

b. S702 Front, Section Y. The s w i t c h

tuning unit connector applies a

w a f e r has been rotated 120 clockwise

p o r t i o n of the negative 150-volt

from its original CW AVERAGE position.

output as back bias to the plate of

F o r the first time in the circuit descrip-

audio detector V1, in the detector-

t i o n , contact is broken between terminals

e l e c t r o m e t e r circuit. The setting

1 and 2, and the dc return path to meter

of the front-panel SLIDEBACK con-

c a t h o d e follower V702 is effectively dis-

t r o l determines the specific bias

c o n n e c t e d . A new path of continuity has

v o l t a g e applied to the audio de-

b e e n created between terminals 2 and 6;

tector. Under this condition, back-

t h i s path places the positive terminal of

ground noise is removed and only

m e t e r M701 at chassis ground potential.

t h o s e peaks of the noise (broad-

Therefore, the meter indication shows

band) signals which are greater in

t h e amplitude of slideback bias (in db

a m p l i t u d e than the bias level set

a b o v e 1 microvolt/me) required to obtain

by the SLIDEBACK control are

t h e threshold level of audibility of a de-

m o n i t o r e d in headsets, when con-

t e c t e d signal.

n e c t e d to the main unit PHONES

jack.

c. S702 Front, Section Z. T h e s w i t c h