Western electric 23 a service manual

Page 1

Grid Bias Voltages

The following values of grid bias voltages are obtained by
using an external dc voltmeter having a range of 0-150 volts, 1000 ohms
per volt. Connect the negative teminal of the meter to ground and the
positive terminal to the circuit as indicated. Whenever a connection
of the meter is made, the plate voltage should be removed by operating
the "High Voltage" switch (DSA') to the "Off" position. The bias
voltages should be measured with normal output of the transmitter.

Modulating Amp. Unit

(Between Ground Tenn. & Slider of R48» 52 2t 2 volts
Modulating Amp. Unit

(Across MBA) '70 i 4 volts
3rd Amplifier

(Center Tap of MBA) 110 i: 5 volts

4th Amplifier
(Center Tap of 12211) 110 :t 5 volts

Should any of the bias voltages be incorrect when the plate
currents are correct, check the values of the resistances and make the
necessary adjustments. The values of the resistances are:

Apparatus _ Resistance
Designation Ohms
* RZGA ('Ibtal) 480 i 20
* RZSA (Fixed end to tap 16 :t 2
No. 1)
* R26A (Fixed and to tap 160 i 20
No. 2)
" R43A 500 :t lo
mas. (Total) 1000 :t 100
R48A (Gr. to Tap) 700 i: it"

*To measure these resistors first move both wires from
second slider from left hand and or R49.1 being careful
not to leave the wires connected together.

Page 2

Plate Voltages

The following dc voltages should be measured with an external
dc voltmeter having a range of 0-1500 volts and a resistance of 1000 ohms
per volt. At each measurement the "High Voltage" switch (BSA) shall be
"Off" whenever the meter is either connected or disconnected. and "On"
when the observation is made. The negative terminal of the meter shall
be grounded and the positive teminal shall be connected as indicated.

MW" 9.}
Dec illator .1
(Term. 2 on Dec. Tenn. Strip) 250 i 2 volts N/Jlnjflr, 7
let Rm. Amplifier (, 7M
(Term. No. 10 on Mod. Amp. Unit) 475 :1: so ' W1
3rd Amplifier 7 . 0,1,;
(Term. on rm) 1150 :t 100 " 4
Audio Amplifier
(Tenn. No. a) 475 i 50 " 4].; 77--
2nd R.F. Amplifier ,7 ,
(Term. R15A) 575 :t 25 " y "
4th Amplifier
(Term. No. 2 on L29A) 1360 :t 10 w it

Should the voltages be less or more than those indicated the
sliders on the plate voltage resistances R49.lA, 1149.311, R49.5A, and
1249.611 for the oscillator, second R.F. Amp.. 3rd RJ. Amp., and 4th
R.F. Amp. plate voltages, respectively, should be adjusted until the
proper voltages are obtained.