The Western Electric No. 100E Loud Speaker Set consists of an amplifier, associated power supply, and a loud speaker mounted in a small cabinet suitable for placing on a desk or table.


Circuit See Figure 2.
Amplifier Two-stage, employing heater type pentodes and a rectifier tube.
Gain 60 db maximum.
Output Power 0.378 watt (or +18 db level on the basis of a reference level of 0.006 watt) with' 10 per cent third harmonic.
  Note: For speech transmission this volume output should be satisfactory for groups of listeners of about 75 to 100 persons under favorable conditions.
Output Noise Level
(Energy basis is unweighted)
-20 db
Input Impedance
(Impedance from which the amplifier is designed to operate)
300 to 600 ohms.
Impedance at Amplifier Input Terminals
200 + j400
700 + j650
1000 + j600
Output Impedance The output transformer is furnished with the Loud Speaker (Voice coil d-c. resistance 5 ohms).
Frequency Characteristic Uniform within + 5 db from 300 to 3000 c.p.s.
Variable Gain Control Potentiometer (Control knob on left at front of cabinet) 45 db variation with practically uniform attenuation throughout 90 per cent of rotation with rapid increase in attenuation to cut-off.
Power Required. 105-125 volts d-c. or 20-65 cycles a-Co 60 watts maximum. (May be plugged into an ordinary electric light or similar socket.)
Width 11 1/2 inches.
Height. 7 1/2 inches.
Depth 5 1/2 inches.
Weight. Approximately 11 pounds.
Mounting. On desk or table.
Vacuum Tubes The vacuum tubes required for the operation of this amplifier are:
1-Raytheon-25Z5 &tab;(Rectifier) *
1-RCA-77 &tab;(First Stage) **
1-RCA-43 &tab;(Second Stage)
* Raytheon 2525 replaces former RCA 2525 designated V 3. Condensers designated C4 replaced by two 20 MF condensers.

* * If an RCA-77 type tube is furnished with this set, it is a selected tube and is satisfactory for use in this set. However, due to a change in the manufacture of this tube, the RCA-78 tube will replace the RCA-77 tube in future sets. The RCA-78 tube should, therefore, be used for all field replacements.

The tube sockets are mounted sub-flush to the top of the chassis so as to permit replacement of tubes without removal of the chassis from the case. The location of the large holes in each socket, which engage with the heavy prongs of the heater elements of the tubes, is marked on the chassis by a red rivet head.

The set is equipped with two high-insulation cords, one of which is terminad in a standard fixture plug for connection to the power circuit and the other in spade terminals for the input connection.


Connect the input cord (the cord with spade tips) to the source from which set is to operate. With the volume control knob and power switch set at maximum counter-clockwise positions, insert the power cord in the receptacle. In installing the No. 100E Loud Speaker Set, the power cord must be poled correctly when connected to a direct-current power source. Also, it is usually desirable to pole it for alternating-current power sources since the noise with polarity is generally less than with the other. When the proper polarity for ven installation is determined, it should be left unchanged.

The power switch (right-hand knob) has three positions. In the first, or off position (maximum counter-clockwise), the power supply is open. In the second position (intermediate) the power circuit is closed at reduced current and the signal lamp lights up with moderate brightness but the set is inoperative since the amplifier output is short-circuited. Also, the intermediate position provides sufficient current to maintain the tube heating elements at a temperature where response may be obtained quickly from the amplifier when desired without shortening the life of the tubes as would be the case if the heating current were left continually at full value. In the third position, full current is applied to the set and the brightness of the lamp indicates that the amplifier is ready for operation, the short being removed from the output. The time required for the tubes to heat to operating temperature after switching from intermediate to operating position is approximately five seconds.


No routine maintenance is required for the No. 100E Loud Speaker Set other than the replacement of vacuum tubes. If the set fails to operate, test the power supply and the associated polarity, particularly if the power supply is from a direct-current source. Should the signal lamp fail to operate (and is not it out) and the wiring of the heater circuit is found satisfactory, insert new tubes successively in their respective sockets to determine whether or not the heater element of any one tube has opened. Should the set still fail to operate properly, the apparatus and wiring should be checked piece by piece using as a guide the schematic circuit shown in Figure 2.

If it is impossible to locate the cause of the trouble and the customer desires to avail himself of the engineering services of the Western Electric Company, the matter should be taken up with the nearest distributor.

Instruction Bulletin No. 839