Western electric 129 a schematic

Page 1

Western Electric Company
No. | 29-A PRE-MIXING AMPLIFIER

Figure 24 - 129A PreAMixing Amplifier.

Use - The 129A is particularly designed for use as a pre-
mixing or booster amplifier in high quality AM and FM
speech input and sound systems; it can also be connected
for use as a group of "no-gain" low level bridging isolation
amplifiers.

Descriplion - Four identical two-stage amplifiers with
fixed gain, mounted on a common chassis, comprise the
129A unit. Four electrically separate audio channels are pro-
vided in which the inputs from four low level sources (mir
crophones or reproducers) are simultaneously and individ-
ually amplified prior to mixing, Each input transformer is
arranged so that it can be rotated to provide a minimum
pick-up from electromagnetic field interference. Cathode
resistors are provided to permit tube checks.

Features

High quality pre-mixing and booster amplifier.

Useful with no-gain low level bridging isolation ampli~
fiers.

Four electrically separate channels for simultaneous and
individual amplification.

Designed for minimum pick-up from elecrromagnetic
field interference.

Cathode resistors for tube check circuits.

Stabilized feedback.

Specifications

Frequency Response: Flat within :1 db over the range
50 to 15,000 cycles,

Output Noise: -82 dbm unweighted, -87 dbm weighted.
(Normal ear sensitivirv curve).

Signal-to-Noise Ratio: 77 db weighted, 72 db unweighted,
for -10 dbm output.

Source Impedance: 30, 250 or 600 ohms matching. For
bridging add proper input pad.

Load Impedance: 600 ohms.
Gain: 41 db.

Output Power: Single frequency output power for less than
1 per cent total harmonics: +16 dbm (38 milliwatts) at
fundamental frequency of 400 cycles: +13 dbm (20 mini;
watts) at fundamental frequency of 50 cycles.

Power Supply (For Complete Amplifier): Filament 6.3
\Olts. 3.2 amperes. Plate 275 volts, 30 milliamperes d-c.
Two of the pre-amplifiers can be supplied from one source
while the other two are supplied from another. 1.6 amperes
filament and 15 milliamperes plate required for each half
of the amplifier. 20 Type Rectifier recommended for power
supply. A single 20 Type Rectifier will supply power for
several 129A Amplifiers.

VACUUM TUBES

Commerrile
Rare/rev Type:
1620 ( or 6J7)
1603

Wetter» Elerlrir
348A or

Qmmi/n Rot/Mira]

mlaa

Mounting: Designed for console mounting: also for rack
mounting on 190 Type Mounting Plate (one per plate).
Type 296 panel required as face mat.

7137,