Western electric 268 a brochure

Page 1

5.- a, ..

Wéjfélli Electric

268A Vacuum Tube

Classiflcation-Filamentary air-cooled triode

May be used as an audio-frequency amplifier or as a radio-frequency amplifier, modulator or
oscillator.

Dimensions-Dimensions and outline diagrams are shown in Figures 1 and 2. The overall
dimensions are:

Maximum overall length ............................ 61%;
Maximum diameter ................................ 2%,

Mounting-Four.pin bayonet base for use in a W.E. 143B or similar socket. The anode terminal
is located at the top of the bulb.

Filament-Thoriated tungsten

Filament voltage ................................ 5.0 volts, a.c. or d.c.
Nominal filament current ........................ 3.25 amperes
Average thermionic emission ........................ 0.60 ampere

Copyright 1936 Western Electric Company, Incorporated

268A

Page 2

268A

Average Direct Intereleotrode Capacitances

Platetogrid..... .. ....... _.. .. 2.3mtf
Grid to filament . . . . .. .. . . . , . . . , . 5.4 imf
Plate to filament _ . , ,. .. . ...... . .. .... . . 1.1 pnf

Charactel'iStiCS-Performance data given below are based upon a typical set of conditions.
Variations can be expected with different circuits and tubes.

Figures 3 and 4 give the static characteristics of a typical tube plotted against grid and plate
voltages.

Average Characteristics at maximum direct plate voltage and dissipation Class A
(Eb=750 volts, Ib=25 milliamperes)

Amplification factor. . . . ..... , . .. . . . . .. .... .. . 5

Plate resistance . . . . . ........................... 6250 ohms

Grid to plate transconductance ............. . . . . . . 800 micromhos
Operation

Maximum Ratings

Max. direct plate voltage . . . . . . .. . ............. .. . . 750 volts

Max. direct plate current. . . . . . . . . . . . . .............. , 60 milliamperes

Max. plate dissipation. . . . . . . . .. . . .. .......... 25 watts

Max. direct grid current. . . . .... . . ... ............. ,,, 10 milliamperes

Max. r-f grid cuirent .................................. 3 amperes

Max. frequency for the above ratings... . ,,,,, , 30 megacycles

Max. plate voltage for upper frequency limit of 60 Mc. , . . . 400 volts

Max. plate voltage for frequencies between 30 and 60 MC in proportion

Class A Audio Amplifier or Modulator

Direct plate voltage. . . . . . . .. ............... 750 500 volts
Grid bias , . ........................... . -100 -37 volts
Direct plate current . . . . . . .............. . 25 40 milliamperes
Load impedance . . . , .................. 18000 5000 ohms
Undistorted output. . , . . . . . . ................ 4.0 1.0 watts

Class B Audio Amplifier or Modulator for Balanced 2 Tube Circuit

Direct plate voltage. . ....................... 750 500 volts
Grid bias ................. . . .. ... . .. ... . -120 -70 volts
Direct plate current per tube
No drive ....................... . . . . . 12 12 milliamperes
Max. drive . . . . . . . . ................ 60 60 milliamperes
Plate dissipation... . . ............... . 20 15 watts
Load resistance plate- to-plate .............. . . . 11200 7400 ohms
Load resistance per tube. . . . . . . . . .......... 2800 1850 ohms
Approximate maximum output-2 tubes . . . . . . . . 50 33 watts
Recommended power for driving stage . . ....... 5 5 watts

Class B Radio-Frequency Amplifier

Direct plate voltage. . . ..................... 750 500 volts
Direct plate current for carrier conditions. . . . . . . 50 60 milliamperes
Grid bias .................................... - 165 - 105 volts
Approximate carrier warts for use with 100%

modulation ................................ 12.5 10 watts

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