Western electric 262 a brochure

Page 1

262A

BELL SYSTEM PRACTICES SECTION AB46.335
Transmission Engineering and Data Issue 1, September 1936
Vacuum Tube Data A T & T Co Standard

Wafer/7 Electric
262A Vacuum Tube

Classification-Low-power triode with indirectly-heated cathode

The 262A tube is designed to minimize hum produced by alternating current operation of the
heater, and to minimize microphonic noise.

Application-Audie-frequency amplifier where alternating current is used for heating the cathode
and exceptionally low tube noise is required

Dimensions-Dimensions. outline diagrams of the tube and base. and the arrangement of electrode
connections to the base terminals are shown in Figures 1 and 2.

Base-Medium, four-pin thrust type having silver-plated pins. Small metal cap grid terminal
at the top of the bulb.

Socket-Standard, four-contact type, preferably provided with silver-plated contacts such, as the
Western Electric 143B socket.

Copyright 1936, Western Electric Company, Incorporated

Page 2

Mounting Positions-The 262A tube may be mounted in any position.

Average Direct Interelectrode Capacitances

Grid to plate ................ . . ............... H . . 1.9 Mflf.

Grid to cathode and heater. . . . ........... . . ....... . . . 1.8 ##f-

Plate to cathode and heater. . . ........................ 4.0 paf.
Heater Rating

10.0 volts, a.c. or d.c.
0.32 ampere

Heater voltage .............
Nominal heater current ........

The heater element of this tube is designed to operate on a voltage basis and should be operated
at as near the rated voltage as is practicable.

Cathode COBDECtion-Preferably direct to the mid-point of the heater transformer winding
or to the mid-point of a low resistance connected across the heater terminals, where alternating
heater voltage is used. This connection usually reduces the hum produced in the tube. Where
voltage must be applied between the heater and cathode, it should be kept as low as possible and
should not exceed 90 volts.

Characteristics-Plate current characteristics of a typical 262A tube are shown in Figure 3 as
functions of grid voltage for several values of plate voltage. Corresponding amplification factor,
plate resistance and transconductance characteristics are given in Figures 4, 5, and 6, respectively.
Plate current characteristics are given as functions of plate voltage for several values of grid voltage

in Figure 7.

Operating Conditions and Output-Permissible operating plate and grid voltages are in-
cluded within the area, ABCD, in Figure 3. A number of recommended and maximum operating
conditions represented by selected points within this area and the corresponding values of amplifi-
cation factor, plate resistance and transconductance are given in the table on page 4. Recommended
conditions or others of no greater severity should be selected in preference to maximum conditions
wherever possible. The life of the tube at maximum conditions may be shorter than at the recom-

mended conditions.

In the latter part of the table are given the fundamental power output, Pm, in milliwatts, the
fundamental voltage output, Epm, in peak volts, and the second and third harmonic levels, Fan and
F311;, in db below the fundamental, corresponding to each of the recommended and maximum
operating conditions for the indicated values of load resistance, R. The fundamental output is
given in terms of power for values of load resistance equal to and double the value of the plate
resistance, rp, and in terms of voltage for values of load resistance five times the plate resistance.

The peak value of the sinusoidal input voltage, Egm, in each case is numerically equal to the
grid biasing voltage. For a smaller input voltage, Eg, the fundamental power and voltage output
and the harmonic levels are given approximately by the following relations:

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