Western electric 347 schematic
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Page 1
Weflem Electric Company
No.262-B & 347 VACUUM TUBES
Classification-Low-power triodes with indirectly-heated cathodes
These tubes are intended for use in audio-frequency amplifiers where exceptionally low tube
noise is required The)" are designed to minimize hum produced by alternating current operation
of the heater and to minimize microphonic noise.
The two types dirl'er in heater rating, type of base and type of grid cap. In all other respects
they are identical.
The 2623 tube may be used as a replacement for the 262A tube in all applications where the
voltage between heater and cathode is low
Dimensions and Connections-Outline diagrams of the tube and base giving the dimen-
sions and the arrangement of electrode connections to the base terminals for the 2623 tube are
Shown in Figures 1 and 2, Similar information for the 347A tube is shown in Figures 3 and 4.
Base and NIOIInting-The 262B tube employs a small four-pin thrust type base suitable for
use in a Western Electric 143B or similar socket. The base pins are silver-plated. The grid
terminal is a small metal cap located at the top of the bulb,
The 347A tube employs a small shell octal five-pin base. The grid terminal is a skirted minia-
ture metal cap located at the top of the bulb.
These tubes may be mounted in any position.
Copyright 1019, 'cslern Electric company. Incorporated
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Page 2
Ife5rern Elechic Company
NQ262-B & 347 VACUUM TUBES
Average Direct Intel-electrode Capacitances
Grid to plate ......................................... 1.9 ppf.
Grid to cathode and heater ............................ 2.3 ppf.
Plate to cathode and heater ............................ 4.1 puf.
Heater Ratings
2623 Tube 347A Tube
Heater voltage ................... 10.0 6.3 volts, a.c. or d.c.
Nominal heater current ............ 0.32 0.50 ampere
The heater elements of these tubes are designed to operate on a voltage basis and should be
operated at as near the rated voltage as practicable.
Cathode Connection-Where alternating heater voltage is used the cathode should preferably
be connected directly to the mid-point of the heater transformer winding or to the mid-point of a
low resistance connected across the heater terminals. For direct current operation the cath-
ode may be connected to either end of the heater. If voltage is applied between the heater and
cathode, it should be kept low and must not exceed 30 volts.
Characteristics-Typical curves showing plate current as a function of grid voltage for several
values of plate voltage are shown in Figure 5. Corresponding amplification factor, plate resistance
and transconductance characteristics are given in Figures 6, 7 and 8, respectively. Plate current
is shown as a function of plate voltage for several values of grid voltage in Figure 9.
Operating Conditions and Output-Permissible operating plate and grid voltages are in-
cluded within the area, ABCD, in Figure 5. Amplification factor, plate resistance, transconductance
and performance data for a number of typical operating conditions are given in the table. Recom-
mended 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 less severe conditions.
In the last four columns of the table are given the fundamental power output, P..., in milliwatts,
the fundamental voltage output, BM, in peak volts, and the second and third harmonic levels,
F2... and F;,.., in db below the fundamental, corresponding to each of the recommended and maxi-
mum operating conditions for the indicated values of load resistance. The peak value of the
sinusoidal input voltage, Em, in each case is numerically equal to the grid biasing voltage. For
a smaller input voltage, El, the fundamental power, voltage output and the harmonic levels are
given approximately by the following relations:
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