Western electric 205 d schematic

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Wesrem Electric Company
No.205-D VACUUM TUBES

Classification-Moderate power, filamentary triode

Applications

Audio-frequency amplifier or modulator where power outputs of approximately 1 watt or less
are required.

Radio-frequency power amplifier.

Oscillator.

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

Base-Medium, four-pin, bayonet type with the bayonet pin olt'set.

Socket-Four-contact, bayonet-slot type, such as the Western Electric 100M for front of panel
mounting or 1153 for rear of panel mounting.

Mounting Positions-Either vertical or horizontal. If mounted in a horizontal position, the
plane of the filament, which is indicated in Figure 2, should be vertical.

Copyright 1936 Western Electric Company, incorporated

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Western Electric Company
No.205-D VACUUM TUBES

Average Direct Interelectrode Capacitances

A B C
Grid to plate, puf .............................. 4.8 4.3 4.3
Gridtofilament,uuf................... . 5.2 6.4 6.9
Plate to filament, Muf ........................... 3.3 5.2 5.5

Column A;Based tube without socket.

Column B-Tube alone when measured in 100M socket mounted on metal plate; socket and
mounting plate connected to filament.

Column CiTube alone when measured in 1153 socket mounted in metal plate; socket and
mounting plate connected to filament.

filament-Oxide-coated
Filament voltage ............................ 4.5 volts, a.c. or d.c.
Nominal filament current . . ................. 1.6 amperes
The filament of this tube is designed to operate on a voltage basis and should be operated at
as near the rated voltage as is practicable. When alternating-current filament supply is used, the
grid and plate returns should be connected to a center tap on the secondary of the filament trans-
former.

Characteristics-Plate current charcteristics of a typical 205D 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 as functions of plate voltage for several values of grid voltage are
shown in Figure 7. These characteristics are for direct-current filament supply with the grid and
plate voltages measured from the negative end of the filament. When alternating-current filament
supply is used, the same characteristics are applicable if 2.6 is added to the numerical value of each
grid bias.

Microphonic Noise-With a plate voltage of 350 volts, a grid bias of -22.5 volts, and a load
resistance of 100,000 ohms, the mean microphonic noise output level of the 205D tube measured
in a laboratory reference test set is 25 decibels below 1 volt. The range oflevels ofindividual tubes
extends from 16 to 33 decibels below 1 volt. Since microphonic noise depends on the type and
intensity of the mechanical disturbance which produces it, the values given here are useful chiefly
for comparison with the levels of other tubes which have been tested in the same way.

Limiting Conditions for Safe Operation

Class C
Class B Class C B-l Amp.

Class A R-F lt-F Amp. Plate

Amp. Amp. or Osc. Modulated
Maximum direct plate voltage 400 400 400 350 volts
Maximum direct plate current 50 35 50 40 milliamperes
Maximum plate dissipation 14 14 14 10 watts
Maximum direct grid current ~ 10 10 10 milliamperes

Carrier conditions {or use with modulation factors up to 1.0.

Operating Conditions and Output
Class A-Amplifier or Modulator

Permissible operating grid and plate voltages for Class A operation are included within
the area, ABCD, in Figure 3. Amplification factor, plate resistance, transconductance, and
performance data are given in Table I for a number of typical operating conditions represented
by selected points within this area. A less severe operating condition should be selected in
preference to a maximum operating condition wherever possible. The life of the tube at
maximum conditions may be shorter than at less severe conditions.

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