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Tube Substitutions for:
845
Triode, vacuum

Type	Substitutes	Base Diagram
845	VT-43, VT43
Web References	845 (RCA (HB3)) @ Franks Electron Tubes 845 (Amperex) @ Franks Electron Tubes 845 @ RadioMuseum.org

RCA Type 845
MODULATOR AND A-F POWER AMPLIFIER


MECHANICAL DATA

Bulb	T-18
Base	Jumbo 4_Large Pin
Basing	S4E

ELECTRICAL DATA

FILAMENT CHARACTERISTICS

Filament Voltage (AC)	10	Volts
Filament Current	3.25	Amps

MAXIMUM RATINGS
As A-F Power Amplifier and Modulater - Class A

D-C Plate Voltage	1250	Volts
Plate Dissipation	75	Watts

TYPICAL OPERATING CONDITIONS
As A-F Power Amplifier and Modulater - Class A

D-C Plate Voltage	750	1000	1250	Volts
Grid Voltage	-98	-155	-209	Volts
Peak Grid Swing	93	150	204	Volts
D-C Plate Current	95	65	52	Ma
Load Reistance	3400	9000	16000	Ohms
Undistorted Power Output	15	21	24	Watts

INSTALLATION
The base of the RCA-845/545 fits the standard transmitting, four-contact socket such as the RCA type UT-541. The scket should be mounted so that the tube will operate in a vertical position with the base end down.

APPLICATION
As a Class A audio-frequency amplifier or modulater, the 845/545 is capable of delivering 24 watts of audio-frequency power with very low distortion. Typical operating conditions are shown under MAXIMUM RATINGS and TYPICAL OPERATING CONDITIONS.
Grid bias for this typ of service may be obtained from a seperate voltage source or by means of a cathode-biasing resistor. When a group o f845/545's is operated in parallel, it is necessary to make provision for individual adjustment of grid bias to insure that the plate dissipation of each tube does not exceed the masimum value of 75 watts. This my be accomplished by means of a tapped "c" battery, or if self-bias is used, by means of a variable cathode resistor for each tube. Separate filament windings are necessary, of course, for each tube that is self-biased; each cathode resistor should be shunted by a filter network to avoid degenerative effects at low audio frequencies.
In cases where the input circuit to the 845/545 is resistance or impedance coupled, the resistance in teh grid circuit should not be made too high. A resistance of one-half megohm for one 845/545 may be taken as a safe maximum when self-bias is used. Without self-bias, the grid resistance should not exceed 100000 ohms.
If more output is desired than can be obtained from a single 845, two 845's mayb be operated in parallel or push-pull, without an increase in grid-signal voltage. The push-pull connection will give twice the output at the same grid bias, but requires twice the input signal. Output slightly greate than twice the single tube valube can be obtained from the push-pull connection by increasing the bias. In the latter case, the output is limited almost entirely by 3rd harmonic distortion. When two 845's are operated together (parallel or push-pull), the values of the self-biasing resistors will be approximately one-half the values given above for a single tube. When two 845's are operated in push-poull, the filter network acreoss the self-biasing resistor may be omitted. When a number of tubes are operated in parallel, a non-inductive resistance of 10 to 100 ohms should be placed in series with each grid lead, next to the tube socket, to prevent parasitic oscillations.
An output device should be used to transfer power effiently to the windings of the reproducing unit when the RCA-845/545 is used as an audio-frequency amplifier.


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