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Specialized - Photo Tube ·CameraPickup

1850A

RCA iconoscope television camera pickup tube optimized particularly for motion-picture film and slide scanning.

Directly heatedCold cathodeCommon cathodeDissimilarSpecialized
Sections
1
Base
-
Socket code
UX6
Base pins
-
Nominal heater
-

Description

1850A — Iconoscope Television Camera Tube

The 1850A is a specialized television camera tube of the iconoscope type designed primarily for pickup from motion-picture film or slides. It is characterized by a very high signal-to-noise ratio combined with relatively low sensitivity. For applications requiring higher sensitivity, such as outdoor and studio live pickups, other tube types like the image orthicon are typically preferred.

Mechanical and Physical Characteristics

The 1850A utilizes electrostatic focusing and magnetic deflection to control its electron beam. The nominal deflection angle is approximately 55 degrees. The tube is physically large and requires specific mounting arrangements to function correctly.

  • Mounting Position: The tube must be mounted such that its mosaic lies in a vertical plane.
  • Envelope Dimensions:
    • Maximum width of the mounted tube: 8-1/8 inches
    • Height of the mounted tube: 10-3/16 inches ± 3/4 inch
    • Depth of the mounted tube: 12-13/16 inches ± 3/4 inch
  • Base: Long Medium-Shell Small 6-Pin base.
  • Caps: Two medium caps (conforming to JETEC No. C1-5).
  • Deflecting-Coil Requirements: The deflecting yoke must have a minimum inside diameter of 1-1/2 inches and a maximum length of 2-1/4 inches.

Heater and Terminal Connections

The 1850A features an indirectly heated, unipotential cathode. The heater is designed for either AC or DC operation.

Heater ParameterValue
Nominal Voltage6.3 V ± 10%
Nominal Current0.6 A

Pinout Configuration

The connections for the 6-pin base, viewed from the bottom, are assigned as follows:

  • Pin 1: Heater
  • Pin 2: Grid No. 2
  • Pin 3: Grid No. 3
  • Pin 4: Grid No. 1
  • Pin 5: Cathode
  • Pin 6: Heater

In addition to the base pins, the tube features external caps and manufacturing-specific terminals:

  • SJ Cap: Signal Electrode
  • G4 Cap: Grid No. 4 (Collector)
  • Caps A, B, C, D: Manufacturing caps. No external connections should be made to these terminals.

Interelectrode Capacitances

The capacitance values of the 1850A electrodes are measured under specified shielding conditions:

  • Grid No. 1 to all other electrodes: 6.5 µµF
  • Signal Electrode to Grid No. 4: 10 µµF (measured with an external shield)

Absolute Maximum Ratings

The following absolute maximum limits must not be exceeded to ensure the longevity and proper operation of the tube:

ParameterMaximum Rating
Average Mosaic Illumination (averaged over max 1 second)50 ft-c
Operating Temperature of Bulb (at the large end)40 °C
Signal-Electrode Voltage1200 V
Grid-No. 4 (Collector) Voltage1200 V
Grid-No. 3 Voltage450 V
Grid-No. 2 Voltage1200 V
Grid-No. 1 Negative Bias Voltage125 V
Grid-No. 1 Positive Bias Voltage0 V
Peak Heater-Cathode Voltage (Heater negative with respect to cathode)125 V
Peak Heater-Cathode Voltage (Heater positive with respect to cathode)10 V
Grid-No. 4 Current0.5 µA

Typical Operation and Characteristics

Under typical operating conditions, the 1850A is configured with the following electrode potentials and circuit values:

  • Signal-Electrode Voltage: 1000 V
  • Grid-No. 4 Voltage: 1000 V
  • Grid-No. 2 Voltage: 1000 V
  • Grid-No. 4 Current (unilluminated mosaic, including leakage): 0.1 to 0.2 µA
  • External Load Resistance: 0.1 MΩ
  • Maximum Grid-No. 1-Circuit Resistance: 1.0 MΩ
  • Minimum Peak-to-Peak Blanking Voltage: 20 V

Calculated Operating Voltages

  • Grid-No. 3 Voltage (Beam Focus): Calculated as 24% to 36% of the Grid-No. 4 voltage, yielding 240 V to 360 V based on a 1000 V input.
  • Grid-No. 1 Voltage for Pattern Cutoff: Calculated as 7% of the Grid-No. 4 voltage, yielding -70 V based on a 1000 V input.

Deflection and Signal Characteristics

When operated with a standard deflecting yoke (such as the RCA Type No. 201D76), the approximate peak-to-peak deflecting currents are:

  • Horizontal Deflecting Current: 600 mA (peak-to-peak)
  • Vertical Deflecting Current: 140 mA (peak-to-peak)

Under typical operating conditions, the ratio of the peak-to-peak highlight video-signal current to the RMS noise current is approximately 100.

Mosaic Illumination Requirements

The required illumination on the mosaic depends on the source material:

  • Steady highlight value for slides: 4 to 6 ft-c
  • Average pulsed highlight value for motion-picture film: 10 to 20 ft-c

Electro-Optical Characteristics and Curves

The spectral sensitivity of the 1850A spans the entire visible spectrum, covering approximately 3500 to 7000 Å. The peak sensitivity is located in the blue region of the spectrum, at approximately 4500 Å, when evaluated under equal values of radiant flux across all wavelengths.

The signal-output characteristic of the tube exhibits a non-linear relationship between the highlight illumination of the mosaic and the resulting signal output. Under continuous daylight fluorescent lighting with balanced scene blacks and whites, an optimum back lighting level, and a beam current of 0.2 µA, the signal output rises from approximately 0.05 µA at an illumination of 0.3 ft-c to approximately 0.23 µA at 20 ft-c. The output curve demonstrates a characteristic knee, indicating a saturation effect at higher illumination levels.

Socket description

Small 6-contact

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
-
Socket code
UX6
Base pins
-
Nominal heater voltage
-
Nominal heater current
-
Parallel heater voltage
-
Parallel heater current
-
Series capable
No

Terminal pinout

Electrical assignments shared by every tube using this base designation.

No verified pinout is recorded for this base designation.

Section ratings

1 physical section, each with unique specifications.

Section 1

CameraPickup

X-ray radiationInterelectrode capacitances

No fixed ratings are recorded for this section.

Source-derived section; promoted fields populated where applicable.

Source-dependent data

Operating conditions by source

Each block preserves the test conditions and published values from one reference. Values from different sources are intentionally kept separate.

Data set 01

1940 RCA

Published operating points and test conditions from this source.

SECTION 1

CameraPickup

Other

  • illumination of

    6

    illumination of 4 to 6 foot-candles on the mosaic for slides and an average

  • value of pulsed highlight illumination of

    20

    value of pulsed highlight illumination of 10 to 20 foot-candles for motion—

  • Voltage (AC or DCY . v v v v v

    10 V

    Voltage (AC or DCY . v v v v v 6 0 v 4 v v v v u s 6. 3+ 10% volts

  • Current. & & & &

    6 A

    Current. & & & & 4 4 e e 6 s 4 e e e s s e e s e 0. 6 ampere

  • SIGNAL-ELECTRODE VOLTAGE + &«

    1200 V

    SIGNAL-ELECTRODE VOLTAGE + &« 4 ¢ ¢ 4 o o e o o « s & & = 1200 max. volts

  • GRID-No,

    1200 V

    GRID-No,4 (COLLECTOR) VOLTAGE, « & « ¢ s ¢ o o s & 2 s » 1200 max. volts

  • GRID=NO

    450 V

    GRID=NO.3 VOLTAGE. ¢ ¢ « ¢ o + o o 5 o s o o s s « » 2 @ 450 max. volts

  • GRID-N0.,

    200

    GRID-N0.,2 VOLTAGE., . . ¢« ¢ ¢ & o o o s o o o o o o s o {200 max. voits

  • Negative bias value, . . . + . « . « . o o«

    125 V

    Negative bias value, . . . + . « . « . o o« . . 125 max. volts

  • Positive bias value. . +« « « + « v v + &« +v « &

    0 V

    Positive bias value. . +« « « + « v v + &« +v « & 0 max. volts

  • Heater negative with respect to cathode

    125 V

    Heater negative with respect to cathode. . . . . 125 max. volts

  • Heater positive with respect to cathode

    10 V

    Heater positive with respect to cathode. . . . . 10 max. volts

  • GRID~No

    0.5

    GRID~No.4 CURRENT. . v v ¢ v 4 o & o & o « + « = & 0.5 max. Hamp

  • Signal-Electrode Voltage . . . . « « + « + + « o &

    1000 V

    Signal-Electrode Voltage . . . . « « + « + + « o & 1000 volts

  • Grid-No

    1000 V

    Grid-No.4 Voltage., . . . « ¢ 4 ¢ ¢ a s+ o v 4 & o« 1000 volts

  • Grid-No

    3

    Grid-No.3 Voltage (Beam Focus)——

  • 24% to 36% of Grid-No.4 Voltage. . . . . . 240 to 360 volts

    360 V

    24% to 36% of Grid-No.4 Voltage. . . . . . 240 to 360 volts

  • Grid=-No

    1000 V

    Grid=-No.2 Voltage., . . . + . + « =« « « ¢+ & & & 1000 volts

  • 7% of Grid-No.4 Voltage. . . . « « + « . . =70 volts

    70 V

    7% of Grid-No.4 Voltage. . . . « « + « . . =70 volts

  • Grid-No

    0.2

    Grid-No.4 Current (With no illumination on mosaic) 0.1 to 0.2 Hamp

  • Minimum Peak-to-Peak Blanking Voltage

    20 V

    Minimum Peak-to-Peak Blanking Voltage. . . . . . . 20 volts

  • Vertical (Peak to peak). . « « o o « ¢ s o« o » |

    40 mA

    Vertical (Peak to peak). . « « o o « ¢ s o« o » |40 ma

  • Grid-No.|-Circuit Resistance « + « « o« + ¢« » o o

    0

    Grid-No.|-Circuit Resistance « + « « o« + ¢« » o o 1,0 max. megohm

  • | | BEAM CURRENT

    0.2

    | | BEAM CURRENT: 0.2 MICROAMPERE

  • 92CM—-6404 F2CM

    -6404

    92CM—-6404 F2CM

  • 92CM~489IR3

    489

    92CM~489IR3

  • AR'

    2.5

    AR' 1S 2.5° MAX. ROTATION OF MOSAIC

Characteristic

  • External Load Resistance . . . . + . + + ¢ v v o o

    0.1

    External Load Resistance . . . . + . + + ¢ v v o o 0.1 megohm