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Nuvistor Tubes (all numbers) ·Triode

7895

Industrial high-mu Nuvistor triode intended for a wide variety of industrial amplifier and control applications.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
1
Base
TWELVAR 5 pin
Socket code
-
Base pins
-
Nominal heater
6.3 V / 135 mA

Description

7895 — Special-Quality High-Mu Industrial Nuvistor Triode

Compact metal-ceramic receiving triode for low-noise industrial amplification, with controlled electrical tolerances and extensive shock, vibration, insulation, and life testing.

Overview

The 7895 is a high-mu Nuvistor triode intended for a wide range of industrial applications. RCA, Siemens, and Philips describe a compact metal-shell device capable of substantial voltage amplification while maintaining close electrical tolerances, low noise, and mechanical robustness. The Siemens document describes universal high-mu operation and emphasizes long life, reliability, shock resistance, and vibration resistance. Philips identifies the 7895 as a special-quality industrial triode.

The tube's characteristic operating point uses a 110 V plate supply, 150 Ω cathode resistor, and approximately 7 mA plate current, with an amplification factor of 64 and transconductance of 9.4 mA/V.

Construction and Heater

The 7895 uses an indirectly heated coated cathode in a compact metal-shell Nuvistor envelope. Its base is the E5-65 medium ceramic-wafer five-contact Twelvar arrangement, with 12AQ basing. RCA specifies an indexed Nuvistor socket.

PropertyManufacturer value
Heater voltage6.3 V, ±10% in RCA data
Heater current135 mA nominal
Heater current production range125–145 mA
Calculated heater power0.85 W
Maximum overall length0.800 in
Maximum seated length0.625 in
Maximum diameter0.440 in
Approximate weight1.9–2 g
Mounting positionAny

The heater can operate from AC or DC. The maximum peak heater-to-cathode voltage is ±100 V.

Base connections

The RCA underside-view drawing identifies pin 2 as plate, pin 4 as control grid, pin 8 as cathode, and pins 10 and 12 as heater. Pin 1 and its associated internally connected positions must not be used as external circuit terminals. The large index lug and shortened pin establish orientation.

Typical Class A1 Characteristics

CharacteristicValue
Plate supply voltage110 V
Grid supply voltage0 V
Cathode resistor150 Ω
Plate current7.0 mA
Transconductance9,400 µmhos (9.4 mA/V)
Amplification factor64
Plate resistanceApproximately 6,800 Ω
Grid voltage at 10 µA plate currentApproximately −4 V

The approximate triode relationship μ ≈ gₘ × rₚ gives 0.0094 S × 6,800 Ω ≈ 64. The amplification factor is an intrinsic small-signal characteristic; loaded voltage gain depends on the external circuit.

RCA's equipment-design limits include 5.5–8.8 mA plate current, 7.9–10.9 mA/V transconductance, and 54–74 amplification factor at its defined acceptance conditions.

High-Frequency and Noise Characteristics

Siemens publishes a 4.7 dB noise figure at 200 MHz under noise-matched conditions and an equivalent input noise resistance of approximately 0.8 kΩ at that frequency. These are specific high-frequency measurements, not universal values for every amplifier configuration.

The low interelectrode capacitances and metal-ceramic construction support the high-frequency industrial amplifier applications documented by the manufacturers.

Direct Interelectrode Capacitances

MeasurementNominal
Grid to plate0.9 pF
Grid to cathode, shell, and heater4.2 pF
Plate to cathode, shell, and heater1.7 pF
Plate to cathode0.22 pF
Heater to cathode1.3 pF

Philips and RCA give production ranges of 0.8–1.0 pF grid-to-plate, 3.4–5.0 pF input, 1.3–2.1 pF output, and 1.0–1.6 pF heater-to-cathode capacitance.

Industrial Maximum Ratings

ParameterLimit
Plate supply voltage330 V
Plate voltage110 V
Plate dissipation1 W
Cathode current15 mA
Negative grid voltage55 V
Peak positive grid voltage2 V
Grid current2 mA
Grid-circuit resistance, fixed bias0.5 MΩ
Grid-circuit resistance, cathode bias1 MΩ
Metal-shell temperature150°C under specified ratings

The higher plate-supply limit must not be confused with the maximum permissible actual plate voltage.

Industrial Reliability Qualification

RCA's detailed technical sheet specifies 1,000 g peak-impact shock testing, 2.5 g fatigue vibration for 48 hours at 60 Hz, variable-frequency vibration-noise measurements, low-pressure voltage breakdown testing, heater cycling, and multiple life-performance tests.

Under specified 1 g vibration testing, RCA limits RMS output noise to 35 mV at 50–1,000 Hz, 60 mV at 3–6 kHz, and 500 mV at 6–15 kHz. The low-pressure test simulates altitudes up to 100,000 feet.

RCA specifies at least 2,000 heater on/off cycles in its heater-cycling qualification. Its life tests include 20-hour stabilization, 100-hour survival, and 1,000-hour conduction and standby evaluations. Siemens separately describes service life exceeding 10,000 hours under its quality specification.

These are manufacturer-specific qualification and reliability statements rather than a single unconditional guaranteed service-life rating.

Technical Summary

The 7895 is a 6.3 V / 135 mA high-mu Nuvistor industrial triode, with approximately 64 amplification factor, 9.4 mA/V transconductance, 6.8 kΩ plate resistance, and 7 mA plate current at the principal Class A1 test point.

Its compact metal-ceramic construction, low interelectrode capacitances, documented 200 MHz noise characteristics, and extensive industrial quality testing make it a specialized receiving amplifier for applications requiring reliable, stable electrical performance.

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
TWELVAR 5 pin
Socket code
-
Base pins
-
Nominal heater voltage
6.3 V
Nominal heater current
135 mA
Parallel heater voltage
-
Parallel heater current
-
Series capable
No

TWELVAR 5 pin - 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

Triode

X-ray radiationInterelectrode capacitances
Plate resistance
6800 Ω
Transconductance
0.0094 S
Amplification factor
64
Max plate voltage
125 V
Max plate dissipation
1 W
Max cathode current
15 mA

Published promoted values applied where semantically applicable; additional source-table values retained in TUBE_SECTION_PARAMETER.

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

1963 Siemens

Published operating points and test conditions from this source.

SECTION 1

Triode

Other

  • Heater voltage

    6.3 V

  • Heater current

    135 mA

Characteristics

  • Transconductance

    9400 µS

    Nominal/Bogey

  • Amplification factor

    64

    Nominal/Bogey

Data set 02

1971 RCA HB3 Binder 3 of 7

Published operating points and test conditions from this source.

SECTION 1

Triode

Characteristics

  • Current at 6.3 volts — published value 1

    6.3 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Current at 6.3 volts — published value 2

    0.135 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Grid to plate

    0.9

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Grid to cathode, shell, and heater

    4.2

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Plate to cathode, shell, and heater

    1.7

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Plate to cathode

    0.22

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Heater to cathode

    1.3

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Plate Supply Voltage

    110 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Grid Supply Voltage

    0 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Plate Resistance (Approx )

    6800 ohm

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Transconductance

    9400

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Plate Current

    7 mA

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Pin 2 —Plate

    2

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Pin 4 —Grid

    4

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Pin 10 —Heater

    10

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Pin 12 —Heater

    12

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • PLATE VOLTAGE

    110 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Heater Current — published value 1

    1

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Heater Current — published value 2

    0.125

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Heater Current — published value 3

    0.145

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Grid to plate — published value 1

    2

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Grid to plate — published value 2

    0.8

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Grid to plate — published value 3

    1

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • heater — published value 1

    2

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • heater — published value 2

    3.4

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • heater — published value 3

    5

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • heater — published value 1

    2

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • heater — published value 2

    1.3

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • heater — published value 3

    2.1

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Heater to cathode — published value 1

    2

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Heater to cathode — published value 2

    1

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Heater to cathode — published value 3

    1.6

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Plate to cathode — published value 1

    2

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Plate to cathode — published value 2

    0.16

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Plate to cathode — published value 3

    0.28

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Plate Current (1) — published value 1

    1 mA

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Plate Current (1) — published value 2

    3 mA

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Plate Current (1) — published value 3

    5.5 mA

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Plate Current (1) — published value 4

    8.8 mA

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Plate Current (2) — published value 1

    2

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Plate Current (2) — published value 2

    1

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Plate Current (2) — published value 3

    4

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Plate Current (2) — published value 4

    50

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Transconductance (1) — published value 1

    1

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Transconductance (1) — published value 2

    3

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Transconductance (1) — published value 3

    7900

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Transconductance (1) — published value 4

    10900

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Transconductance (2) — published value 1

    2

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Transconductance (2) — published value 2

    3

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Transconductance (2) — published value 3

    5

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Transconductance (2) — published value 4

    6900

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Reverse Grid Current — published value 1

    1

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Reverse Grid Current — published value 2

    6

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Reverse Grid Current — published value 3

    0.1

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Amplification Factor — published value 1

    1

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Amplification Factor — published value 2

    3

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Amplification Factor — published value 3

    54

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Amplification Factor — published value 4

    74

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Note 1 — published value 1

    1 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Note 1 — published value 2

    6.3 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Note 3 — published value 1

    3 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Note 3 — published value 2

    110 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Note 3 — published value 3

    150 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • and cathode—Dyp ass capacitor = 1000 µf

    1000

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Note 5 — published value 1

    5 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Note 5 — published value 2

    5.7 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Nate 6 — published value 1

    6 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Nate 6 — published value 2

    150 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Nate 6 — published value 3

    1 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Nate 6 — published value 4

    7 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

Other

  • PLATE SUPPLY VOLTAGE

    330 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Negative-bias value

    55 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • GRID CURRENT

    2 mA

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • PLATE CURRENT

    20 mA

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • CATHODE CURRENT

    15 mA

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • PLATE DISSIPATION

    1 mA

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Heater negative with respect to cathode

    100 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • Heater positive with respect to cathode

    100 V

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • For fixed-bias operation — published value 1

    0 mA

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • For fixed-bias operation — published value 2

    5 mA

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

  • For cathode-bias operation

    1 mA

    Published datasheet value; multiple numbers on a source row represent separate limits or operating conditions.

Data set 03

1975 RCA RC30

Published operating points and test conditions from this source.

SECTION 1

Triode

Capacitance

  • Grid to Plate Capacitance

    1.6 pF

Other

  • Plate Supply Voltage

    330 V

  • Typical Plate Supply Voltage

    110 V

    ClassA

  • Typical Plate Current

    7 mA

    ClassA

Data set 04

1999 Philips 0-D

Published operating points and test conditions from this source.

SECTION 1

Triode

Other

  • Anode voltage in cold condition

    - to 330 V

    Published datasheet value

Characteristics

  • Typical anode current

    7 mA

    Published datasheet value

  • Anode current range

    5.5 to 8.8 mA

    Published datasheet value

  • Transconductance range

    7.9 to 10.9 mA/V

    Published datasheet value

  • Amplification factor range

    54 to 74

    Published datasheet value

  • Plate resistance

    6.8 kΩ

    Published datasheet value

  • Grid-to-other capacitance

    4.2 pF

    Published datasheet value

  • Anode-to-other capacitance

    1.7 pF

    Published datasheet value

  • Anode-grid capacitance

    0.9 pF

    Published datasheet value

  • Anode-cathode capacitance

    0.22 pF

    Published datasheet value

  • Cathode-heater capacitance

    1.3 pF

    Published datasheet value