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Power - Beam Single (NOT sweep) (under 10W) ·BeamPower

12CA5

Miniature beam-power output tube designed for audio-frequency power stages in radio and television receivers, combining compact size with useful Class-A output capability.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
1
Base
7CV
Socket code
B7G
Base pins
7
Nominal heater
12.6 V / 600 mA

Description

12CA5 — Beam Power Pentode

An indirectly heated miniature beam power tube designed for audio-frequency power output stages in series-heater television and radio receivers.

Overview

The 12CA5 is a miniature beam power tube (also classified as a beam pentode) designed primarily for service in the audio-frequency (AF) power output stage of television and radio receivers. It is specifically engineered for use in equipment employing a series heater-string arrangement, particularly those with a 600 mA series-heater current.

The 12CA5 is characterized by high power sensitivity and efficiency when operating at relatively low plate and screen-grid voltages. Except for its heater ratings and specific heater-cathode voltage limits, the 12CA5 is electrically identical to the 6CA5 and 25CA5 vacuum tubes.

Construction, Mechanical Specifications, and Pinout

The 12CA5 is constructed with a T-5-1/2 glass bulb and a small-button miniature 7-pin base (JETEC No. E7-1). The tube features a coated unipotential cathode and can be operated in any mounting position.

Physical Dimensions

  • Maximum Overall Length: 2-5/8 inches
  • Maximum Seated Length: 2-3/8 inches
  • Length from Base Seat to Bulb Top (excluding tip): 2 ± 3/32 inches
  • Maximum Diameter: 3/4 inch

Pinout and Basing (7CV)

The tube utilizes the 7CV basing arrangement. Viewed from the bottom of the tube, the pin connections are assigned as follows:

  • Pin 1: Cathode, Grid No. 3 (Suppressor Grid / Beam Plates)
  • Pin 2: Grid No. 1 (Control Grid)
  • Pin 3: Heater
  • Pin 4: Heater
  • Pin 5: Grid No. 1 (Control Grid)
  • Pin 6: Grid No. 2 (Screen Grid)
  • Pin 7: Plate

The control grid (Grid No. 1) is internally connected to both Pin 2 and Pin 5 to facilitate flexible circuit layout and heat dissipation.

Direct Interelectrode Capacitances

When measured without an external shield, the approximate interelectrode capacitances of the 12CA5 are:

  • Grid No. 1 to Plate: 0.5 µµF
  • Input (Grid No. 1 to Cathode & Grid No. 3, Grid No. 2, and Heater): 15 µµF
  • Output (Plate to Cathode & Grid No. 3, Grid No. 2, and Heater): 9 µµF

Heater Characteristics and Series-String Design

The heater of the 12CA5 is designed for series-string operation, where its thermal characteristics are tightly controlled to prevent voltage surges during the receiver's warm-up cycle.

Heater ParameterValue
Nominal Heater Voltage (AC or DC)12.6 V
Nominal Heater Current0.6 A
Average Heater Warm-up Time11.0 seconds

Heater Power Calculation

Using the nominal heater voltage (VfV_f) and heater current (IfI_f), the nominal power consumption (PfP_f) of the 12CA5 heater is calculated as: Pf=Vf×If=12.6 V×0.6 A=7.56 WP_f = V_f \times I_f = 12.6\text{ V} \times 0.6\text{ A} = 7.56\text{ W}

Controlled Warm-up Specification

The heater warm-up time is defined as the time required for the voltage across the heater to reach 80% of its rated voltage after applying four times the rated heater voltage (50.4 V) to a circuit consisting of the tube heater in series with a resistance equal to three times the nominal heater operating resistance. This controlled warm-up minimizes transient voltage surges when the tube is operated in series with other similarly controlled tubes.

Heater-Cathode Voltage Ratings

Because the heater is operated in a series string, it may experience high potential differences relative to the cathode. The maximum ratings for heater-cathode voltage depend on the polarity and the specific manufacturer rating system:

  • Heater Positive with Respect to Cathode:
    • Total DC and Peak: 200 V max
    • DC Component / Average Value: 100 V max
  • Heater Negative with Respect to Cathode:
    • Total DC and Peak: 300 V max (some specifications list 200 V max)
    • DC Component / Average Value: 200 V max (some specifications list 100 V max)

Maximum Ratings (Design-Center Values)

The following maximum ratings must not be exceeded under Class A1 amplifier service:

ParameterMaximum Value
Plate Voltage130 V
Grid No. 2 (Screen-Grid) Voltage130 V
Grid No. 1 (Control-Grid) Voltage, Positive-bias value0 V
Plate Dissipation5.0 W
Grid No. 2 Input1.4 W
Bulb Temperature (at hottest point on bulb surface)180 °C

Maximum Circuit Resistance

To ensure bias stability and prevent thermal runaway, the resistance in the Grid No. 1 circuit is restricted based on the biasing method:

  • For Fixed-Bias Operation: 0.1 MΩ maximum
  • For Cathode-Bias Operation: 0.5 MΩ maximum

Typical Operation and Class A1 Amplifier Characteristics

The 12CA5 is optimized to deliver high output power from low supply voltages. The typical operating conditions and electrical characteristics for Class A1 amplifier service are documented at two primary operating points:

ParameterOperating Point AOperating Point B
Plate Voltage110 V125 V
Grid No. 2 Voltage110 V125 V
Grid No. 1 Voltage−4.0 V−4.5 V
Peak AF Grid No. 1 Voltage4.0 V4.5 V
Zero-Signal Plate Current32 mA37 mA
Maximum-Signal Plate Current31 mA36 mA
Zero-Signal Grid No. 2 Current (Approx.)3.5 mA4.0 mA
Maximum-Signal Grid No. 2 Current (Approx.)7.5 mA11.0 mA
Plate Resistance (Approx.)16,000 Ω15,000 Ω
Transconductance8,100 µmhos9,200 µmhos
Load Resistance3,500 Ω4,500 Ω
Total Harmonic Distortion (Approx.)5%6%
Maximum-Signal Power Output1.1 W1.5 W

These operating points demonstrate the high sensitivity of the 12CA5: with a peak grid signal of only 4.5 V, the tube can deliver 1.5 W of audio output power into a 4,500 Ω load.

Operation and Plate Characteristics

The average plate characteristics curves plot plate current (IbI_b) and screen-grid current (Ic2I_{c2}) against plate voltage for various control-grid bias voltages (E[c1](/tubes/C1)E_{[c1](/tubes/C1)}) ranging from 0 V down to −10 V, with the screen grid (Ec2E_{c2}) held constant at 125 V.

The curves exhibit the typical knee characteristic of beam power tubes, where plate current rises rapidly at low plate voltages and then flattens out, becoming relatively independent of plate voltage over the normal operating range. This sharp knee allows for a wide plate-voltage swing, contributing to the tube's high efficiency and power output at low supply voltages.

The operation characteristics curves illustrate how power output, total harmonic distortion, plate current, and screen-grid (Grid No. 2) current vary as a function of load resistance under typical operating conditions (with Ef=12.6 VE_f = 12.6\text{ V}, plate voltage = 125 V, screen voltage = 125 V, grid bias = −4.5 V, and an RMS signal voltage of 3.2 V):

  • Power Output: Peaks near the recommended load resistance of 4,500 Ω, reaching approximately 1.5 W.
  • Total Harmonic Distortion: Shows a minimum around 3,000 Ω (at approximately 5%) and rises to about 6% at 4,500 Ω, and up to 10% as the load resistance increases toward 7,000 Ω.
  • Plate Current: Decreases steadily as load resistance increases, falling from over 45 mA at 1,000 Ω to under 30 mA at 7,000 Ω.
  • Grid No. 2 Current: Increases with higher load resistance, rising from about 6 mA at 1,000 Ω to over 13 mA at 7,000 Ω.

Related Designations and Comparisons

The 12CA5 belongs to a family of identical beam power tubes that differ only in their heater configurations:

  • 6CA5: Designed for parallel heater circuits, requiring a 6.3 V heater supply at 1.2 A.
  • 25CA5: Designed for series-string circuits, requiring a 25 V heater supply at 0.3 A.

While the 12CA5 shares its internal structure, electrode geometry, and Class A1 typical operating characteristics with the 6CA5 and 25CA5, they are not direct drop-in replacements for one another due to these differing heater voltage and current requirements, as well as differences in their maximum heater-cathode voltage ratings.

Technical Summary

The 12CA5 is a 7-pin miniature beam power tube designed for Class A1 audio power output service in series-string radio and television receivers. Operating with a 12.6 V, 0.6 A heater with controlled warm-up characteristics, it delivers up to 1.5 W of audio power from low supply voltages (110–125 V) with high sensitivity. Its physical construction, standardized 7CV pinout, and robust heater-to-cathode insulation make it highly optimized for compact, transformerless consumer electronics of its era.

Socket description

Miniature 7-contact

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
7CV
Socket code
B7G
Base pins
7
Nominal heater voltage
12.6 V
Nominal heater current
600 mA
Parallel heater voltage
-
Parallel heater current
-
Series capable
No

7CV - Terminal pinout

Electrical assignments shared by every tube using this base designation.

TerminalSectionConnectionEvidence
PIN1G3AG3 — Suppressor GridGroup 7CV1

EIA chart transcription; independent manufacturer verification pending

Unverified

EIA Base Connections, printed page 128, 7CV

PIN1KAK — CathodeGroup 7CV1

EIA chart transcription; independent manufacturer verification pending

Unverified

EIA Base Connections, printed page 128, 7CV

PIN2G1AG1 — Control Grid

EIA chart transcription; independent manufacturer verification pending

Unverified

EIA Base Connections, printed page 128, 7CV

PIN3H—H — Heater

EIA chart transcription; independent manufacturer verification pending

Unverified

EIA Base Connections, printed page 128, 7CV

PIN4H—H — Heater

EIA chart transcription; independent manufacturer verification pending

Unverified

EIA Base Connections, printed page 128, 7CV

PIN5G1AG1 — Control Grid

EIA chart transcription; independent manufacturer verification pending

Unverified

EIA Base Connections, printed page 128, 7CV

PIN6G2AG2 — Screen Grid

EIA chart transcription; independent manufacturer verification pending

Unverified

EIA Base Connections, printed page 128, 7CV

PIN7PAP — Plate (Anode)

EIA chart transcription; independent manufacturer verification pending

Unverified

EIA Base Connections, printed page 128, 7CV

Section ratings

1 physical section, each with unique specifications.

Section 1

Beam Power

X-ray radiationInterelectrode capacitances
Plate resistance
15000 Ω
Transconductance
0.0092 S
Max plate voltage
130 V
Max screen voltage
130 V
Max plate dissipation
5 W
Max screen dissipation
1.4 W

Promoted values are limited to values explicitly present in this supplied 12-V datasheet block; additional published values are retained in parameter rows.

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

1961 Tung Sol

Published operating points and test conditions from this source.

SECTION 1

Beam Power

Other

  • Heater voltage

    12.6 V

    Nominal

  • Heater current

    600 mA

    Nominal

  • Plate voltage

    110125 V

    Typical operating conditions

  • Screen voltage

    110126 V

    Typical operating conditions

  • Plate current

    3237 mA

    Typical operating conditions

Data set 02

1966 Tung Sol Electronic Tubes 2 of 4

Published operating points and test conditions from this source.

SECTION 1

Beam Power

Other

  • Plate voltage

    125 V

    ClassA1

  • Screen voltage

    125 V

    ClassA1

  • Grid 1 voltage

    -4.5 V

    ClassA1

  • Plate current

    37 mA

    ClassA1

  • Signal power output

    1.5 W

    ClassA1

Characteristic

  • Heater warm-up time

    11 s

    WholeTube

Data set 03

1971 RCA HB3 Binder 5 of 7

Published operating points and test conditions from this source.

SECTION 1

Beam Power

Characteristics

  • Voltage

    12.6 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Current

    600 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Warm-up time (Average)

    11

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Grid No.1 to plate

    5

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • grid No. 2, and heater — published value 1

    2

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • grid No. 2, and heater — published value 2

    15

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • grid No. 2, and heater — published value 1

    2

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • grid No. 2, and heater — published value 2

    9

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Pin i-Cathode,

    4

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Grid No.3

    5

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Pin 2 -Grid No.l — published value 1

    2

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Pin 2 -Grid No.l — published value 2

    6

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Pin 3 —Heater — published value 1

    3

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Pin 3 —Heater — published value 2

    7

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Plate Voltage — published value 1

    110 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Plate Voltage — published value 2

    125 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Grid—No.2 Voltage — published value 1

    110 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Grid—No.2 Voltage — published value 2

    125 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Grid—No.l Voltage — published value 1

    4 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Grid—No.l Voltage — published value 2

    4.5 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Peak AF Grid—No.i Voltage — published value 1

    4 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Peak AF Grid—No.i Voltage — published value 2

    4.5 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Zero—Signal Plate Current — published value 1

    32 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Zero—Signal Plate Current — published value 2

    37 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Zero—Signal Grid—No.2 Current — published value 1

    3.5 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Zero—Signal Grid—No.2 Current — published value 2

    4 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Plate Resistance (Approx.) — published value 1

    16000 ohm

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Plate Resistance (Approx.) — published value 2

    15000 ohm

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Transconductance — published value 1

    8100

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Transconductance — published value 2

    9200

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Load Resistance — published value 1

    3500 ohm

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Load Resistance — published value 2

    4500 ohm

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Ep=12.6 VOLTS — published value 1

    12.6 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Ep=12.6 VOLTS — published value 2

    2 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Ep=12.6 VOLTS — published value 3

    125 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • PLATE (Ib)OR GRID-N-'2 (IC2)MILLIAMPE RES

    2 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Eq=12.6 VOLTS PLATE VOLTS=125 — published value 1

    12.6 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Eq=12.6 VOLTS PLATE VOLTS=125 — published value 2

    125 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Eq=12.6 VOLTS PLATE VOLTS=125 — published value 3

    125 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Heater voltage

    12.6 V

    Nominal heater rating

  • Heater current

    600 mA

    Nominal heater rating

Other

  • PLATE VOLTAGE

    130 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • GRID-No.2 (SCREEN) VOLTAGE

    130 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Positive bias value

    0 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • PLATE DISSIPATION

    5 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • GRID-No.2 INPUT — published value 1

    1 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • GRID-No.2 INPUT — published value 2

    4 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Heater negative with respect to cathode

    200 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Heater positive with respect to cathode

    200 V

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Max.—Signal Plate Current — published value 1

    31 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Max.—Signal Plate Current — published value 2

    36 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Max.—Signal Grid—No.2 Current — published value 1

    7.5 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Max.—Signal Grid—No.2 Current — published value 2

    11 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Max.—Signal Power Output — published value 1

    1.1 W

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Max.—Signal Power Output — published value 2

    1.5 W

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • For fixed—bias operation — published value 1

    0 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • For fixed—bias operation — published value 2

    1 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • For cathode—bias operation — published value 1

    0 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • For cathode—bias operation — published value 2

    5 mA

    Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

  • Maximum screen dissipation/input

    1.4 W

    PublishedOn12VSheet

Data set 04

1975 RCA RC30

Published operating points and test conditions from this source.

SECTION 1

Beam Power

Other

  • per Plate 150 200

    240 Ω

    Published in approved 12CA5 target entry; Section1

  • For dc output current of

    150 mA

    Published in approved 12CA5 target entry; Section1

  • For dc output current of 150 mA 245 293

    347 V

    Published in approved 12CA5 target entry; Section1

  • Heater Voltage (ac/dc) 6.3

    126 V

    Published in approved 12CA5 target entry; Section1

  • Heater Current 1.2

    600 mA

    Published in approved 12CA5 target entry; Section1

  • Heater Warm-up Time (Average)

    11 seconds

    Published in approved 12CA5 target entry; Section1

  • Plate Voltage

    130 V

    Published in approved 12CA5 target entry; Section1

  • Grid-No.2 (Screen-Grid) Voltage

    130 V

    Published in approved 12CA5 target entry; Section1

  • Grid-No.l (Control-Grid) Voltage, Positive-bias value

    0 V

    Published in approved 12CA5 target entry; Section1

  • Plate Dissipation

    5 W

    Published in approved 12CA5 target entry; Section1

  • Grid-No. 2 Input

    1.4 W

    Published in approved 12CA5 target entry; Section1

  • Plate Voltage 110

    125 V

    Published in approved 12CA5 target entry; Section1

  • Grid-No.2 Voltage 110

    125 V

    Published in approved 12CA5 target entry; Section1

  • Grid-No.l (Control-Grid) Voltage

    -4.5 V

    Published in approved 12CA5 target entry; Section1

  • Peak AF Grid-No.l Voltage 4

    4.5 V

    Published in approved 12CA5 target entry; Section1

  • Zero-Signal Plate Current 32

    37 mA

    Published in approved 12CA5 target entry; Section1

  • Maximum-Signal Plate Current 31

    36 mA

    Published in approved 12CA5 target entry; Section1

  • Zero-Signal Grid-No.2 Current (Approx.) 3.5

    4 mA

    Published in approved 12CA5 target entry; Section1

  • Maximum-Signal Grid-No.2 Current (Approx.) 7.5

    11 mA

    Published in approved 12CA5 target entry; Section1

  • Plate Resistance (Approx.) 16000

    15000 Ω

    Published in approved 12CA5 target entry; Section1

  • Transconductance 8100

    9200 µS

    Published in approved 12CA5 target entry; Section1

  • Load Resistance 3500

    4500 Ω

    Published in approved 12CA5 target entry; Section1

  • Total Harmonic Distortion 5

    6 %

    Published in approved 12CA5 target entry; Section1

  • Maximum-Signal Power Output 1.1

    1.5 W

    Published in approved 12CA5 target entry; Section1

  • For fixed-bias operation

    0.1 MΩ

    Published in approved 12CA5 target entry; Section1

  • For cathode-bias operation

    0.5 MΩ

    Published in approved 12CA5 target entry; Section1

  • length,

    4 %

    Published in approved 12CA5 target entry; Section1

  • Heater Voltage (ac/dc)

    6.3 V

    Published in approved 12CA5 target entry; Section1

  • Heater Current

    1.5 A

    Published in approved 12CA5 target entry; Section1