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Power - Triode ·Triode-Triode

33AI38A

Twin power triode with identical sections usable in parallel or push-pull audio and RF stages. Published conditions cover Class A and Class B audio output as well as Class C transmitting service around 14 W.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
2
Base
-
Socket code
MEDIUM7
Base pins
7
Nominal heater
6.3 V / 800 mA

Description

Twin triode with two identical sections for audio- and radio-frequency power-amplifier service.

Socket description

Medium 7-contact transmitting-tube base

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
-
Socket code
MEDIUM7
Base pins
7
Nominal heater voltage
6.3 V
Nominal heater current
800 mA
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

2 physical sections, each with unique specifications.

Section 1

Triode

X-ray radiationInterelectrode capacitances
Plate resistance
4700 Ω
Transconductance
0.0029787234042553193 S
Amplification factor
14
Max plate voltage
300 V
Max plate dissipation
5 W
Max cathode current
50 mA

Representative row for two electrically identical triode sections.

Section 2

Triode

X-ray radiationInterelectrode capacitances
Plate resistance
4700 Ω
Transconductance
0.0029787234042553193 S
Amplification factor
14
Max plate voltage
300 V
Max plate dissipation
5 W
Max cathode current
50 mA

Identical second physical section; duplicated from representative section per physical-section-row policy.

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

1947 Standard Valves

Published operating points and test conditions from this source.

SECTION 1

Triode

Capacitance

  • GridToAnodeCapacitance

    2.7 pF

  • GridToCathodeOrFilamentCapacitance

    6 pF

  • AnodeToCathodeOrFilamentCapacitance

    1.3 pF

Other

  • Typical Plate Voltage

    300 V

    ClassA TwoSectionsParallel

  • Grid Bias

    -13 V

    ClassA TwoSectionsParallel

  • Plate Current

    30 mA

    ClassA TwoSectionsParallel

  • Power Output

    1 W

    ClassA TwoSectionsParallel

  • Power Output

    1.2 W

    ClassA PushPull

  • Power Output

    12 W

    ClassB PushPull TwoSections

  • Power Output

    14 W

    ClassC RF PushPull

  • MaximumFrequencyForFullRatings

    100 MHz

  • MaximumOperatingFrequency

    300 MHz