MHD4

Early double-diode triode combining receiver detection, automatic volume control, and low-level amplification. Two diode sections provide signal and control-voltage rectification while the triode supplies the associated amplifier stage.

Directly heatedCold cathodeCommon cathodeDissimilar

Sections: 3
Base: -
Socket code: B7
Base pins: 7
Nominal heater: 4 V / 1 A

Description

OSRAM MHD4 double-diode triode for detection, automatic volume control, and amplification.

Socket description

Medium 7-contact

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base: -
Socket code: B7
Base pins: 7
Nominal heater voltage: 4 V
Nominal heater current: 1 A
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

3 physical sections, each with unique specifications.

Section 1

Triode

X-ray radiationInterelectrode capacitances

Plate resistance: 18200 Ω
Transconductance: 0.0022 S
Amplification factor: 40
Max plate voltage: 250 V

Representative triode section; diode data retained as parameters. Osram MHD4 indirectly heated 4 V, 1 A double-diode triode for receiver detection, automatic volume control and low-frequency amplification. Triode maximum plate voltage 250 V; characteristic constants amplification factor 40, internal resistance 18.2 kΩ and transconductance 2.2 mA/V, measured at 100 V anode and zero grid bias. Two detector diodes share its common cathode.

Section 2

Diode

X-ray radiationInterelectrode capacitances

No fixed ratings are recorded for this section.

Physical diode section added during approved section-structure reconciliation. First physical diode of Osram MHD4; used for receiver detection. May combine with second diode for full-wave rectification. Common cathode shared with other two electrode sections.

Section 3

Diode

X-ray radiationInterelectrode capacitances

No fixed ratings are recorded for this section.

Physical diode section added during approved section-structure reconciliation. Second physical diode of the Osram MHD4 double-diode triode. The second diode may serve automatic volume control using a separate circuit, or combine with the first diode for full-wave signal rectification. Both diodes share the common cathode and cathode-connected shield.

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

1955 Marconi

Published operating points and test conditions from this source.

SECTION 1

Triode

Capacitance

Anode-grid capacitance
3.8 pF
Grid-earth capacitance
2.4 pF
Anode-earth capacitance
4.7 pF
Grid-each-diode capacitance
0.15 pF
Diodes-earth capacitance
12.7 pF

Construction

Physical diode count
2
Physical triode count
1

Other

Typical HT voltage
250 V