DF703

Telefunken directly heated subminiature electrometer pentode designed for circuits measuring extremely small grid currents. Its defining role is ultra-high-impedance instrumentation rather than conventional audio or RF amplification.

Directly heatedCold cathodeCommon cathodeDissimilar

Sections: 1
Base: -
Socket code: WIRE8
Base pins: 8
Nominal heater: 1.25 V / 10 mA

Description

The Telefunken DF703 is a directly heated subminiature electrometer pentode designed for extremely low grid-current measurement circuits.

Socket description

Subminiature all-glass 8-wire lead family

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base: -
Socket code: WIRE8
Base pins: 8
Nominal heater voltage: 1.25 V
Nominal heater current: 10 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

1 physical section, each with unique specifications.

Section 1

Pentode

X-ray radiationInterelectrode capacitances

Max plate voltage: 22.5 V
Max screen voltage: 22.5 V
Max cathode current: 0.3 mA

Electrometer pentode.

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

1959 Telefunken

Published operating points and test conditions from this source.

SECTION 1

Pentode

Characteristics

Combined Plate+Screen Current
0.2 mA
TriodeConnection
Triode-Connected Transconductance
175 uS
TriodeConnection
Triode-Connected Amplification Factor
1.8 ratio
TriodeConnection
Maximum Grid Current
0.0000000025 mA
Grid-to-Plate Capacitance
0.05 pF