5BT8

Indirectly heated double-diode, sharp-cutoff pentode designed for television AFC and detector circuits, IF and video amplification, and automatic gain control. Features a 4.7 V, 600 mA controlled-warm-up heater suitable for series-string operation.

Directly heatedCold cathodeCommon cathodeDissimilar

Sections: 3
Base: -
Socket code: B9A
Base pins: 9
Nominal heater: 4.7 V / 600 mA

Socket description

Small-button Noval 9-contact

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base: -
Socket code: B9A
Base pins: 9
Nominal heater voltage: 4.7 V
Nominal heater current: 600 mA
Parallel heater voltage: -
Parallel heater current: -
Series capable: Yes

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

Diode

X-ray radiationInterelectrode capacitances

No fixed ratings are recorded for this section.

First physical diode in the Sylvania 5BT8 double-diode and sharp-cutoff pentode, used in television AFC/detector applications. Published unshielded diode capacitances (each diode): plate to heater/cathode 1.3 pF; cathode to heater/plate 3.0 pF. Average diode current 8.0 mA at 10 V DC applied is a typical characteristic, not a maximum cathode-current rating. Pentode-to-diode coupling capacitances also specified: pentode grid-1 to diode plate 0.005 pF; pentode plate to diode plate 0.020 pF. Separate physical diode section; no maximum ratings inferred from operating point.

Section 2

Diode

X-ray radiationInterelectrode capacitances

No fixed ratings are recorded for this section.

Second physical diode in the Sylvania 5BT8 double-diode and sharp-cutoff pentode, used in television AFC/detector applications. Published unshielded diode capacitances (each diode): plate to heater/cathode 1.3 pF; cathode to heater/plate 3.0 pF. Average diode current 8.0 mA with 10 V DC applied is a typical characteristic, not a maximum cathode-current rating. Pentode grid-1 to diode plate coupling 0.005 pF and pentode plate to diode plate coupling 0.020 pF. This is a distinct physical diode section; no independent maximum rating is inferred.

Section 3

Pentode

X-ray radiationInterelectrode capacitances

Plate resistance: 300000 Ω
Transconductance: 0.0062 S
Max plate voltage: 300 V
Max plate dissipation: 2 W
Max screen dissipation: 0.5 W

Sylvania 5BT8 indirectly heated sharp-cutoff pentode plus two physical diodes. Pentode service: IF, video, AGC amplification or reactance tube in television receivers; double diodes serve AFC and detector functions. Heater 4.7 V 600 mA with approximately 11-second controlled warm-up suitable for series-string operation. Small-button nine-pin miniature base E9-1, manufacturer basing 9FE (parent general socket family B9A). Manufacturer design-center maximum plate voltage 300 V, plate dissipation 2.0 W, grid-2 input 0.5 W. Grid-2 SUPPLY maximum 300 V does not establish an unrestricted screen-electrode maximum: grid-2 voltage subject to separate rating chart, so max_screen_voltage retained NULL. Typical pentode operating conditions at Va 200 V, grid-2 150 V, cathode resistor 180 ohms: Ia 9.5 mA, Ig2 2.8 mA, transconductance 6200 µmhos (0.0062 S), plate resistance about 300 kΩ, approximate cutoff bias -8 V. Published unshielded pentode capacitances grid-1 to plate max 0.04 pF, input 7.0 pF, output 2.3 pF; each diode plate-to-(heater+cathode) 1.3 pF, cathode-to-(heater+plate) 3.0 pF; cross-section coupling pentode grid-1 to diode plate 0.005 pF, pentode plate to diode plate 0.020 pF. Typical values not promoted as maximums.

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

1970 Sylvania Technical Manual

Published operating points and test conditions from this source.

SECTION 3

Pentode

Characteristics

Plate Voltage
200 V
Screen Voltage
125 V