3B4 (=DL98) Pentode
€4.40
Delivery time: ca. 1 - 5 days
Used in portable tube radios and small audio amps
Popular for DIY hifi mini amplifier projects
Low heater current, B7G base, ideal for battery use
3B4 / DL98 battery pentode for compact audio power stages
The 3B4, also known as the DL98, is a directly heated B7G beam-power pentode designed for portable battery equipment. Its selectable 1.25/2.5 V filament and approximately 3 W plate-dissipation rating make it an unusual candidate for experimental low-power audio amplifiers.
It may be explored in either single-ended or two-valve push-pull circuits. Published reference data mainly covers RF Class-C operation, so an audio circuit requires a newly calculated operating point and output transformer.
Useful applications
- Compact battery-powered mono and stereo amplifiers
- Experimental single-ended output stages
- Affordable push-pull amplifier projects
- Portable valve equipment and vintage service
Technical specifications
- Valve type
- Directly heated beam-power pentode
- Equivalent designations
- DL98, CV2240 and HD30
- Base
- Miniature B7G, 7-pin
- Filament
- 2.5 V at 165 mA or 1.25 V at 330 mA using the centre tap
- Published Class-C condition
- Va 150 V, Vg2 135 V, Vg1 approximately −39 V, Ia 25 mA and Ig2 6.2 mA
- Transconductance
- Approximately 1.7 mA/V under the published Class-C condition
- Maximum anode voltage
- Approximately 200 V in published valve data
- Maximum anode dissipation
- Approximately 3 W
- Dimensions
- Approximately 18 mm in diameter and 47 mm body height excluding pins
B7G connections – bottom view
- Pin 1
- Screen grid g2
- Pins 2 and 6
- Filament centre tap, beam plates and shield
- Pin 3
- Control grid g1
- Pins 4 and 5
- Filament ends
- Pin 7
- Anode
Audio design notes
Direct heating requires careful filament, grounding and bias arrangements to control hum. A battery can power the filament, but the anode circuit still requires a suitable high-voltage battery or low-noise converter.
Safety notice: A battery-powered valve amplifier may still contain lethal anode voltages.
Questions about selection and audio use
Is the 3B4 / DL98 suitable for a compact battery audio amplifier?
Yes, its directly heated 1.25/2.5 V filament and useful miniature power rating make it attractive for portable low-power amplifiers. The audio operating point and output transformer must be calculated from the valve characteristics.
Can two 3B4 valves be used in a push-pull output stage?
Yes, two closely performing valves can be used in a custom push-pull circuit. The transformer impedance, idle current, bias and screen supply must be developed specifically for the intended amplifier.
Can the 3B4 be operated from batteries or rechargeable cells?
Yes, its filament can operate at 1.25 V and 330 mA or 2.5 V and 165 mA. A separate high-voltage battery or suitably filtered converter is still required for the anode supply.
Note: All brand names mentioned, such as Marshall, Fender, etc., are registered trademarks of their respective owners and are used here for descriptive and compatibility purposes only.
Antiquität Hersteller geschlossen
oder unbekannt
The EU Directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment (2011/65/EU = "RoHS 2") aims to exclude certain hazardous substances from electrical and electronic equipment or to restrict the use of certain substances in electrical and electronic equipment. These include substances such as lead, mercury, cadmium, and chromium, as well as certain brominated flame retardants and plasticizers. These substances may only be used in electrical and electronic equipment up to a maximum concentration limit, unless exemptions in the annexes to the directive permit their use under certain conditions. This can reduce and eliminate harmful substances and improve the recycling of waste electrical and electronic equipment. To find out whether the component you purchased from us is permitted in your device, please refer to the current directive or the current law applicable to your country. If you are a manufacturer, please feel free to contact us to find out whether the component you require can be tested and approved according to the current directives. We would be happy to assist you.
Fact sheet on EU Directive 2011/65/EURestriction of the use of hazardous substances in electrical and electronic equipment (PDF, not accessible, 2 MB)
Source: IHK Mittelfranken
Tariff Number: 85408100900
Country of Origin: DE