UCL81 Triode Pentode Allstrom Endstufen Röhre
€3.95
Delivery time: ca. 1 - 5 days
AF output tube with driver triode
Used in 1960s table receivers
Noval B9A; Uf 50V; If 0.1A; Pa~7W
UCL81 triode-output pentode for compact budget amplifiers
The UCL81 combines a preamplifier triode and an audio output pentode in one Noval valve. Its electrode system and pin connections correspond closely to the ECL81, but it uses a 39 V, 100 mA series heater. This makes it an appealing sleeper tube for affordable one-valve amplifiers.
The triode can provide input gain while the pentode drives a suitable output transformer. The documented operating condition provides approximately 2.4 W of audio output.
Suitable applications
- Compact single-ended mono amplifiers
- Affordable desktop and workshop amplifiers
- Small guitar practice amplifiers
- Service of equipment designed for the UCL81
Technical specifications
- Valve construction
- Preamplifier triode and audio output pentode with a common cathode
- Related valve
- Electrode system and pin arrangement correspond to the ECL81, with a different heater
- Base
- Noval B9A, 9-pin
- Heater
- 39 V at 100 mA for series-heater operation
- Triode reference condition
- Va 170 V, Vg −1.5 V, Ia 1.3 mA and approximately 1.6 mA/V transconductance
- Pentode reference condition
- Va 200 V, Vg2 200 V, Vg1 approximately −7 V, Ia 30 mA and Ig2 4.8 mA
- Pentode transconductance
- Approximately 8.75 mA/V
- Typical output power
- Approximately 2.4 W at 10% distortion under the reference conditions
- Maximum pentode anode dissipation
- 6.5 W
- Maximum triode anode dissipation
- 1 W
- Dimensions
- Approximately 20 mm in diameter and 70 mm body length excluding pins
B9A connections – bottom view
- Pin 1
- Triode control grid
- Pin 2
- Pentode screen grid g2
- Pins 3 and 8
- Common cathode and suppressor grid g3
- Pins 4 and 5
- Heater
- Pin 6
- Pentode anode
- Pin 7
- Triode anode
- Pin 9
- Pentode control grid g1
Notes for budget amplifier projects
The triode and pentode share a cathode, which must be considered when selecting bias and feedback arrangements. A correctly specified output transformer is required for loudspeaker operation.
A modern DIY amplifier should use fully isolated heater and high-voltage supplies. Historical transformerless mains circuits should not be copied into a new audio build.
Questions about selection and audio use
Is the UCL81 suitable for an affordable one-valve amplifier?
Yes, its integrated triode can provide the input gain while the pentode operates as a compact single-ended output stage. With a suitable output transformer, one UCL81 can form a mono amplifier delivering approximately 2.4 W under the published reference conditions.
Can the UCL81 be used with ECL81 circuit concepts?
Yes, the triode and pentode systems and the B9A pin arrangement correspond to the ECL81. The heater supply must be changed to 39 V at 100 mA, and the operating point and common cathode must be considered in the final circuit.
Can one UCL81 provide both preamp and output stages?
Yes, this is the main attraction of the compound valve. The triode supplies voltage gain and the pentode drives the loudspeaker through an output transformer, reducing the number of valves and sockets required for a compact budget build.
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.
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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