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PL81 — Power Pentode, Noval | Tubeofile | Tubeofile

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PL81

Name: PL81
Brand: Philips

Power Pentode — Noval — Philips

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Data: HighHigh quality — base, heater, all universal parameters present, and ≥50% of desirable parameters filled in. Safe to use for design decisions.

↗ TDSL ↗ Radiomuseum

Known Equivalents & Substitutes

21A6

Similar Tubes (Not Drop-In Compatible)

EL44

Listed as equivalent in Brans — B8A base, 6.3V heater, not pin-compatible

EL81

Same electrical characteristics but 6.3V/1.05A parallel heater — not a drop-in in 300mA series-string circuits

Electrical Specifications

Section 1 — Pentode

Absolute Maximum

Anode Voltage (max)Anode Voltage (max)250V

Screen Voltage (max)Screen Voltage (max)250V

Anode Dissipation (max)Anode Dissipation (max)8W

Screen Dissipation (max)Screen Dissipation (max)4.5W

Notes

300mA series-string heater (21.5V/0.3A) for AC/DC TV receivers. The 'P' prefix in Mullard/Philips nomenclature denotes a 300mA heater string design.
Philips interchange lists 21A6 as the American equivalent designation. CV5077.
Brans Vademecum lists EL44 as equivalent — this is a B8A-base tube, not pin-compatible with PL81's Noval base.
Electrically identical to EL81 in all electrode characteristics; only the heater differs.
Not interchangeable with EL81 without heater circuit modification.

Pin Layout — Noval

1Cathode

2Control Grid (g1)

3Heater

Socket-Compatible Tubes ⚠ Not electrically compatible

AL860 EL81

References

https://tdsl.duncanamps.com/show.php?des=PL81
https://www.radiomuseum.org/tubes/?tube=PL81

Cathode Current (max)

180mA

Heater-to-Cathode Voltage (max)Heater-to-Cathode Voltage (max)100V

Max Grid ResistorMax Grid 1 Resistor0.5MΩ

Typical Operating

Anode Voltage (typical)Anode Voltage (typical)250V

Screen Voltage (typical)Screen Voltage (typical)250V

Grid 1 Bias VoltageGrid 1 Bias Voltage-38.5V

Anode CurrentAnode Current32mA

Screen CurrentScreen Current2.4mA

Anode ResistanceAnode Resistance15,000Ω

TransconductanceTransconductance4.6mA/V

Output

Output PowerOutput Power3.3W

Load ImpedanceLoad Impedance7,800Ω

Capacitances

Grid-to-Plate CapacitanceAnode to Grid 1 Capacitance0.8pF

Anode-to-Cathode CapacitanceAnode-to-Cathode Capacitance0.1pF

Input CapacitanceInput Capacitance (g1 to all except anode)14pF

Output CapacitanceOutput Capacitance (anode to all except g1)6pF

Section 2 — Triode Strapped

Absolute Maximum

Anode Voltage (max)Anode Voltage (max)250V

Anode Dissipation (max)Anode Dissipation (max)8W

Cathode Current (max)Cathode Current (max)180mA

Typical Operating

Anode Voltage (typical)Anode Voltage250V

Grid 1 Bias VoltageGrid 1 Bias Voltage-38V

Anode CurrentAnode Current40mA

Anode ResistanceAnode Resistance1,000Ω

TransconductanceTransconductance5.5mA/V

Amplification Factor (μ)Amplification Factor (μ)5.5—

Heater

Heater VoltageHeater Voltage22V

Heater CurrentHeater Current0.3A

4Heater

5Screen Grid (g2)

6Anode

7Internal Connection

8Internal Connection

9Suppressor Grid (g3)