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4L20 — Power Pentode, Loctal | Tubeofile
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4L20
Power Pentode — DHT — Loctal
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Tesla (Czechoslovakia)
Data: High
High quality — base, heater, all universal parameters present, and ≥50% of desirable parameters filled in. Safe to use for design decisions.
↗ Radiomuseum
Known Equivalents & Substitutes
4P1L
4П1Л
4L1S
4LS1
4P6
RL2,4P6
Similar Tubes (Not Drop-In Compatible)
AL860
East German DHT pentode with similar specs but different base (Noval B9A) and heater voltage (4.8V)
Electrical Specifications
Section 1 — Pentode
Absolute Maximum
Anode Voltage (max)
Maximum Anode Voltage
250
V
Screen Voltage (max)
Maximum Screen Voltage
250
V
Anode Dissipation (max)
Maximum Anode Dissipation
7.5
W
Screen Dissipation (max)
Maximum Screen Dissipation
1.5
W
Notes
Tesla designation for the same tube as 4P1L and the Wehrmacht RL2,4P6. Pin-for-pin drop-in replacement.
DHT with centre-tapped thoriated tungsten filament: 2.1V @ 650mA (parallel) or 4.2V @ 325mA (series).
In triode-strapped mode (g2 tied to anode): mu≈10, ra≈1.6kΩ, gm≈6 mA/V.
Commonly found in audiophile single-ended triode-connected output stages.
Pin Layout — Loctal
1
2
3
4
5
6
7
8
1
Filament
2
Suppressor Grid (g3)
3
Control Grid (g1)
4
References
https://www.radiomuseum.org/tubes/tube_4l20_tesla.html
https://en.uraltone.com/4p1l-4l1s-4ls1-rl2-4p6-audiophile-pentode.html
Cathode Current (max)
Maximum Cathode Current
50
mA
Typical Operating
Anode Voltage (typical)
Anode Voltage
200
V
Screen Voltage (typical)
Screen Voltage
150
V
Grid 1 Bias Voltage
Control Grid Voltage
-7
V
Anode Current
Anode Current
35
mA
Anode Resistance
Internal Plate Resistance
30,000
Ω
Transconductance
Transconductance
6
mA/V
Output
Output Power
Output Power
4.2
W
Capacitances
Grid-to-Plate Capacitance
Grid-to-Anode Capacitance
0.1
pF
Input Capacitance
Input Capacitance
9
pF
Output Capacitance
Output Capacitance
9
pF
Section 2 — Triode Strapped
Absolute Maximum
Anode Dissipation (max)
Maximum Anode Dissipation
7.5
W
Typical Operating
Anode Voltage (typical)
Anode Voltage
235
V
Grid 1 Bias Voltage
Control Grid Voltage
-18
V
Anode Current
Anode Current
40
mA
Anode Resistance
Internal Plate Resistance
1,600
Ω
Transconductance
Transconductance
6
mA/V
Amplification Factor (μ)
Amplification Factor
10
—
Output
Output Power
Output Power
2.5
W
Load Impedance
Load Resistance
5,000
Ω
Heater
Heater Voltage
Heater Voltage
2.1
V
Heater Current
Heater Current
0.65
A
Screen Grid (g2)
5
Anode
6
No Connection
7
Filament
8
Filament Centre Tap