KT120

Beam Tetrode — Octal

Tung-Sol

Known Equivalents & Substitutes

No known equivalents. If you know of any, use the ⚑ Report Issue button above.

Similar Tubes (Not Drop-In Compatible)

Same Octal base beam tetrode but KT120 has much higher ratings (Pa_max 60W vs 35W). Same pin functions but different operating points and heater current.

KT88

Same Octal base beam tetrode family but KT120 has significantly higher ratings (Pa_max 60W vs 42W, different bias requirements). Not a drop-in — requires circuit adjustment for higher heater current and different operating points.

Electrical Specifications

Section 1 — Beam Tetrode

Absolute Maximum

Anode Voltage (max)Anode Voltage (max, tetrode)850V

Screen Voltage (max)Screen Voltage (max, pentode)650V

Anode Dissipation (max)Anode Dissipation (max)60W

Screen Dissipation (max)Screen Dissipation (max)8W

Cathode Current (max)Cathode Current (max, pentode)

Section 2 — Triode Strapped

Absolute Maximum

Anode Voltage (max)Anode Voltage (max, triode)650V

Anode Dissipation (max)Anode Dissipation (max)60W

Cathode Current (max)Cathode Current (max, triode/UL)230mA

Max Grid ResistorMax Grid Resistor (self-bias)0.24MΩ

Typical Operating

Heater

Heater VoltageHeater Voltage6.3V

Heater CurrentHeater Current1.8A

Notes

Rg_max depends on bias method: fixed bias 51 kΩ, self (cathode) bias 240 kΩ.
Vhk_max is asymmetric: 300 V with heater negative w.r.t. cathode, 200 V with heater positive w.r.t. cathode.
Maximum ratings differ between tetrode and triode/UL modes: Va_max tetrode = 850 V, Va_max triode = 650 V; Vg2_max pentode = 650 V, Vg2_max triode/UL = 600 V; Ik_max pentode = 250 mA, Ik_max triode/UL = 230 mA.
Pin 1 is the outer metal screen (internal shield), not a beam plate connection. Pin 8 is cathode tied to the beam-forming screen internally.
The KT120 is physically larger than a KT88 (52 mm diameter, 130 mm seated height) — verify clearance before substitution.
Triode-strapped data sourced from Turner Audio measured Ra curves (https://www.turneraudio.com.au/loadmatch-1-SE-triodes.html), not from the manufacturer datasheet. The Tung-Sol datasheet provides triode max ratings but no triode operating point or small-signal parameters.

Pin Layout — Octal

1Outer Metal Screen (internal shield)

2Heater

3Anode (Plate)

Socket-Compatible Tubes ⚠ Not electrically compatible

6L6 KT150 KT170 KT63

References