KT90

Beam Tetrode — Octal

Known Equivalents & Substitutes

Electrical Specifications

Section 1 — Beam Tetrode

Absolute Maximum

Anode Voltage (max)Anode Voltage (max)750V

Screen Voltage (max)Screen Voltage (max)650V

Anode Dissipation (max)Anode Dissipation (max)50W

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

Cathode Current (max)Cathode Current (max)230mA

Heater-to-Cathode Voltage (max)Heater-to-Cathode Voltage (max)300V

Typical Operating

Anode Voltage (typical)Anode Voltage250V

Screen Voltage (typical)Screen Voltage250V

Grid 1 Bias VoltageGrid 1 Bias Voltage-14V

Anode CurrentAnode Current145mA

Screen CurrentScreen Current

Capacitances

Grid-to-Plate CapacitanceGrid-to-Plate Capacitance1.8pF

Input CapacitanceInput Capacitance29pF

Output CapacitanceOutput Capacitance10pF

other

Pa+Pg2 (max combined)Pa+Pg2 (max combined)54W

Vg1 cutoff (Ia ≈ 1 mA)Vg1 cutoff (Ia ≈ 1 mA)-36V

Section 2 — Triode Strapped

Absolute Maximum

Anode Voltage (max)Anode Voltage (max, triode)600V

Anode Dissipation (max)Anode Dissipation (max)50W

Cathode Current (max)Cathode Current (max)230mA

Typical Operating

Anode Voltage (typical)Anode Voltage (Va = Vg2)250V

Heater

Heater VoltageHeater Voltage6.3V

Heater CurrentHeater Current1.6A

Notes

The EI datasheet does not provide single-ended load impedance (rl) or single-ended output power (Pout). Only push-pull figures are given: 110 W/pair at Va=550 V, Vg2=400 V; 160 W/pair at Va=750 V, Vg2=600 V.
TDSL lists additional substitutes with different ratings: 6550B, 6550C, CK6550, CV5220, KT88S, KT88SC, SV6550C.
Pin 1 has no connection. Pin 6 has no connection. Pin 8 is cathode tied to beam-forming plates internally.
Vhk_max (heater-to-cathode voltage) is 300 V total DC — higher than many octal power tubes.
Triode-strapped data is from the manufacturer datasheet (EI). Schlangen (2009) independently measured similar values: mu=9.0, gm=15.0 mA/V, rp=700 Ohm at Va=650 V, Ik=600 mA max.

Pin Layout — Octal

1No Connection

2Heater

3Anode

Socket-Compatible Tubes ⚠ Not electrically compatible

References