KT77

Name: KT77
Brand: GEC

Beam Tetrode — Octal — GEC

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

↗ r-type.org ↗ TDSL ↗ Radiomuseum

Known Equivalents & Substitutes

6CA7

Similar Tubes (Not Drop-In Compatible)

EL34

Same Octal pinout and similar ratings but EL34 is a true pentode (pin 1 = suppressor grid) vs KT77 beam tetrode (pin 1 = NC) — different internal topology

Electrical Specifications

Section 1 — Beam Tetrode

Absolute Maximum

Anode Voltage (max)Anode Voltage (max, design)800V

Screen Voltage (max)Screen Voltage (max, design)600V

Anode Dissipation (max)Anode Dissipation (max, design)25W

Screen Dissipation (max)Screen Dissipation (max)6W

Notes

The KT77 is a beam tetrode (internal beam plates connected to cathode at pin 8), unlike the EL34 which is a true pentode with a suppressor grid on pin 1. Pin 1 on the KT77 is No Connection.
GEC specifies ultra-linear connection as the recommended operating mode. Tetrode connection is possible but the fixed screen supply must not exceed 300 V.
Max grid resistor depends on both bias method and dissipation: cathode bias Pa+g2 < 28 W = 1.0 MΩ, > 28 W = 0.5 MΩ; fixed bias Pa+g2 < 28 W = 0.5 MΩ, > 28 W = 0.25 MΩ.
Triode-strapped data from GEC datasheet measured at Va,g2 = 250 V with g2 connected to anode.

Pin Layout — Octal

1No Connection

2Heater

3Anode

4

Socket-Compatible Tubes ⚠ Not electrically compatible

12AV5 12AX4 12DQ6 12E1 12J5 12J5GT 12W6GT 1H4 25L6GT 350B 367A 5881 6550 6A5G 6C2C

References