KT66 Genalex GoldLion tube Röhren BTB matched Pair

Genalex Gold Lion KT66 – BTB-matched pair for push-pull amplifiers

This set contains two current-production Genalex Gold Lion KT66 valves. The indirectly heated beam tetrode uses an eight-pin octal base, a nominal 6.3 V heater and carries a maximum plate-dissipation rating of 25 W.

BTB matches both output valves at a practical plate voltage of 450 V. The pair is suitable for compatible push-pull stages using two KT66 valves or two identically configured single-ended channels. An amplifier using four KT66 valves should preferably use one matched quad.

Suitable applications

• Guitar amplifiers explicitly designed for two KT66 output valves
• Hi-fi push-pull output stages using one KT66 pair
• Stereo single-ended amplifiers using one KT66 per channel
• Complete replacement of an existing two-valve KT66 set
• New builds with an adequately rated heater supply and suitable output transformer
• Professionally verified conversion of compatible 6L6 circuits after checking heater demand, bias and clearance

BTB matching and package contents

Package contents

Two Genalex Gold Lion KT66 valves

Selection type

BTB-matched pair

Matching plate voltage

A practical 450 V unless the specific product states otherwise

Test system

Roetest V11, current as of 2026

Parameters considered

Plate current, transconductance, grid currents, plate resistance and acoustic checks

Technical benefit

Closely corresponding quiescent currents and characteristics in both output valves

Technical data

Valve type

Indirectly heated beam power tetrode

Type designation

KT66 Genalex Gold Lion

Base

Eight-pin octal

Nominal heater voltage

6.3 V

Heater current

1.3 to 1.6 A per valve

Heater current for the pair

Up to 3.2 A at 6.3 V

Data-sheet test point

250 V plate and screen-grid voltage with -15 V control-grid voltage

Plate current at the test point

60 to 110 mA

Screen-grid current at the test point

10 mA maximum

Transconductance at the test point

5 mA/V minimum

Single-ended output example

At least 5.4 W into a 2.2 kΩ plate load under the stated conditions

Maximum plate dissipation

25 W per valve

Maximum screen-grid dissipation

3.5 W per valve

Maximum cathode current

200 mA per valve

Dimensions

Approximately 122 mm overall height and up to about 53 mm envelope diameter

Country of origin

Russia according to current BTB and manufacturer information

Pinout

Pin 1

No electrode connection

Pins 2 and 7

Heater

Pin 3

Plate

Pin 4

Screen grid g2

Pin 5

Control grid g1

Pin 6

No internal electrode connection

Pin 8

Cathode and beam-forming plates

Comparison with 6L6GC and 5881

KT66

Large beam tetrode with greater heater demand and its own characteristic curves

6L6GC

Related octal output valve, but not interchangeable in every amplifier without checking bias, heater reserve and clearance

5881

Related member of the 6L6 family with potentially lower dissipation and different voltage limits

Selection and application notes

Matching does not replace bias adjustment. Check the quiescent current and plate dissipation of each valve after installation. In cathode-biased circuits, verify cathode voltage and total current as well.

Heater current can be substantially greater than that of a 6L6GC or 5881. The power transformer, fuse, wiring and sockets must provide up to 3.2 A for the pair.

The larger envelope requires sufficient clearance to the cover, retainers, adjacent valves and heat-sensitive components.

Power valves become very hot and operate with lethal voltages. Replace and bias them only with the equipment disconnected, discharged and cool.

Questions about selection and use

Is the Genalex Gold Lion KT66 BTB-matched pair suitable for a push-pull stage using two KT66 valves?

Yes, the Genalex Gold Lion KT66 BTB-matched pair is suitable for compatible push-pull output stages using a total of two KT66 valves. The heater supply, plate and screen-grid voltages, bias range, output transformer and clearance must suit the circuit.

Can the KT66 pair replace an existing KT66 or approved 6L6 set?

Yes, the KT66 pair can replace an existing KT66 set and 6L6 applications explicitly approved by the equipment manufacturer. Heater demand, bias, socket wiring and physical height require particular verification before conversion.

Should the bias and heater supply be checked after installing the matched KT66 pair?

Yes, the bias or quiescent current and heater voltage must be checked after installation. BTB matching supports closely corresponding valve values but does not replace adjustment for the actual operating voltage and amplifier circuit.