EL34EH Paar matched tubes EHX Röhren Premium matched Pair

Electro-Harmonix EL34EH – BTB-matched output-valve pair for push-pull amplifiers

This set contains two current-production Electro-Harmonix EL34EH valves. The indirectly heated power pentode uses an eight-pin octal base, a nominal 6.3 V heater supply and a maximum plate-dissipation rating of 25 W. Typical applications include compatible hi-fi, guitar and studio power amplifiers using two EL34 valves in push-pull operation.

BTB selects the two valves as one Premium matched pair at a practical plate voltage of 450 V. The set is particularly suitable for output stages using exactly two EL34 valves together. An amplifier using four output valves should preferably be fitted with one quad matched as a complete group.

Suitable applications

• Push-pull guitar amplifiers using a total of two EL34 output valves
• Hi-fi and studio power amplifiers using one EL34 pair per channel or mono stage
• Stereo single-ended amplifiers using one EL34 per identically configured channel
• Complete replacement of an existing two-valve output set
• New builds with a suitable heater supply, screen-grid circuit and output transformer
• Circuits explicitly designed for an EL34 or a manufacturer-approved 6CA7 alternative

BTB Premium Matching

Package contents

Two Electro-Harmonix EL34EH valves

Selection type

BTB Premium matched pair

Practical matching plate voltage

450 V unless the specific product states otherwise

BTB baseline-measurement example

450 V plate voltage, approximately -40 V control-grid voltage and approximately 40 mA plate current

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 the two push-pull halves

Technical data

Valve type

Indirectly heated power pentode

Type designation

EL34EH

Manufacturer classification

Electro-Harmonix identifies the EL34EH as an EL34 and 6CA7-equivalent audio output valve

Base

Eight-pin octal K8A

Nominal heater voltage

6.3 V

Heater current

1.35 to 1.65 A per valve; approximately 1.5 A nominal

Heater current for the pair

Up to 3.3 A at 6.3 V

Data-sheet test point

250 V plate voltage, 265 V screen-grid voltage and -13.5 V control-grid voltage

Plate current at the test point

80 to 120 mA

Screen-grid current at the test point

10 to 20 mA

Transconductance at the test point

9.5 to 15 mA/V

Single-ended output example

At least 8.5 W into a 2 kΩ plate load under the stated data-sheet conditions; not an output rating for the pair in a push-pull amplifier

Maximum plate dissipation

25 W per valve

Maximum screen-grid dissipation

8 W per valve according to the current production sheet

Maximum cathode current

150 mA per valve

Heater-to-cathode voltage

Maximum ±100 V in the current production sheet; an older official EHX sheet states ±200 V

Maximum envelope temperature

523 K, approximately 250 °C

Dimensions

Approx. 111 ±2 mm overall height and approximately 31 to 32 mm envelope diameter

Production type

Current production

Country of origin

Russia according to current BTB and manufacturer information

Pinout

Pin 1

Suppressor grid g3

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

Comparison with 6CA7, KT77 and four-valve sets

EL34EH

Classic power pentode with the suppressor grid brought out internally to pin 1

6CA7

Identified by Electro-Harmonix as a related equivalent type. Internal construction and the use of pin 1 can differ between versions

KT77

Related octal output valve with different curves and potentially different limits; use only where approved

Matched quad

Technically preferable for an amplifier using four EL34 valves together rather than two independently assembled pairs

Selection and application notes

Matching does not replace bias adjustment. In a fixed-bias amplifier, check and adjust the quiescent currents after installation. In a cathode-biased circuit, verify the cathode voltage, plate dissipation and heater voltage under normal operating conditions.

Pin 1 is connected to the suppressor grid in the EL34EH. It must not be treated as a free tie point without checking. Inspect the socket wiring before replacing a 6CA7, KT77 or another octal output-valve type.

The comparatively high transconductance requires short signal paths, suitable control-grid and screen-grid stopper resistors and effective power-supply decoupling. An unsuitable layout can otherwise permit unwanted radio-frequency oscillation.

BTB subjectively describes the EL34EH in terms of warm midrange and a harmonically balanced character, while Electro-Harmonix describes a smooth and detailed presentation. The audible result also depends on bias, the output transformer, feedback, loudspeaker and power supply.

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

Questions about selection and use

Is the Electro-Harmonix EL34EH Premium matched pair suitable for a push-pull output stage using two EL34 valves?

Yes, the Electro-Harmonix EL34EH Premium matched pair is suitable for compatible push-pull output stages using a total of two EL34 valves. The heater supply, plate and screen-grid voltages, bias range, output transformer and socket wiring must suit the specific amplifier.

Can the EL34EH pair replace an existing two-valve EL34 or 6CA7 set?

Yes, the EL34EH pair can replace an existing two-valve EL34 set and many applications approved for EL34 or 6CA7 valves. Pin 1, heater demand, bias range and the screen-grid circuit require particular verification before substitution.

Should the bias be checked after installing the matched EL34EH pair?

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