300B EHX Electro Harmonix Gold Röhren factory matched Pair

Electro-Harmonix 300B Gold – factory-matched pair with gold grid wire

This set contains two current-production, directly heated Electro-Harmonix 300B Gold power triodes. The valves use a four-pin UX4 base, a nominal 5 V filament supply and are intended for correctly designed 300B audio output stages.

Electro-Harmonix describes the Gold version as the premium form of the regular 300B EH and uses gold grid wire for improved bias stability. BTB offers the two valves as a factory-matched pair. The publicly visible information does not state the exact factory test point or guaranteed matching tolerance.

Suitable applications

• Stereo single-ended amplifiers using one 300B per channel
• Mono or stereo output stages using two standard-operated 300B valves
• Push-pull 300B circuits with a compatible output transformer and operating point
• Valve replacement in amplifiers using UX4 sockets and 5 V filament supplies
• New builds with correctly rated filament supplies, bias circuits and plate loads

Factory matching and product configuration

Package contents

Two Electro-Harmonix 300B Gold valves

Selection type

Factory-matched pair

Matching test point

Not stated in the publicly visible product information

Matching tolerance

Not stated in the publicly visible product information

Gold version

Gold grid wire for improved bias stability according to the manufacturer

Production type

Current production, not historical NOS stock

Country of origin

Russia according to the current BTB and manufacturer information

Technical data

Valve type

Directly heated audio power triode

Type designation

300B Gold

Base

Four-pin UX4

Nominal filament voltage

5.0 V per valve

Permitted filament-voltage range

4.5 to 5.5 V according to the current data sheet

Filament current

1.1 to 1.4 A per valve

Data-sheet test point

303 V plate voltage and -58 V grid bias

Plate current at the test point

50 to 85 mA

Transconductance at the test point

4.5 mA/V minimum

Amplification factor at the test point

3.0 minimum

Output-power test

At least 5.5 W into a 2.4 kΩ plate load with 41 V RMS grid drive under the stated conditions

Distortion in the output-power test

10% maximum under the stated data-sheet conditions

Maximum plate voltage

450 V

Maximum cathode current

100 mA

Maximum plate dissipation

40 W per valve

Maximum grid-leak resistance with fixed bias

0.51 MΩ

Maximum grid-leak resistance with cathode bias

1.0 MΩ

Maximum envelope temperature

473 K, approximately 200 °C

Dimensions

Approx. Ø61.5 mm and 152 ±3 mm overall height

Pinout and filament supply

Pins 1 and 4

Filament and cathode connections

Pin 2

Plate

Pin 3

Control grid

Directly heated construction

The filament also serves as the cathode, so filament referencing and bias interact

AC filament supply

Requires a suitable winding centre tap or correctly adjusted hum-balance control

DC filament supply

Polarity, grounding, start-up behaviour and filament voltage must suit the amplifier circuit

Comparison with related valves

Electro-Harmonix 300B EH

Regular version in the same basic family; the Gold version adds the manufacturer's specified gold grid wire

2A3

Also uses a four-pin base but requires a different filament supply and different operating conditions; not an unchecked direct substitute

300B-XLS and other uprated variants

These may use higher or different limits. An amplifier exploiting their additional capacity must not automatically be fitted with a standard 300B

Selection and application notes

Factory matching supports closely corresponding values, but it does not replace measurement of the actual quiescent current. Check each valve separately where individual bias adjustment is provided; in cathode-biased circuits, verify cathode voltage and plate dissipation.

The 450 V, 100 mA and 40 W figures are limits rather than universal recommended operating values. A safe operating point depends on plate voltage, quiescent current, load impedance, filament supply and cooling.

A directly heated 300B is sensitive to asymmetric filament wiring and unsuitable grounding. Errors can introduce hum or change the effective grid bias.

300B output stages use hazardous plate voltages and the valves become very hot. Disconnect the mains supply, discharge the equipment completely and allow the valves to cool before replacement.

Questions about selection and use

Is the Electro-Harmonix 300B Gold factory-matched pair suitable for a stereo SET amplifier?

Yes, the Electro-Harmonix 300B Gold factory-matched pair is suitable for compatible stereo SET amplifiers using one 300B per channel. The UX4 base, 5 V filament supply, plate voltage, quiescent current, output transformer and mechanical clearance must suit the circuit.

Can the Electro-Harmonix 300B Gold pair replace two existing standard 300B valves?

Yes, the Electro-Harmonix 300B Gold pair can replace two standard 300B valves in a compatible amplifier when the filament supply, pinout, operating point and limits match. The 2A3, 300B-XLS and other differently rated types are not unchecked direct substitutes.

Should the bias and filament voltage be checked after installing the 300B Gold pair?

Yes, the quiescent current or bias and the 5 V filament supply must be checked after replacing the valves. Factory matching does not replace individual current measurement or verification of plate dissipation, filament referencing and hum balance.