12AX7 Tung-Sol tube set V1+low mic+lownoise Röhren Set

Tung-Sol 12AX7 / ECC83 – low-noise and low-microphony V1 set of two

This set contains two current-production Tung-Sol 12AX7/ECC83 valves. Each valve is an indirectly heated high-gain dual triode with two separate systems, a nine-pin B9A Noval base and a configurable 6.3 or 12.6 V heater.

BTB selects both valves for sensitive V1 positions with attention to low noise, low hum and low microphony. An optional matched / balanced grade additionally selects the two valves so that all four triode systems have closely corresponding electrical values.

Suitable applications

• V1 input stages in compatible guitar and bass amplifiers
• Hi-fi and studio preamplifiers using 12AX7 or ECC83 valves
• Phono and microphone preamplifiers whose circuits explicitly specify this type
• Stereo line-level and voltage-gain stages
• SRPP, differential and phase-inverter stages with the matched / balanced option
• Replacement in equipment requiring 12AX7, ECC83 or 7025 valves

BTB selection and options

Package contents

Two Tung-Sol 12AX7/ECC83 valves

Standard selection

Checked for low microphony, low hum and low noise in V1 applications

Matched option

The two valves are grouped for closely corresponding electrical measurements

Balanced option

The two triode systems within each valve are selected for closely corresponding values

Manufacturer classification

High-gain dual triode equivalent to 12AX7, ECC83 and 7025 applications

Factory matching

Platinum Matching is not offered for the individual type; the shop option refers to BTB selection

Production type

Current production

Country of origin

Russia according to current BTB and manufacturer information

Technical data

Valve type

Indirectly heated high-gain audio dual triode

Type designations

12AX7, ECC83 and 7025

Base

Nine-pin B9A Noval

Parallel heater voltage

6.3 V nominal; permitted data-sheet range 6.0 to 6.6 V

Heater current at 6.3 V

320 to 365 mA per valve

Series heater voltage

12.6 V nominal; permitted data-sheet range 12.0 to 13.2 V

Heater current at 12.6 V

160 to 183 mA per valve

Data-sheet test point per triode

250 V plate voltage and -2.0 V control-grid voltage

Plate current at the test point

0.75 to 2.1 mA

Permitted production-section difference

Up to ±40% plate-current difference between the two systems at the test point

Transconductance at the test point

1.4 mA/V minimum

Amplification factor

83 minimum in the current production sheet; the typical 12AX7/ECC83 type value is approximately 100

Maximum plate voltage

330 V per triode system

Maximum plate dissipation

1.2 W per triode system

Maximum cathode current

9 mA per triode system

Maximum heater-to-cathode voltage

±200 V

Maximum grid-circuit resistance with fixed bias

1.0 MΩ per system

Maximum grid-circuit resistance with cathode bias

2.2 MΩ per system

Dimensions

Maximum overall height approximately 56.5 mm and envelope diameter approximately 22.5 mm

Pinout and heater wiring

Pin 1

Plate of triode system 2

Pin 2

Control grid of triode system 2

Pin 3

Cathode of triode system 2

Pins 4, 5 and 9

Connections of the split heater

Pin 6

Plate of triode system 1

Pin 7

Control grid of triode system 1

Pin 8

Cathode of triode system 1

6.3 V heater connection

Join pins 4 and 5 and apply 6.3 V between this connection and pin 9

12.6 V heater connection

Apply 12.6 V between pins 4 and 5; pin 9 is not used for the heater supply

Comparison with ECC83, 7025, 5751 and 12AY7

12AX7 and ECC83

American and European designations of the same basic high-gain dual-triode family

7025

Historically a low-noise 12AX7 version; Tung-Sol identifies the current type as 7025 equivalent

5751

Pin-compatible dual triode with a lower amplification factor and different heater demand; useful for moderate gain reduction

12AY7 or 6072A

Uses substantially lower gain and a different operating point; useful for greater gain reduction but not an identical substitute

Sound positioning

BTB subjectively describes the version as neutral to slightly warm, while Tung-Sol describes a warm, dynamic and spacious presentation. The audible result also depends on the operating point, plate load, cathode circuit, coupling capacitors, feedback and complete audio system.

Selection and application notes

BTB's V1 selection focuses on acoustic quietness. In a simple cascaded input stage, this is often more important than especially close section balance. The optional matched / balanced grade provides additional technical value in stereo, differential, SRPP and phase-inverter stages.

Heater current can reach 365 mA, slightly above the classic 300 mA figure of many ECC83 versions. Check the heater-transformer reserve when replacing several valves together.

High voltage gain makes an unsuitable layout more susceptible to hum, microphony and radio-frequency oscillation. Short grid wiring, suitable grid stoppers, effective grounding and supply decoupling are important.

Hazardous plate voltages and stored charge may remain inside the equipment. Disconnect the mains supply, discharge the circuit and allow the valves to cool before replacement.

Questions about selection and use

Is the Tung-Sol 12AX7 V1 set suitable for sensitive audio and guitar input stages?

Yes, the Tung-Sol 12AX7 V1 set is suitable for compatible audio, hi-fi, studio and guitar input stages specifying a 12AX7, ECC83 or 7025. The heater supply, operating point and function of the particular valve position must suit the circuit.

Can the Tung-Sol set replace two existing ECC83, 12AX7 or 7025 valves?

Yes, the Tung-Sol set can replace two compatible ECC83, 12AX7 or 7025 valves because the base, system construction and heater wiring belong to the same basic family. A 5751 or 12AY7 has different gain and operating data and is not an identical substitute.

Is the matched / balanced option useful for stereo, SRPP or phase-inverter stages?

Yes, the matched / balanced option is useful in such circuits because it supports closely corresponding values between the two valves and across all four triode systems. In a simple V1 input stage, the included low-noise and low-microphony selection is often more important.