12AX7EH ECC83 Electro Harmonix V1+low mic+lownoise Röhren Set
Two V1 valves selected for low noise, low hum and low microphony use
For audio, hi-fi, studio and guitar preamps requiring high gain
Optional matched/balanced grading aligns all four triode sections
Electro-Harmonix 12AX7EH – low-noise and low-microphony V1 set of two
This set contains two current-production Electro-Harmonix 12AX7EH valves. Each valve is an indirectly heated high-gain dual triode with two separate systems, a nine-pin B9A Noval base and a heater configurable for 6.3 or 12.6 V.
BTB selects both valves for sensitive V1 and input positions with attention to low noise, low hum and low microphony. An optional matched / balanced grade additionally groups the 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, line-level and studio preamplifiers using 12AX7 or ECC83 valves
- Phono and microphone preamplifiers whose circuits specify this valve type
- Stereo voltage-gain stages using one dual triode per channel
- SRPP, differential and phase-inverter stages with matched / balanced grading
- Replacement in equipment requiring 12AX7, ECC83 or 7025 valves
BTB selection and options
- Package contents
- Two Electro-Harmonix 12AX7EH valves
- Standard selection
- Checked for low microphony, low noise and low hum 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 measurements
- Production type
- Current production, not historical NOS stock
- Country of origin
- Russia according to the current BTB product information
Technical data
- Valve type
- Indirectly heated high-gain dual triode
- Type designations
- 12AX7EH, 12AX7 and ECC83; technically related to many 7025 applications
- Base
- Nine-pin B9A Noval
- Parallel heater voltage
- 6.3 V nominal
- Heater current at 6.3 V
- 320 to 365 mA per valve
- Series heater voltage
- 12.6 V nominal
- 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
- Transconductance at the test point
- 1.4 mA/V minimum
- Amplification factor
- 83 minimum in the current production sheet; the typical basic-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
- Dimensions
- Maximum overall height approximately 56.5 mm and envelope diameter approximately 22.5 mm
Pinout and heater wiring
- Pins 1 to 3
- Plate, control grid and cathode of triode system 2
- Pins 6 to 8
- Plate, control grid and cathode of triode system 1
- Pins 4, 5 and 9
- Connections of the split heater
- 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 related dual triodes
- 12AX7 and ECC83
- American and European designations of the same basic high-gain dual-triode family
- 7025
- Historically a particularly low-noise 12AX7 version; the equipment specification remains decisive
- 5751
- Pin-compatible dual triode with a lower amplification factor and different heater demand
- 12AY7 or 6072A
- Substantially lower gain and a different operating point; not an identical direct substitute
Selection and application notes
V1 selection focuses on acoustic quietness. In a simple cascaded input stage, this is often more important than especially close section balance. The additional matched / balanced grade can provide technical value in stereo, SRPP, differential and phase-inverter stages.
Heater current can reach 365 mA, slightly above the classic 300 mA figure of some ECC83 versions. Check the heater-transformer reserve when replacing several valves together.
High voltage gain makes a stage more sensitive to grounding errors, long grid wiring and microphony. Short signal paths, suitable grid stoppers and effective supply decoupling support stable operation.
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 Electro-Harmonix 12AX7EH V1 set suitable for sensitive audio and guitar input stages?
Yes, the Electro-Harmonix 12AX7EH V1 set is suitable for compatible audio, hi-fi, studio and guitar input stages specifying a 12AX7 or ECC83. The heater supply, operating point and function of the particular valve position must suit the circuit.
Can the Electro-Harmonix set replace two existing 12AX7, ECC83 or 7025 valves?
Yes, the Electro-Harmonix set can replace two compatible 12AX7, ECC83 or 7025 valves when the base, heater wiring, operating point and limits match. A 5751 or 12AY7 has different gain and operating characteristics.
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 stage, the included low-noise and low-microphony selection is often more important.
Note: All brand names mentioned, such as Marshall, Fender, etc., are registered trademarks of their respective owners and are used here for descriptive and compatibility purposes only.
BTB Elektronik Vertriebs GmbH Kepler Strasse 6
DE-90766 Fürth
Email: info@btb-elektronik.de
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Fact sheet on EU Directive 2011/65/EURestriction of the use of hazardous substances in electrical and electronic equipment (PDF, not accessible, 2 MB)
Source: IHK Mittelfranken
Tariff Number: 85408100
Country of Origin: RU