5751 JJ tube low Gain Röhre V1+low mic+lownoise Röhren Set

JJ 5751 – low-noise and low-microphony V1 set of two

The JJ 5751 is an indirectly heated dual triode with two separate gain systems, a B9A Noval base and a typical amplification factor of 70. It is suitable for compatible preamplifier stages requiring less gain and greater signal headroom than an ECC83 or 12AX7.

This BTB set contains two valves selected for low microphony and low noise in sensitive V1 positions. The optional matched / balanced grade additionally groups the four triode systems in the two valves for closely corresponding electrical measurements.

Suitable applications

• V1 input stages in compatible guitar and bass amplifiers
• Preamplifiers where a 12AX7 circuit should operate with less voltage gain
• Hi-fi, line-level and studio preamplifiers with a suitable operating point
• Phase-inverter and differential stages when the matched / balanced option is selected
• Stereo circuits using one 5751 per channel
• Valve replacement where the heater supply can provide the higher current compared with a typical ECC83

BTB selection and options

Package contents

Two JJ 5751 valves

Standard selection

Checked for low microphony and low noise in V1 applications

Matched / balanced option

Additional electrical selection of all four triode systems for closely corresponding parameters

Matched

Refers to closely corresponding measurements between the two valves

Balanced

Refers to closely corresponding systems within each dual triode

Country of origin

Slovakia according to the current BTB product page

Technical data

Valve type

Indirectly heated low-gain audio dual triode

Type designation

5751

Base

Nine-pin B9A Noval

Heater voltage

6.3 V in parallel or 12.6 V in series

Heater current

Approx. 350 mA at 6.3 V or 175 mA at 12.6 V

Typical operating point per system

100 V plate voltage and -1 V grid bias

Plate current at the typical point

Approx. 0.8 mA

Amplification factor

Approximately 70

Transconductance

Approx. 1.2 mA/V

Plate resistance

Approx. 58 kΩ

Maximum plate voltage

300 V

Maximum negative grid voltage

-50 V

Maximum plate dissipation

1 W per triode system

Maximum heater-to-cathode voltage

180 V according to the current JJ data sheet

Dimensions

Maximum diameter approx. 22 mm and overall height approx. 56.3 mm

Pinout and heater wiring

Pin 1

Plate of triode system 1

Pin 2

Control grid of triode system 1

Pin 3

Cathode of triode system 1

Pins 4 and 5

Heater connections

Pin 6

Plate of triode system 2

Pin 7

Control grid of triode system 2

Pin 8

Cathode of triode system 2

Pin 9

Centre connection of the split heater

6.3 V heater connection

Join pins 4 and 5 and apply the supply between this connection and pin 9

12.6 V heater connection

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

Comparison with 12AX7 and 12AY7

5751

Typical amplification factor of 70 and heater current of approximately 350 mA at 6.3 V

ECC83 or 12AX7

Typical amplification factor around 100 and normally 300 mA heater current at 6.3 V; not electrically identical in every circuit

12AY7 or 6072A

Lower amplification factor and a different operating point, providing a greater gain reduction but not an identical replacement for the 5751

Selection and application notes

The 5751 shares the base and heater-voltage arrangement of the ECC83 or 12AX7 but typically draws approximately 50 mA more at 6.3 V. Check the heater-winding reserve, especially when replacing several valves together.

The actual gain reduction depends on the plate resistor, cathode circuit, feedback and following load. An amplification factor of 70 does not therefore produce exactly 70% of the previous stage gain in every circuit.

For a simple cascaded V1 stage, low acoustic noise is often more important than perfect internal section balance. The matched / balanced option can provide additional value in stereo, differential and phase-inverter circuits.

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

Questions about selection and use

Is the JJ 5751 V1 set suitable for compatible 12AX7 stages requiring less gain?

Yes, the JJ 5751 V1 set is suitable for compatible 12AX7 or ECC83 stages where a lower amplification factor and greater signal headroom are required. The heater supply must be able to provide approximately 350 mA per valve at 6.3 V.

Can the JJ 5751 replace an ECC83 or 12AX7?

Yes, the JJ 5751 can be used in many compatible ECC83 or 12AX7 circuits because the base and heater-voltage connections match. The operating point, heater-current reserve, required gain and function of the particular valve position must still be checked.

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

Yes, the matched / balanced option is useful when both valves and all four triode systems should operate as similarly as possible, for example in stereo, differential or phase-inverter stages. In a simple V1 cascade, the included low-microphony and low-noise selection is often more important.