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24 March 2018 

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ECC81 Mullard tube/12AT7 RCA valve/ 12AT7 tube data

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Photo of Brimar ECC81/12AT7 Electron Tube / Double Triode Photo of Billington Gold ECC81/12AT7 Electron Tube / Double Triode Photo of Sylv 3 Mica Sqgetter ECC81/12AT7 Electron Tube / Double Triode

General Information

An indirectly heated, oxide coated, twin cathode double triode. Each triode is a separate unit, the heaters being the only common connection. As a result it is possible to use each unit for different functions or both in cascade. The feature of a heater tap allows for both A.C. & D.C. supply.

CATHODE Indirectly heated by A.C. or D.C.; series or parallel supply


                                  Series - pins 9-(4+5)        parallel - pins 4+5


Heater Voltage                            12.6                              6.3                    V

Heater current                            150                               300                   mA

In case of series supply a current limiting device must be inserted in the heater circuit for limiting the current when switching on.

Max D.C. Heater –Cathode Potential                      250                               V

MAXIMUM RATINGS (each triode unit)

Maximum anode voltage                           Va0       550                   V

                                                                        Va         300                   V

Maximum anode dissipation                      Wa       2.5                    W

Maximum Cathode Current                       Ik          15                     mA

Maximum  Grid Voltag                             -Vg        50                     V

Maximum Grid Resistance                         Rg         1                      MΩ

                 (automatic bias)

Maximum Cathode to heater voltage           Vkf        90                     V


Anode Voltage                Va                     100       170       200       250       V

Grid Voltage                   Vg                     -1.0       -1.0       -1.0       -2.0       V

Anode Current               Ia                      3.0        8.5        11.5      10         mA

Transconductance           S                       3.75      5.9        6.7        5.5        mA/V

Amplification Factor         µ                      62         66         70         60

Internal resistance            Ri                     16.5      11         10.5      11         Kω


Maximum overall length                                        55.6                  mm

Maximum seated height                                        49.2                  mm

Maximum diameter                                              22.2                  mm

Base                                                          Noval B9A


Pin1 Anode   )
Pin2      Grid      )---- Second Triode Unit
Pin3      Cathode )

Pin4      Heater
Pin5      Heater

Pin6      Anode   )
Pin7      Grid      )----- First Triode Unit
Pin8      Cathode )

Pin9      HeaterTap

Illustration of ECC81/12AT7 Pin9 Heater Tap

CAPACITIES (Approx) (Measured without shield)

Grounded Cathode Operation                        

First triode Unit               Second Triode Unit


Grid – Anode                             1.45                  1.45      pF

Grid – Cathode, Heater                2.5                    2.5        pF

Grid – Cathode, Heater                0.45                  0.35      pF

Heater – Cathode                        2.5                    2.5        pF


CAPACITIES (Approx)  cont.


Grid 1 – Anode 2                                                0.20      pF

Grid 2 - Anode 1                                    0.20      pF

Anode 1 – Anode2                                  0.40      pF max.

Grid 1 – Grid 2                                      0.005    pF max.


Grounded Grid Operation


First triode Unit               Second Triode Unit


Anode – Cathode                        0.15                  0.15      pF

Cathode – Grid, Heater                5                      5          pF

Anode – Grid, Heater                  1.6                    1.5        pF

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Chart showing  ECC81/12AT7 technical data
Chart showing  ECC81/12AT7 technical data

Click here to add this valve to your shopping basket

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