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30 November 2021 

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KT88 tube data (electron valve/beam power tetrode/output Beam pentode)

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Photo of a Billington Gold KT88 Photo of a GEC Style KT88 manufactured in China Photo of a Kesla KT88
Photo of a JJ KT88 Photo of four used GEC KT88s

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General Information

The KT88 can be either a beam power tetrode or output beam pentode depending on the circuit.

It has a high anode dissipation rating. Enhanced sonic performance, including: increased peak cathode emission, stable operation. Can be used as direct replacement for KT9o, KT99 and 6550.


Heater Voltage                                                     6.3          V             Vh

Heater Current                                                     1.8          A             Ih

Maximum Anode Voltage                       800       V          Va(max)

Maximum Screen grid voltage                600       V          Vg2(max)

Maximum Control Grid Voltage              -300      V          Vg1(max)

Maximum Voltage between Grids 1&2    400       V          Vg1-g2(max)

Maximum Anode Dissipation                 42         W         Pa(max)

Maximum Screen Dissipation                 8          W         Pg2(max)

Maximum Cathode Current                     230       mA       Ik(max)

Maximum Heater to Cathode Voltage     250       V          Vh-k(max)

                        (DC Heater negative)

Maximum Heater to Cathode Voltage     250       V          Vh-k(max)

                        (DC Heater positive


Pentode Connection                                             Triode Connection

Va                    250V                                                    Va,g2               450V

Vg2                  250V                                                    Vg1                  -46V

Ia                     140mAg                                              gm                   13mA/V

Ra                   12kΩ                                                   ra                     6.5kΩ

µg1-g2             8                                                          µ                      8


Push-Pull, Ultra Linear, Cathode Bias (Data per pair)

Va,g2                           335V                 425V

Ia+g2 (0)                       80mA                174mA

Ia+g2 (Max sig)             85mA                200mA

Pa+g2 (0)                      27w                  80W

Pa+g2 (Max sig)            12W                  36W

Rk (per valve)                400Ω                525Ω

Vg (approx)                  -32V                 -50V

P out                            30W                  50W*

RL (a-a)             5K Ω                 6kΩ

D                                  1%                   2*%

* These figures refer to an average pair. With a matched pair the distortion will be reduced and with an unmatched pair it may rise to 4%.

Push-Pull, Ultra Linear, Fixed Bias (Data per pair)

Va,g2                           450V                 550V

Ia+g2 (0)                       100mA              100mA

Ia+g2 (Max sig)             240mA              300mA

Pa+g2 (Max sig)            40W                  66W

*Vg                               -65V                 -80V

P out                            65W                  100W*

RL (a-a)             4kΩ                  4.5kΩ

Z out                            6.5kΩ               6.5kΩ

†D                                3 to 6%             3 to 6%

* A bias voltage range of at least 25% is recommended.

† The distortion will vary according to the degree of matching


Grid/Earth                                             16         c in

Anode/Earth                                          12         c out

Anode/Grid                                           1.2        cg-a

Without external shielding


Maximum overall length                     125      mm

Maximum seated height                     110      mm

Maximum diameter                            52        mm

Net weight                                           g

BASE – Metal – Octal

Chart showing KT88 data

Click here for information about replacing a KT88 Beam Tetrode with a 12E1 Beam Terode

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