Western Electric KT-88 Brochure

GOLD LION
KT88

Made in England

Draft of new spec sheet 4/30/2002

BEAM TETRODE

6-3V INDIRECTLY HEATED

The KT88 has an absolute maximum anode dissipation rating of 42W and is designed
for use in the output stage of an a.f. amplifier. Two valves in Class AB1 give a continuous output of up to 100W.
The KT88 is also suitable for use as a series valve in a stabilized power supply.

The KT88 is a commercial version of the CV5220 and is similar to the 6550.

BASE CONNECTIONS AND VALVE DIMENSIONS

HEATER

Vh 6.3 V
Ih 1.6 (approx) A

Base: Metal shell wafer octal

Bulb: Tubular

Max. Overall length: 125 mm

Max. Seated length: 110 mm

Max.Diameter: 52 mm

MAXIMUM RATINGS

Absolute Design Maximum Units
Va 800 800 V

g2 600 600 V

V
V

a, g 2 600 600 V

Vg 1 200 200 V
Pa 42 35 W

g2 8 6 W

P
P

a+g2 46 40 W

I k 230 230 ma
Vh-k 250 200 V
Tbulb 250 250 degrees C
Rg1-k (cathode bias)
Pa|g2 < 135W 470 k ohm
Pa|g2 > 35W 270 k ohm

Rg1-k (fixed bias)
Pa|g2 < 135W 220 k ohm
Pa|g2 > 35W 100 k ohm

CAPACITANCES (Measured on a cold unscreened valve)

Triode Connection

Cg1-a.g.2: 7.9pF Cg1-all less a.g2: 9.3pF Ca.g2 -all less g1 : 17pF

Tetrode Connection

Cg1-a: 1.2pF Cal -all less a: 16pF Ca -all less g1 : 12pF

CHARACTERISTICS

Tetrode Connected

a 250 V

V
Vg2 250 V
I

a 140 mA

Ig2 3 (approx) mA
Vg1 15 (approx) V
gm 11.5 mA/V
ra 12 ohms

g1-g2 8 --

µ

Triode Connected
Va,g2 250 V
I

a+ g2 143 mA

-Vg1 15 approx V

m 12 mA/V

g
ra 670 ohms
µ 8 --

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TYPICAL OPERATION

Push-Pull. Class AB1.
Cathode Bias. Tetrode Connection

Va(b) 560 V

Va(o) 521 V

Vg2 300 V
Ia(o) 2 x 64 mA
Ia(max. sig) 2 x 73 mA
Ig2(o) 2 x 1.7 mA
Ig2(max. sig) 2 x 9 mA
RL(a-a) 9 kohm

k* 2 x 460 ohm

R

-V

g1 30 (approx) V

Pout 50 W
Dtot 3 %
I.M. 11 %
Pa(o) 2 x 33 W
Pa(max. sig) 2 x 12 W
Pg2(o) 2 x 0.5 W
Pg2(max. sig) 2 x 2.7 W
Vin(g1-g1)(pk) 60 V

*It is essential to use two separate cathode bias resistors.
**Intermodulation distortion: measured using two input
signals at 50 and 6000 hz (ratio of amplitudes 4:1)

Push-Pull. Class AB1.
Fixed Bias. Tetrode Connection

Va(b) 560 V
Va(o) 552 V
Vg2 300 V
Ia(o) 2 x 60 mA
Ia(max. sig) 2 x 145 mA
Ig2(o) 2 x 1.7 mA

g2(max. sig) 2 x 15 mA

I
R

L(a-a) 4.5 kohm

-Vg1 34 (approx) V
Pout 100 W
Dtot 2.5 %
I.M. 10 %
Pa(o) 2 x 33 W
Pa(max. sig) 2 x 28 W
Pg2(o) 2 x 0.5 W
Pg2(max. sig) 2 x 4.5 W
Vin(g1-g1)(pk) 67 V

*It is essential to provide two separately adjustable bias voltage
sources, having a voltage adjustment range of 25%.
**Intermodulation distortion: measured using two input signals
at 50 and 6000 hz (ratio of amplitudes 4:1).

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