KT90 Beam Tetrode Data Sheet

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♦ PDF Cover Page ♦ ♦ Verso Filler Page ♦ KT 90A BEAM TETRODE For Audio Frequency Power Ampliﬁer Applications

HE KT90A is a beam power-tetrode designed for use in audio fre- Tquency power amplifiers. It is rated for 50 watts of anode+screen dissipation. With a B+ supply of 550 volts and a screen supply of 400 volts, this rating allows a power output of 110 watts per push-pull pair to be realized. With a plate supply of 750 volts and a screen supply of 600 volts, 160 watts per push-pull pair can be derived. The KT90A is an unusually robust construction that embodies a number of unique design features which account for its superior performance, both items of longevity and musicality. Due to the large, high–current-capacity (high perveance) cathode and a unique internal geometry, the tube exhibits a lower plate resistance—Rp—than its con- temporaries. This generally provides bass performance that sounds as if the low frequency roll-off point of the amplifier has been extended downwards by approximately half an octave. The tube is recommended as a direct replacement for the 6550, 6550A, 6CA7, EL34, KT77 & KT88. It can be used in circuits employing these devices by merely adjusting the bias voltage to allow the desired idle current to flow. As the majority of power amplifiers provide an ade- quate range of bias-voltage adjustment, the KT90A can serve well in a wide variety of applications. To achieve good performance in the upper registers, a very high vacuum must be created within the glass envelope. This is accom- plished by a good, initial pump-out and finished by the use of sacrificial elements within the tube that are induction heated to burn away and bind any remaining gases into harmless metallic compounds. In order for the tube to sound consistently good throughout its use- ful life, a high-quality vacuum must be maintained in spite of the high operating temperatures normally experienced. A conventional soft glass envelope presents a real problem in terms of maintaining this vacuum because at elevated temperatures it becomes somewhat “porous”, allowing the ingress of atmospheric gases. These diminish the quality of the vacuum and as running time accumulates, the electron-emitting coating on the cathode is severely damaged. The susceptibility of a hard KT 90A glass like Pyrex to high-temperature–induced porosity is very much Actual Size lower than conventional, inexpensive soft glass. A heavy Pyrex envelope encloses the KT90A. G2 G1 To further inhibit the development of porous hot spots on the glass 4 5 envelope, a unique double-layer plate structure has been developed. This construction provides a thermal diffusion effect that more evenly A 3 6 n/c heats the surrounding glass bulb resulting in a lower average-temperature that facilitates extended tube life. Good unit-to-unit consistency is achieved through careful, accurate production and assembly of the constituent parts of the tube. In partic- H 2 7 H ular, the alignment of the screen and control grids is maintained to a high level of precision. 1 8 The KT90A is a cool running, rugged device that is unmatched for n/c K & Beam former sonic quality. When next you re-tube your amplifier a decision to use the KT90A will bring a greater level of listening satisfaction. Basing Diagram

♦ Data KT90A - Page 1 ♦ 500 VACUUM TUBE LOGIC OF AMERICA, INC. 450 0V KT 90A Tetrode Screen = 300V 4774 Murietta Street #9, Chino, California, A 400 -5V 91710 USA n o 350 Ph. 714-627-5944 / 8263 Fx. 714-627-6988 d AMERICA e

C 300 -10V KT 90A CONDENSED SPECIFICATIONS u r 250 r e -15V MECHANICAL C ...... 22 pF n g1 to all less anode t 200 Mounting position...... Any Canode to all less g1 ...... 12.5 pF - -20V Envelope...... Pyrex™ 150 Basing...... Octal 8 Pin TETRODE CHARACTERISTICS M a 100 -25V Diameter...... 1.5 Inch Va ...... 300 V Seated height ...... 4.5 Inch V ...... 300 V -30V g2 50 ♦ Ia ...... 195 mA -35V

FILAMENT Ig2 ...... 3.5 mA 0 0 50 100 150 200 250 300 350 400 450 500 550 600 650 Vheater AC/DC...... 6.3 ±.6 V Vg1 ...... -15 V Anode Voltage - Volts I heater AC/DC...... 1.6 A gm ...... 16 mA/V Ω R anode...... 16 k µ ...... 9 MAXIMUM RATINGS g1 to g2 500

Vanode...... 850 V 450 0V KT 90A Triode Vg2 (screen) ...... 650 V TRIODE CHARACTERISTICS

V ...... 650 V Va & g2 ...... 250 V a & g2-triode connection 400 Data KT90A - Page 2 A V ...... -200 V I ...... 140 mA -10V ♦ g1 (control) a+g2 n Anode ...... 46 W V ...... -15 V o dissipation g1 d 350 Screen ...... 8 W g ...... 16 mA/V dissipation m e -20V R ...... 650 Ω 300 Anode + screen total ...... 50 W anode C I ...... 500 mA µ ...... 9 u k max r I ...... 230 mA r 250 -30V k e PUSH-PULL,AB1,TETRODE,FIXED BIAS n t 200 -40V CAPACITANCES E supply ...... 700 V V ...... 690 V - (Measured on a cold, unshielded tube) a 150 -50V TRIODE CONNECTION Vg2 ...... 375 V M a 100 Cg1 to anode+g2...... 8.0 pF Vg1 ...... -40 V -60V Ω C ...... 9.3 pF R load (anode to anode) ...... 3 k g1 to all less anode+g2 50 -70V Ca+g2 to all less g1 ...... 17 pF Pout...... 100 W Vg1 to g1 (pp)...... 80 V 0 TETRODE CONNECTION Iidle/tube (anode+screen)...... 40 mA 0 50 100 150 200 250 300 350 400 450 500 550 600 650

Cg1 to anode ...... 2.0 pF Imax/tube (anode+screen) ...... 150 mA Anode Voltage - Volts