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KT88

Output beam tetrode

Field	Value
image	Kt88.jpg
image_size	100px
caption	KT88 labeled G.E.C. made by GEC/MOV in the U.K.
classification	Beam-power tetrode
service	Class-A amplifier, (single-ended)

height_in
diameter_in
weight_lbs
cathode_type	Indirectly-heated
heater_voltage	6.3
heater_current	1.6A
max_dissipation	42W
max_voltage	800
pinout	Octal base, (IO)

class_a_anode_voltage	250V
class_a_anode_current	140mA
class_a_screen_voltage	250V
class_a_bias_voltage	-15V
class_a_anode_resistance	12 kilohms
class_ab_power_output	100W
class_ab_anode_voltage	600V
class_ab_anode_current	100mA
class_ab_screen_voltage	350V
class_ab_bias_voltage	-45 (class AB2)
reference	Super Radiotron Tube Manual, Amalgamated Wireless Valve Co. Australia, June 1962

The KT88 is a beam tetrode/kinkless tetrode (hence "KT") vacuum tube for audio amplification.

class-AB amplifier, (push-pull)

Pin 1, Not used

Pin 2, Heater

Pin-3, Anode/plate

Pin-4, Screen grid, g2

Pin-5, Control grid, g1

Pin-6, Not used

Pin-7, Heater

Pin-8, Cathode-beam plates

Radio Tube Data, Eighth Ed. Ilife Books Ltd., London, 1966

Features

The KT88 fits a standard eight-pin octal socket and has similar pinout and applications as the 6L6 and EL34. Specifically designed for audio amplification, the KT88 has higher plate power and voltage ratings than the American 6550. It is one of the largest tubes in its class and can handle significantly higher plate voltages than similar tubes, up to 800 volts. A KT88 push-pull pair in class AB1 fixed bias is capable of 100 watts of output with 2.5% total harmonic distortion or up to about 50W at low distortion in hi-fi applications. The transmitting tubes TT21 and TT22 have almost identical transfer characteristics to KT88 but a different pinout, and by virtue of their anode being connected to the top cap have a higher plate voltage rating (1.25 kilovolt) and a higher power output capability of 200 watts in class AB1 push–pull.

The screen grid is sometimes tied to the anode so that it becomes effectively a triode with a lower maximum power output.

History

The KT88 was introduced by GEC in 1956 as a larger variant of the KT66. It was manufactured in the U.K. by the MOV (Marconi-Osram Valve) subsidiary of G.E.C, also labelled as IEC/Mullard, and, in the U.S., Genalex Gold Lion.

As of 2022, KT88 valves are produced by New Sensor Corporation (Genalex Gold Lion and Electro-Harmonix brands) in Saratov, Russia, JJ Electronic in Čadca, Slovakia and Hengyang Electronics (Psvane brand) at former Guiguang factory in Foshan, China.

NOS examples in good condition are extremely rare. Due to its availability and characteristics, the KT88 is popular in hi-fi production amplifiers.

Historically, it has been far more popular with high fidelity stereo manufacturers than guitar amplifier builders, given its characteristics of high-power and low-distortion. Due to these characteristics, it is regularly used to replace 6550 tubes by end users seeking a guitar amplifier tone with less distortion. Some of the amplifiers which shipped with the KT88 power tube include the Hiwatt, Marshall Major, and some Ampeg models.

Characteristics

Kt88pent.gif|Anode characteristics

References

https://frank.pocnet.net/sheets/086/k/KT88.pdf ''KT88 Datasheet''
"6550/KT88 Power Kings Part II". Vacuum Tube Valley Quarterly, 2003, Issue 19.
"New Sensor Corporation".
"JJ Electronic s.r.o.".
"Changsha Hengyang Electronics Co., Ltd.".
Fliegler, Ritchie. (1993). "Amps!: the other half of rock 'n' roll". Hal Leonard.
Aspen Pittman. (2003). "The Tube Amp Book". Backbeat.

Info: Wikipedia Source

This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page.

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