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Tube Substitutions for:
KT88
Beam Power Tube
TypeSubstitutesBase Diagram
KT88
Web ReferencesKT88 (GEC) @ Franks Electron Tubes
KT88 (GEC) @ Franks Electron Tubes
KT88 (M-O Valve) @ Franks Electron Tubes
KT88 (Svetlana) @ Franks Electron Tubes
KT88 @ RadioMuseum.org
GEC Type KT88
BEAM TETRODE



MECHANICAL DATA

Bulb ST-16
Base Metal Shell Wafer Octal
Basing 7S


ELECTRICAL DATA


HEATER CHARACTERISTICS
Heater Voltage 6.3 Volts
Heater Current 1.6 Amps

DIRECT INTERELECTRODE CAPACITANCES
Triode Connection
Grid No.1 to Plate, Grid No. 2 7.9 ��f
Grid No. 1 to all but Plate and Grid No. 2 9.3 ��f
Plate and Grid No. 2 to all but Grid No. 1 17.0 ��f
Tetrode Connection
Grid No.1 to Plate 1.2 ��f
Input 16.0 ��f
Output 12.0 ��f

CHARACTERISTICS
Tetrode Connected
Plate Voltage 250 Volts
Grid No. 2 Voltage 250 Volts
Grid No. 1 Voltage (approx.) -15 Volts
Plate Current 140 Ma
Grid No. 2 Current (approx.) 3 Ma
Transconductance 11500 �mhos
Plate Resistance 12000 Ohms
Triode Connected
Plate and Grid No. 2 Voltage 250 Volts
Plate and Grid No. 2 Current 143 Ma
Grid No. 1 Voltage (approx.) -15 Volts
Transconductance 12000 �mhos

TYPICAL OPERATION
AB1 Push-Pull, Cathode Bias, Tetrode Connection
Plate Supply Voltage 560 Volts
Plate Voltage 521 Volts
Grid No. 2 Voltage 300 Volts
Plate Current per tube (Zero Signal) 64 Ma
Plate Current per tube (Max Signal) 73 Ma
Grid No. 2 Current per tube (Zero Signal) 1.7 Ma
Grid No. 2 Current per tube (Max Signal) 9.0 Ma
Load Resistance (Plate to Plate) 9000 Ohms
Cathode Bias Resistor1 460 Ohms
Grid No. 1 Voltage -30 Volts
Power Output 50 Watts
Total Harmonic Distortion 3 Percent
Intermodulation Distortion2 11 Percent
Anode Dissipation (Zero Signal) 33 Watts
Anode Dissipation (Max Signal) 12 Watts
Grid No. 2 Dissipation (Zero Signal) 0.5 Watts
Grid No. 2 Dissipation (Max Signal) 2.7 Watts
AB1 Push-Pull, Fixed Bias, Tetrode Connection
Plate Supply Voltage 560 Volts
Plate Voltage 552 Volts
Grid No. 2 Voltage 300 Volts
Plate Current per tube (Zero Signal) 60 Ma
Plate Current per tube (Max Signal) 145 Ma
Grid No. 2 Current per tube (Zero Signal) 1.7 Ma
Grid No. 2 Current per tube (Max Signal) 15.0 Ma
Load Resistance (Plate to Plate) 4500 Ohms
Grid No. 1 Voltage1 -34 Volts
Power Output 100 Watts
Total Harmonic Distortion 2.5 Percent
Intermodulation Distortion2 10 Percent
Anode Dissipation (Zero Signal) 33 Watts
Anode Dissipation (Max Signal) 28 Watts
Grid No. 2 Dissipation (Zero Signal) 0.5 Watts
Grid No. 2 Dissipation (Max Signal) 4.5 Watts
AB1 Push-Pull, Cathode Bias, Ultra-Linear Connection (40% tap)
Plate and Grid No. 2 Supply Voltage 500 375 Volts
Plate and Grid No. 2 Voltage 436 238 Volts
Plate and Grid No. 2 Current per tube (Zero Signal) 87 87 Ma
Plate and Grid No. 2 Current per tube (Max Signal) 99 96 Ma
Load Resistance (Plate to Plate) 6000 5000 Ohms
Cathode Resistor1 600 400 Ohms
Grid No. 1 Voltage -52 -35 Volts
Power Output 50 30 Watts
Total Harmonic Distortion 1.5 1.0 Percent
Intermodulation Distortion2 4 3 Percent
Anode and Grid No. 2 Dissipation (Zero Signal) 38 28.5 Watts
Anode and Grid No. 2 Dissipation (Max Signal) 17 16 Watts
Output Impedance 4800 4500 Ohms
AB1 Push-Pull, Fixed Bias, Ultra-Linear Connection (40% tap)
Plate and Grid No. 2 Supply Voltage 560 460 Volts
Plate and Grid No. 2 Voltage 553 453 Volts
Plate and Grid No. 2 Current per tube (Zero Signal) 50 50 Ma
Plate and Grid No. 2 Current per tube (Max Signal) 157 140 Ma
Load Resistance (Plate to Plate) 4500 4000 Ohms
Grid No. 1 Voltage3 -75 -59 Volts
Power Output 100 70 Watts
Total Harmonic Distortion 2 2 Percent
Intermodulation Distortion2 11 10 Percent
Anode and Grid No. 2 Dissipation (Zero Signal) 27.5 22.5 Watts
Anode and Grid No. 2 Dissipation (Max Signal) 33 27 Watts
Output Impedance 7000 6500 Ohms
AB1 Push-Pull, Cathode Bias, Triode Connection
Plate and Grid No. 2 Supply Voltage 400 485 Volts
Plate and Grid No. 2 Voltage 349 422 Volts
Plate and Grid No. 2 Current per tube (Zero Signal) 76 94 Ma
Plate and Grid No. 2 Current per tube (Max Signal) 80 101 Ma
Load Resistance (Plate to Plate) 4000 4000 Ohms
Grid No. 1 Voltage -40 -50 Volts
Power Output 17 31 Watts
Total Harmonic Distortion 1.5 1.5 Percent
Intermodulation Distortion2 5.6 5.6 Percent
Anode and Grid No. 2 Dissipation (Zero Signal) 26.5 40 Watts
Anode and Grid No. 2 Dissipation (Max Signal) 19 27 Watts
Cathode Resistor 525 525 Ohms
Output Impedance 2000 1900 Ohms

NOTES:

1 It is essential to use two seperate cathode bias resistors.
2 Intermodulation distortion; measured using two input signals at 50 and 6000Hz (ratio of amplitudes 4:1)
3 It is essential to provide two separately adjustable bias voltage sources, having a voltage adjustment range of �25%.

INSTALLATION

The tube may be mounted either vertically or horizontally.
When tubes are mounted vertically it is recommended that the centres of the tube sockets are not less than 4in. apart and that pins 4 and 8 of each tube are in line.
When tubes are mounted horizontally it is recommended that the centres of the tube sockets are not less than 4in. apart and that pins 4 and 8 of each tube are in teh same vertical line. One tube should not be mounted directly above another. Free air circulation around the tube is desireable.



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