Care and Feeding of Power Grid Tubes: Introduction

CARE AND FEEDING
OF POWER GRID
TUBES
PREPARED BY THE STAFF OF
CPI, EIMAC DIVISION
Communications & Power Industries
CPI, EIMAC DIVISION
301 INDUSTRIAL ROAD
SAN CARLOS, CA 94070
USA
CARE AND FEEDING OF POWER GRID TUBES
5th Edition
Copyright© 2003 by Eimac Division of CPI, Inc. All rights
reserved. Printed in the United States of America. This book,
or parts thereof may not be reproduced in any form without
permission of the publisher.
Table of Contents
SECTION I
1
INTRODUCTION
1
SECTION 2
3
WHAT IS A POWER GRID TUBE?
3
2. 1
TRIODES
3
2.2
TETRODE 8
2.3
PENTODES
2.4
Current Division 14
2.5
INDUCTIVE OUTPUT TUBE (IOT)
2.6
MULTISTAGE DEPRESSED COLLECTOR IOT
(MSDC IOT)
21
2.7
CATHODE EMITTERS
2.8
GRIDS
29
2.9
ANODES
31
2.10
VACION PUMPS 32
13
16
24
SECTION 3
ELECTRICAL DESIGN CONSIDERATIONS
35
35
v
3.1
CLASS OF OPERATION 35
3.2
TUBE PERFORMANCE COMPUTER FOR R-F
AMPLIFIERS
37
3.3
TYPICAL RF AMPLIFIER CIRCUIT DESIGNS
52
3.4
COMPONENT PARTS
3.5
LEAD LENGTHS 58
3.6
FILAMENT BY-PASSING 60
3.7
SCREEN AND SUPPRESSOR GRID BY-PASSING
AND SCREEN TUNING 62
3.8
GROUNDED-GRID CIRCUITS 63
3.9
PROTECTION
3.10
KEYING
3. 11
AMPLITUDE MODULATION
3.12
POWER SUPPLY CONSIDERATION
3.13
STABILIZING THE AMPLIFIER 76
3.14
NOISE IN TUBE AMPLIFIERS 81
57
65
70
73
75
SECTION 4
83
LINEAR AND SINGLE SIDEBAND SERVICE
4.1
WHY SINGLE SIDEBAND
4.2
RATING TUBES FOR LINEAR AMPLIFIER
SERVICE 84
vi
83
83
4.3
SELECTION OF TUBES FOR SINGLE SIDEBAND
SERVICE 92
4.4
LINEAR AMPLIFIER DESIGN
4.5
ADJUSTING AND MONITORING THE LINEAR
AMPLIFIER 105
100
SECTION 5
NEUTRALIZATION
109
109
5.1
NEUTRALIZATION BELOW VHF
109
5.2
PUSH-PULL NEUTRALIZATION
111
5.3
SINGLE-ENDED NEUTRALIZATION
111
5.4
NEUTRALIZING GROUNDED-GRID AMPLIFIERS
113
5.5
NEUTRALIZATION PROCEDURE
5.6
SELF-NEUTRALIZING FREQUENCIES OF
TETRODES AND PENTODES 120
SECTION 6
117
125
OPERATING CONDITIONS
125
6.1
ADJUSTMENT OF LOADING AND EXCITATION
125
6.2
OPERATING VOLTAGES AND CURRENTS 126
6.3
EFFECT OF DIFFERENT SCREEN VOLTAGES
127
vii
6.4
THE THREE HALVES POWER LAW
127
6.5
BALANCE OF AMPLIFIERS
6.6
HARMONIC AMPLIFIER AND CONTROL OF
HARMONICS
130
6.7
SHIELDING 133
6.8
DRIVE POWER REQUIREMENTS
6.9
VHF AND UHF OPERATING CONDITIONS FOR
SATISFACTORY ANODE EFFICIENCY AND
MINIMUM DRIVE 137
6.10
COOLING TECHNIQUES
6.11
TUBE LIFE 162
128
135
137
BIBLIOGRAPHY
168
Index
169
viii
Illustrations
Figure 1:
Figure 2:
Figure 3:
Figure 4:
Figure 5:
Figure 6:
Figure 7:
Figure 8.
Figure 9.
Figure 10:
Figure 11:
Figure 12:
Figure 13:
Figure 14:
Figure 15:
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Figure 17:
Figure 18:
Figure 19:
Figure 20.
Figure 21:
Figure 22:
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Figure 28.
Figure 29.
Figure 30:
Figure 31:
Figure 32:
Figure 33A.
Figure 33B.
Figure 34.
Figure 35.
Figure 36.
Figure 37.
Figure 38.
Figure 39A.
Figure 39B.
Figure 40.
Figure 41.
Figure 42:
Figure 43.
Constant current curves for 3CX3000A1 (µ = 5). .......................... 5
Constant current curves for 3CX3000A7 (µ = 160). ...................... 5
Constant current curves for a zero-bias triode with a µ of 200...... 6
Internal configuration of a planar triode. ........................................ 7
Incorrect screen circuit for tube. .................................................. 10
A correct screen circuit for tube. ...................................................11
Another approach to swamping the screen circuit. ......................11
Typical curve of grid current. ....................................................... 12
Secondary-emission characteristics of the metals. .................... 13
Eimac K2 IOT Amplifier .............................................................. 17
Eimac K2 Inductive Output Tube ................................................. 19
Typical tuning curves for UHF TV IOT. ........................................ 21
Equipotential lines in a three stage collector.. ............................. 22
Electron trajectories at near to ideal power. ............................... 23
Electron trajectories at higher than ideal power.. ........................ 23
Typical MSDC IOT power supply schematic ............................... 24
Pulse derating curve................................................................... 25
Typical oxide cathode. ................................................................. 26
Typical bar tungsten filament....................................................... 27
Typical mesh tungsten filament. .................................................. 27
Typical Focus Cathode (LPT-62) ................................................. 28
Tungsten Matrix (Dispenser) Cathode......................................... 29
Anode efficiency vs. Conduction angle. ...................................... 36
Variation of anode and grid voltage ............................................. 38
Anode voltage and grid voltage scales........................................ 39
Instantaneous values of anode and grid current. ........................ 40
Constant current characteristics for 4CX20,000A/8990 tetrode. . 40
Constant current characteristics for 4CWI00,000D tetrode. ........ 50
A typical circuit for an RF amplifier. ............................................. 52
Relative harmonic vs. Resonant circuit Q. .................................. 53
Determination of input capacitor C1. ........................................... 53
Determination of loading Capacitor C2. ...................................... 54
Determination of Inductor L ......................................................... 55
Reactance of an RF choke vs. Frequency................................... 56
A typical circuit using “zero-bias” triodes. .................................... 63
A typical circuit using “Zero-bias” triodes..................................... 64
3CX5000A7 with integral grid flange ........................................... 64
Tetrode and pentode protection chart.......................................... 66
Triode protection chart................................................................. 67
Screen voltage control circuit for exciter keying. ......................... 71
A typical method of keying a tetrode or pentode amplifier. .......... 72
Basic screen and anode modulation circuits. .............................. 73
Usual circuit supporting VHF parasitic oscillation........................ 78
Placement of parasitic suppressors. ........................................... 79
Relative spectrum space occupied by AM and SSB signals. ...... 84
ix
Figure 44.
Figure 45.
Figure 46.
Figure 47.
Figure 48.
Figure 49.
Figure 50.
Figure 51.
Figure 52.
Figure 53.
Figure 54.
Figure 55.
Figure 56.
Figure 57.
Figure 58.
Figure 59.
Figure 60.
Figure 61.
Figure 62.
Figure 63.
Figure 64.
Figure 65.
Figure 66.
Figure 67.
Figure 68.
Figure 68A.
Figure 69.
Figure 70.
Figure 71.
Figure 72.
Figure 73.
Figure 74.
Figure 75
Figure 76.
Figure 77.
Figure 78.
Figure 79.
Figure 80.
Figure 81.
Figure 82
Figure 83.
Figure 84.
Figure 85.
Figure 86.
Figure 87.
Figure 88.
R-F output of SSB transmitter with single-tone modulation......... 85
Spectrum of SSB transmitter modulated by two-tone signal. ...... 86
Spectrum of SSB transmitter modulated by 1500-Hz tone.......... 86
R-f output of SSB transmitter modulated by two-tone signal....... 87
Single-tone condition. .................................................................. 89
Two-tone condition. ..................................................................... 91
Three-tone condition. .................................................................. 91
Spectrum at the output of a non-linear device............................. 95
Ideal grid-anode transfer curve for Class AB operation............... 97
Block diagram of Intermodulation Distortion Analyzer ................. 98
Intermodulation distortion products may be predicted............... 100
IM Distortion Test Data for EIMAC 4CX1500B (EC2 = 225V) ... 102
IM Distortion Test Data for EIMAC 4CX1500B (EC2 = 25OV) .. 103
Wire neutralizing system. ...........................................................110
Push-pull grid neutralization, basic circuit. ................................. 111
Single-ended grid neutralization. ................................................ 111
Single-ended anode neutralization, basic circuit. .......................112
Single-ended anode neutralization . ...........................................113
Neutralization of a symmetrical grid-excited amplifier. ...............115
Neutralization by cross-connected capacitors. ...........................115
Neutralization by cross-connected capacitors. ...........................116
Circuit of grounded-grid amplifier. ..............................................117
Tetrode characteristics involved in feedback circuit. ..................119
Graphical presentation of components of output circuit. ............119
Components of output voltage of a tetrode. .............................. 122
Components of output voltage of a tetrode. .............................. 123
Components of output voltage of a tetrode. .............................. 123
Three-halves power of commonly-used factors. ....................... 128
Anode-Current Pulse Length and Power Output. ...................... 131
Typical air cooling system. ........................................................ 139
Tube mounting providing cooling, shielding and isolation. ........ 140
Chassis mounting providing cooling, shielding and isolation. ... 140
Example of a badly overheated tetrode..................................... 141
Measuring back-pressure24. ..................................................... 141
Cooling Airflow Requirements ................................................... 143
Combined correction factors for land-based installations.......... 146
Conversion of mass airflow rate to volumetric airflow rate. ....... 147
Typical vapor-phase cooling system. ........................................ 152
EIMAC vapor-cooled tubes for mounting in boilers. .................. 152
Cutaway of “classic” boiler and tube combination. .................... 153
Cutaway view of typical Control Box. ........................................ 154
Typical 4-tube vapor cooling system. ........................................ 155
Cutaway of pressure equalizer fitting. ....................................... 156
Typical 4-tube system using “steam-out-the-bottom” boilers..... 156
Cutaway view of “steam-out-the-bottom” boilers. ...................... 159
Useful conversion factors. ......................................................... 161
x