Alpha Power ETO 91B User Manual
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Alpha Power ETO 91B User Manual

Hf linear power amplifier
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U
HF LINEAR POWER AMPLIFIER
Q i b u n
A L F H A / p o w E R >
I l L i n B
14440 Mead Court, Unit B, Longmont, Colorado 80504
p p | 4 * * (970) 535-4173 * FAX (970) 535-0281
'
M
s e r
s
IN C
RF Power for Communications and Industry
a n u a l

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  • Page 1 ’ s e r a n u a l HF LINEAR POWER AMPLIFIER Q i b u n A L F H A / p o w E R > IN C RF Power for Communications and Industry I l L i n B 14440 Mead Court, Unit B, Longmont, Colorado 80504 p p | 4 * * (970) 535-4173 * FAX (970) 535-0281...

  • Page 2: Table Of Contents

    CONTENTS CRITICAL PRECAUTION DURING INSTALLATION Section 1 INTRODUCTION General Description of the ETO 91/3 Amplifier Specifications, ETO 91/3 Figure 1 Top View Section 2 PREPARING THE ETO 91fi FOR OPERATION Transformer Installation Inspection of Tubes & Chimneys AC Primary Connections & Amplifier Grounding Operation from 90-130V mains Figures 2-4 Transformer Installation Section 3 AMPLIFIER/STATION INTERCONNECTIONS...

  • Page 3: Critical Precaution During Installation

    IMPORTANT CRITICAL PRECAUTION DURING INSTALLATION OF YOUR ETO 31/?! While the cover is removed to install the power transformer, make sure that the tubes are properly installed as described in Section 2 below. Failure to do this may cause severe dam­ age or destruction of both tubes.
  • Page 4 C21-C24 (C26 under) Power Supply Board PS/J1...

  • Page 5: Figure 1 Top View

    HV Crowbar Vacuum Relay Power Relays P1/XFMR S3 Interlock Figure 1 Top View...
  • Page 6 Output Impedance: 50 ohms unbalanced. Maximum Load VSWR: 2:1 at full rated power output. VSWR Trip: Automatic standby when reflected power >250 watts. Intermodulation Distortion: 36 dB below rated output. Harmonic Output: < -55 dBc. Tubes: Two Svetlana 4CX800A/GU74b ceramic-metal tetrodes. Cooling: Full-cabinet, ducted forced air using cushion-mounted centrifugal blower.

  • Page 7: Transformer Installation

    Section 2 91ß PREPARING THE ETO FOR OPERATION Transformer Installation (See Figures 2-4) Remove the amplifier top cover to install the transformer. Only one possible transformer orientation allows mating all its connectors without straining leads. Lift the transformer high enough to dear the right side chassis lip and move it sideways into the chassis. USE CAU­ TION! PROCEED SLOWLY to avoid damaging wires or components.

  • Page 8: Operation From 90-130V Mains

    tacles for 200-240V circuits. ALWAYS use grounding type AC connectors which conform to local codes and ensure that the green/yellow wire in the 91 fi power cable is wired only to the AC mains safety ground (or to neutral, as may be necessary with a 240V circuit config­ ured 120V-N-120V without a separate ground, commonly found in the US).

  • Page 9: Figures 2-4 Transformer Installation

    AC CONNECTION H V CONNECTION V I E W A - A CONNECTIONS V I E W A - A V I E W A - A HIGH AND LOW V O L T A G E BOARD CONNECTIONS FIGURES 2-4 91 ß...
  • Page 10 FIGURE 5 91B REAR PANEL...

  • Page 11: Section 3 Amplifier/Station Interconnections

    Section 3 AMPLIFIER/STATION INTERCONNECTIONS (See Fig. 5) Coaxial Cable Types & Connectors Connect the transceiver RF output to the ETO 91(3 RF INPUT with 50 ohm coaxial cable - RG-58C/U or equivalent Use "UHF" type plugs, such as Amphenol 83-1SP, with reducing adapter to fit RG-58.

  • Page 12: Section 4 Operation

    Section 4 OPERATION 4.1 Control Functions (See front cover photo) BAND - Use to select amateur band desired (in MHz). TUNE - Selects operating frequency. Higher frequencies tend to tune toward the "0" end of the dial scale, while lower frequencies tend to tune further toward the "100" end. LOAD - Sets amplifier plate loading and determines the power level at which best efficiency and linearity are achieved.

  • Page 13: Turning On The Amplifier

    Any linear amplifier must be adjusted for optimum efficiency and linearity at a specific power level. If operation at higher power is then attempted without appropriate readjust­ ment, the result will be flattopping, "splatter," and (usually) excessive amplifier grid current. If operated at a much lower power level than it has been adjusted for, the amplifier's effi­...

  • Page 14: Tuning Up For Operation At 1,500 Watts Rf Output

    If any of the following does NOT occur, depress power OFF switch immediately and investi­ gate before proceeding: * The blower starts (note air exhausting above tubes. * The multimeter bargraph automatically displays HV; it should indicate approximately 2.8 KV. * The WATT LED is lighted.

  • Page 15: Reflected Power Protection

    5) Switch transceiver to CW and increase its carrier output to approximately 15 watts (9Iß output approx. 300-500 watts). NOTE! If more than about 15 W drive is applied while the 91ß is substantially mistuned, the 9 lß will switch to STBY. If the amplifier is returned to receive (key-up) it will automatically reset to OPR in about 4 seconds.

  • Page 16: Section5 Operating And Maintenance Notes

    Section 5 OPERATING AND MAINTENANCE NOTES TUBES - The 4CX800A / GU74b tubes used in the ETO 91/3 are very rugged and normally operate with a large margin of safety. They should provide outstanding service for many years if not damaged by abuse- especially overdrive or blockage of cooling airflow. Allow at least twelve inches (31 cm) unobstructed clearance around the air intake and exhaust areas.

  • Page 17: Plate Overcurrent Relay

    DAMAGE RESULTING FROM USE OF A FUSE OF INCORRECT SIZE OR TYPE WILL NOT BE COVERED UNDER WARRANTY AND MAY VOID THE WARRANTY. PLATE OVERCURRENT RELAY — This relay will quickly turn off the amplifier in the event of grossly excessive plate current or fault in the high voltage circuitry. The relay will not prevent tube or other damage due to either short or long term overdrive or improper tuning.

  • Page 18: Section 6 Troubleshooting Hints

    Section 6 TROUBLESHOOTING HINTS A) 91/3 will not turn on; nothing happens when ON switch is pushed. 1) External AC wiring, fuse or circuit breaker may be open. 2) Amplifier cover not in place; cover safety interlock open. 3) Fuse F1-F4 open or missing; check fuses with an ohmmeter. 4) Step-start resistor R6or R7 open.
  • Page 19 1) RELAY (T/R) control cable from transceiver is shorted. 2) Transceiver locked in transmit. I) Plate current indicated when amplifier is in STBY or receive. 1) 4CX800A/GU74b tube heater-to-cathode leakage or short. 2) Tube bias supply or T/ R bias switch faulty. P Distorted SSB signal;...

  • Page 20: Section 7 Design And Circuit Overview

    Section 7 91fi DESIGN AND CIRCUIT OVERVIEW RF Amplifier Section (See Figure 6,11) Two 4CX800A / GU74b tubes are employed in a grounded-cathode, grid-driven circuit. Excellent linearity is achieved by operating the tubes as tetrodes with normal control grid (Gl), screen grid (G2), and plate (anode) DC voltages. Drive voltage required under these conditions is low enough to permit using an untuned input loaded by non-inductive 50 ohm resistor R l.
  • Page 21 Control Circuits (Figure 7) Control and monitoring circuits are grouped on the Control Board, which is physically located on the front of the 9 lß subpanel. Generally, monitoring and protective functions are clustered on the left side of the schematic, warm-up and status indicator functions at lower right, and keying/switching functions at upper right.

  • Page 22: Schematics

    91fi SCHEMATICS...
  • Page 23 iaa-ieavA C 2 0 0 - 2 5 0 V A C — □ sL _ & _ XXXXX C O N T R O L B U S S 9 0 - 1 1 0 V...
  • Page 24 ± ± - L 1 2 1 n H y J 3 > — ^ C O I L O U T P U T W A T T L 10 C 2 0 A P C B M E T E R 1 0 / 4 0 m 8 0 / l 6 0 n C O I L...
  • Page 26 B R E A K D 2 3 U N L O C K 10 M E T E R S FIGURE 7 91 ß CONTROL BOARD...
  • Page 27 H E A P E R 10x2 F V D G U T L E P ~ > -C 1 : P E A K MAX □ U T ~c 3 : R E F L . M E T E R □...
  • Page 28 FIGURE 8 91/S DISPLAY BOARD...
  • Page 29 FIGURE 9 91 ß POWER SUPPLY BOARD...
  • Page 30 FIGURE 10 91/3 HV FILTER & SCREEN SUPPLY...
  • Page 31 FIGURE 11 91 ß INPUT BOARD...
  • Page 32 FIGURE 12 91 ß OUTPUT RF WATTMETER FIGURE 13 91 ß MULTIMETER SWITCH...

  • Page 33: Alpha Products Warranty

    ALPHA PRODUCTS WARRANTY ALPHA/POWER, INC. (API) W A R R A N T S AS F O L L O W S E A C H N EW A M A T E U R R A D IO P R O D U C T O F IT S M A N U F A C T U R E , S O L D AND U SE D IN T H E U N IT E D S T A T E S , IT S P O S S E S S IO N S , AND C AN AD A: Workmanship and all components except rf power tubes are warranted for FOUR YEARS from date of original purchase if used exclusively in licensed amateur radio service.

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