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EHRHORN ALPHA 77Sx Operating And Technical Manual

High frequency linear power amplifiers
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PRICE: $10.00
OPERATING A N D T E C H N IC A L M A N U A L
HIGH FREQUENCY LINEAR POWER AMPLIFIERS
ALPHA 77Dx and ALPHA 77Sx
EHRHORN TE C H N O LO G IC A L OPERATIONS, INC.
JANUARY 1990

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  • Page 1 OPERATING A N D T E C H N IC A L M A N U A L HIGH FREQUENCY LINEAR POWER AMPLIFIERS ALPHA 77Dx and ALPHA 77Sx EHRHORN TE C H N O LO G IC A L OPERATIONS, INC. JANUARY 1990...
  • Page 2 IMPORTANT SERVICE ASSISTANCE To help you secure technical assistance without wasted long distance calls, ETO has established a special SERVICE telephone line WHICH WILL BE ANSWERED ONLY WHEN A QUALIFIED SERVICE TECHNICIAN IS AVAILABLE TO HELP YOU IMMEDIATELY. The special service number is (719) 599-3861. If your call to this number is NOT answered it indicates that no qualified technician is free to talk with you at the moment.

  • Page 3: Table Of Contents

    Schematic, QSK Circuit Board CB-3 ..SECTION 6 - STANDARD ELECTRICAL PARTS L I S T ..... ET0/"ALPHA" PRODUCT WARRANTY ... Outside Back Cover EHRHORN TECHNOLOGICAL OPERATIONS, INC. 4975 NORTH 30TH STREET COLORADO SPRINGS, COLORADO 80919 U.S.A. REV. 1/90 @ U.S.A.

  • Page 4: Section 1 - General Description

    Net weight & 95 lb. (43 kg), shipping weight (57 kg) in two cartons. VARIATIONS FOR GOVERNMENT/EXPORT-ONLY MODEL ALPHA 77Sx (PA-77Sx)t Same as ALPHA 77Dx (PA-77Dx) above except two 8877 tubes permit greater PEP input and output power. Approximately 175 watts drive for maximum output.

  • Page 5: Section 2 - Installation

    SECTION 2 T N S T A L L A T T ON 1. Unpacking: Carefully remove amplifier and transformer from car­ tons; SAVE ALL PACKING MATERIAL FOR RE-USE — SHIPMENT OF ALPHA 77DXIN OTHER THAN FACTORY PACKING MAY RESULT IN DAMAGE NOT COVERED UNDER WARRANTY ©£©...
  • Page 6 #7 at the back. The standard wiring to TS-1 (for 120/240V with center neutral) is as follows* (See Fig. 1, page 4) LUG 1 — Ground (mounting foot for terminal strip) LUG 2 — White/black wire LUG 3 — White wire LUG 4 —...
  • Page 7 Figure 2: TS-1 wiring modified Figure 1: Standard TS-1 wiring for 120V or 120/240V AC mains. for 240V without center neutral. (See also Figure 4.) (rear) gray wires (mtg.) gray wires ( z f c black wire black wire wh/vio., blower w .

  • Page 8: Rf And Control Connections

    5. RF And Control Connections: Interconnection of the ALPHA 77Dx (or 77S$ with any popular transceiver or exciter for conventional PTT, VOX, or manually-controlled T/R operation is straightforward. Special provisions are incorporated for full CW break-in or fast VOX operation with transceivers/exciters so equipped. Rear panel connections and functions are as follows: RF INPUT - Use a standard "BNC"...
  • Page 9 closure which follows the keying imposed externally on the RELAY jack,with one restraint: the output KEY line does not close until the amplifier's internal changeover relay contacts have actually closed. The KEY line opens immediately, however, when the input line to the RELAY jack is opened. When the amplifier is in OFF or STANDBY, the RELAY jack is connected through to the KEY jack.
  • Page 10 Figure 7» ALPHA 77Dx(77Sd Interconnections for VOX or PTT x c v r x m t r ¿1C ¥ R G rS A /U R G -S 8 C / U 75 A N T . | ___ < "P H O rJd ' T Y P E Figure 8»ALPHA 77Dx(77Sd Interconnections for CW Break-In or Fast VOX (Also suitable for PTT, Manual T/R, etc.) k s z a y...

  • Page 11: Section 3 - Operation

    SECTION 3 OPERATION 1. Control Functions: MODE CONTROL PUSH BUTTONS - These four buttons to the right of the AVERAGE PLATE CURRENT meter control AC power on-off and the operational mode of the ALPHA 77Dx(77S$. OFF - Push to remove all AC power from amplifier. This button illuminates when all four MODE buttons are out as a result of tripping of the plate overcur­...

  • Page 12: Tune-Up Procedure

    TUNE - Controls the plate tuning (vacuum variable) capacitor. Capacitance is maximum (lower frequency bands) at full counterclockwise rotation and minimum (higher frequency) at full clockwise (see also paragraph 1, page 2). BAND - Selects appropriate amplifier tuning range, as indicated (in MHz) on the dial skirt.
  • Page 13 (d) INITIAL TUNE-UP - Insure that the amplifier is properly in­ stalled in accordance with Section 2 and that a suitable, matched load is connected. (1) Place all four MULTIMETER buttons in the out position by momentarily depressing any button half-way, so that meter indicates HV.

  • Page 14: Final Operational Adjustments « S C Monitoring

    IF AT ANY POINT IN THE FOLLOWING PROCEDURES THE AMPLIFIER DOES NOT RESPOND AS EXPECTED, REMOVE EXCITATION IMMEDI­ ATELY AND CORRECT THE PROBLEM BEFORE CONTINUING! ) Switch exciter to "tune” or "lock key" condition and very slowly increase its output while watching the amplifier GRID and PLATE meter indications.

  • Page 15: 4. Operating Notes

    (c) HIGH POWER SSB/VOICE - After initial tune-up as described, pressing the amplifier "5SB/HIGH V" button increases plate voltage about 5°%> preparing the amplifier for SSB/voice operation at PEP power inputs of approximately 2.0 to 2.5 times the tune-up power level. It is necessary to switch the exciter to SSB and adjust its output exactly as described in the previous paragraph (b) for the specified grid current.
  • Page 16 TUBE RATINGS - The 88?? is extremely rugged and operates with a large safety margin if grid current is never allowed to exceed 0.2 ampere, nor plate current 1.0 ampere, per tube. Also, it is exceedingly important to insure that cooling air­ flow is never interrupted or blocked.

  • Page 17: Troubleshooting Hints

    The amplifier interior, particularly the high voltage d-c areas of the power supply and rf compartment, should " b e cleaned frequently enough (with a soft brush and a vacuum cleaner) to prevent visible accumulation of dust. If ex­ tremely dusty conditions prevail, it may be advisable to secure across the air intake area a thin plastic air filter, of the type commonly used in window air conditioners.
  • Page 18 a) Excessive load VSWR; mismatched 9. RF flashover (usually between loading capacitor plates) in or wrong antenna; defective rf rf compartment. cables; antenna breaking down. b) Antenna relay K5 damaged. c) Capacitor plates damaged by re­ peated arcing as above. 10.

  • Page 19: Section 4 - Theory Of Operation

    SECTION 4 THEORY OF OPERATION 1. 8877 RF Amplifier Circuitry! (Refer to Fig. 18) The 8877 triode tube (two, parallel-connected, in ALPHA 77S) is connected in grounded-grid for high stability, linearity, and simplicity. Bandswitch S2 and associated components provide pre-tuned input circuits to optimize performance on each amateur band from through 15*foeters (or other frequency ranges if appropriately readjusted).
  • Page 20 Transformer T1 provides all a-c voltages required for operation of the amplifier. High voltage tap-change relay K3, controlled by S5, selects either of two high voltage secondary taps, yield­ ing d-c operating high voltage of approximately 2500 V or 3900 V at no load.
  • Page 21 The +24V DC Supply consists of rectifier D214, filter capacitor C211, and integrated circuit voltage regulator MC7824. Capacitor insures regulator stability, and C209 improves output regu­ lation under transient load conditions (as when switching K 77 tube receives cathode bias from the +50 V supply con­ sisting of D215 and C212.
  • Page 22 A somewhat higher voltage (the drop across both R203 and R204 in series) is stored with a shorter time constant established by C201/R205• When plate current drops to a lower level, the voltage across C202 remains relatively constant at its peak value until C201 discharges to a voltage slightly lower than that across C202, at which point C202 also begins discharging through D202 and R205 at a relatively rapid rate.
  • Page 23 zero when the key contacts (RELAY line) are closed, and (2) via R311. The bias supplied via R 3 H is shorted to ground via the N.O. (transmit-side) contacts of main T/R relay K5 when they close; the path is via pin 7 of CB chassis harness wiring and feed-thru capacitor C to the rf deck area, and finally via L13»...

  • Page 24: Section 5 - Illustrations

    S E C T IO N 5 — IL L U S T R A T IO N S F IG U R E 9 - F R O N T P A N E L A V E R A G E P LATE C U R R E N T M ETER FIGURE 10 - BACK PANEL f~RF O UTPUT \ ..

  • Page 25: Front Sub-Panel; Back Side Of Front Panel

    F IG U R E 11 - Front Sub-Pa ne l (M ain Front Panel Rem oved) iD13-D16~* SC R E W .BAN D D R IV E ? - 2 2 -...

  • Page 26: Rf Section, Top And Side, Covers Removed

    FIGURE 13 - Top View RF Compartment (Cabinet Cover, Inner RF Shield, and Hot Air Exhaust Duct Removed) FIGURE 14 - Side View RF Compartment (RF Side Shield Removed) WATT M ETER- - 2 3 -...

  • Page 27: Power Supply Section, Side And Oblique

    F IG U R E 15A - Pow er S u p p ly Sid e View (T1 Transfo rm er Rem oved) - 2 4 -...
  • Page 28 F IG U R E 16 - U nderside of Tube D e c k (C o ve r Plate Rem oved) B A N D INPU T CAP. 053/054"* 160 ..FIGURE 17 - Circuit Board CB2 ...C 55| 30 ..

  • Page 29: Tube Deck, Underside; Circuit Board Cb-2 . „ . 25 Circuit Board Cb-3; Wattmeter

    C IR C U IT B O A R D C B 3 - 2 6 -...
  • Page 30 R X A N T L 8 9 0 J ll S8 R £ O E T . T H R U P R E -K 4 R I IZ K /2 W A U X .001 C 1 4 -^/VW—...

  • Page 31: Sschematic,Hematischematic,, Rf Seschematic,Tion & Tube D E Schematic, K

    N O T USED LOWER RF ENCLOSURE UNDER RF OECK ) (-------) ( -c9-i PWR ( CONTROL AREA FIG. 10: A L P H A 77D & SCHEMATIC-RF SECTION « > EHRHORN TECHNOLOGICAL OPERATIONS, INC. -27- CANON CITY, CO. 81212 REV: 5-77...

  • Page 32: Schematic, Front Panel

    (TO P5) N E U T w h i o r g I 0 / 2 5 W 2 A(SB) (3A.SK) PINS 14 THRU 19 MAYBE PINS I THRU 6 OF J 6 FIG 19: ALPH/> OLDER M O DELS EHRHORN...
  • Page 33 7 7 S X ' 4 - IKI4722 S E R I E S CB 2 WHI/ORG FIG 19: ALPHA 77D & 77S SCHEMAT IC - POWER SUPPLY & M AIN CHASSIS EHRHORN TECH. OP*NS, INC. CANON CITY, CO. 51212 REV; 5 - 7 7...

  • Page 34: Schematic, Qsk Circuit Board Cb-3

    m ode s w i t c h (TYP) HV RELAY + 2 4 V D C O U T PINK S5 F S T B 2 A \ / D C T P I + ^ 0 0 * 1 M ETE R LAM PS W D 3...

  • Page 35: Section 6 - Standard Electrical Parts L I S T

    U N ITS ONLY) W H I / H24V B R N © © © © © FIG. 20: ALPHA 7 7 D 1 7 7S SCHLMAT IC - FRONT PANEL EHRHORN TECH. OP’NS, INC. CANON CITY, CO. 81212 REV: 5-77...
  • Page 36 ☆ R E L A Y S SHOWN IN OFF P O S I T I O N S R 21 5 EHRHORN TECHNOLOGI CAL O P E R A T I O N S , — A / W CAÑON...
  • Page 37 M XFMR TO R F FROM Q S K TO SWI TCH TO R S . P C B i ( P R I M A R Y A ( T O C I ) ( J I O - P I N 2) ( J 5 - P I N 9) N E U T R A L ) PL UG- I N...
  • Page 38 FIG. 2 2 : ALPHA 7 7 D & 7 7 S SCHEMATIC - CB3 (QSK BOARD) EHRHORN TECHNOLOGICAL OPERATIONS, INC 4. A L L C A P A C ITO R S IN CANON CI T Y, CO. 81212 REr .
  • Page 39 S E C T I O N 6 - S T A N D A R D E L E C T R I C A L PARTS S Y M B O L D E S C R I P T I O N S Y M B O L D E S C R I P T I O N RF S E C T I O N...
  • Page 40 T H IS W ARRANTY POLICY IS C L A S S IF IE D AS A L IM IT E D W ARRANTY.) EHRHORN TEC H N O LO G IC A L OPERATIONS, INC. 4975 North 30th Street Colorado Springs, Colorado 80919 U.S.A.

This manual is also suitable for:

Alpha 77dx

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