Alpha Power ETO 91B User manual

Us e r ’s M a n u a l
HF LINEAR POWER AMPLIFIER
Qi bun ALFHA/powER>IN C RF Power for Communications and Industry
IlLinB 14440 Mead Court, Unit B, Longmont, Colorado 80504
p p | 4 ** ( 70) 535-4173 * FAX ( 70) 535-0281

CONTENTS
CRITICAL PRECAUTION DURING INSTALLATION 1
Section 1 INTRODUCTION 1
General Description of the ETO 91/3 Amplifier 1
Specifications, ETO 91/3 1
Figure 1 Top View 3
Section 2 PREPARING THE ETO 91fi FOR OPERATION 4
Transformer Installation 4
Inspection of Tubes & Chimneys 4
AC Primary Connections & Amplifier Grounding 4
Operation from 0-130V mains 5
Figures 2-4 Transformer Installation 6
Section 3 AMPLIFIER/STATION INTERCONNECTIONS 7
Coaxial Cable Types & Connectors 7
T/R Control Cable 7
ALC 7
Figure 5 Back Panel 8
Section 4 OPERATION
4.1 Control Functions
4.2 Tune-up
1. Turning On the Amplifier 10
2. Tuning Up for Operation at 1,500 Watts RF Output 11
4.3 Reflected Power Protection 12
4.4 ALC 12
Section5 OPERATING AND MAINTENANCE NOTES 13
Tubes 13
Fuses 13
Electronic Bias Control 14
Plate Overcurrent Relay 14
Preventive Maintenance 14
Section 6 TROUBLESHOOTING HINTS 15
Section 7 DESIGN AND CIRCUIT OVERVIEW 17
SCHEMATICS 1

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. Such damage is not covered under warranty.
CAUTION: Only the screws securing the 91/3 top cover and front panel have ENGLISH
threads (6-32 or 8-32). ALL OTHER HARDWARE IS METRIC DO NOT REPLACE
TRANSFORMER OR OTHER SCREWS WITH ENGLISH SIZES, as doing so will damage
the captive nuts installed in the chassis.
Section 1
INTRO UCTION
General Description of the ETO 91fi Amplifier
The ETO 91/3 is a self-contained, HF linear power amplifier capable of continuous operation
at 1500 watts peak power output on SSB, keyed CW, SSTV, RTTY, digital modes or AM, with
no time limit. If periods of "con tinuous-key-dcrwn" carrier operation will exceed 5 minutes, t e
optional auxiliary cooling fan available from ETO must be installed to avoid possible damage not
covered by t e warranty.
As shipped, units delivered within the USA and its territories are manually tunable to cover
all HF amateur bands from 1.8 to 14.35 MHz, with extensive out-of-band capability for
operation on MARS, etc. Appropriately-licensed users may contact ETO for information
on modifying domestic amplifiers to extend coverage to 2 .7 MHz.
Specifications, ETO 91fi
Frequency Coverage: U.S. units only, amateur bands 1.8-14.35 MHz as shipped (see note
above); export units, 1.8-2 .7 MHz.
Power Output 1500 watts peak all modes, including SSB, CW and continuous or modulated
carrier. Carrier operation (eg., AO, RTTY or FM) for more than 5 minutes at or near maxi
mum rated power requires use of the auxiliary cooling fan accessory.
Drive Power 50 to 60 watts nominal for rated output.
Power Gain: Nominally 14 dB, a power increase of 25 times.
Input Impedance: 50 ohms nominal, unbalanced; VSWR <1.5:1.
1

C21-C24
C20
(C26 under)
Power
Supply
Board
PS/J1 J2

L4
BL1
HV Crow ar
Vacuum Relay
Power
K2 Relays
P1/XFMR
Ti
S3 Interlock
Figure 1
9ip Top View

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.
Automatic Level Control (ALC): Negative from 0, adjustable.
Primary Power: 200/220/240 or 100/120 VAC nominal, 50-60 Hz, fused at 20 amperes.
Power Transformer. 3+ kVA with strip-wound Unisil-H(R) core.
Protective Functions: Primary and step-start fuses, primary AC interlock, high voltage
crowbar, peak and average plate overcurrent trip-outs, arc protection trip, reflected power
trip, grid current limiting & sustained overdrive trip.
Status Indicators: ON, WATT (initial tum-on time delay), OPERATE and FAULT LEDs.
Metering: Dedicated, full-time LED bar graphs display forward and reflected rf power; grid
current LEDs; LED bargraph selectable among plate voltage, plate current, and tune-up
functions.
Size: 7.5" H x 17' W x 15.5" D (1 x 43 x 3 cm).
Weight: 66 lb. (30 kg) net, 75 lb (34 kg) ship; two cartons.
Note: ETO reserves the right to change design and/or specifications without prior notice or
obligation.
2

Section 2
PREPARING THE ETO 91ß 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. From underneath,
insert the supplied bolts with washers through the clearance holes in the chassis and into the
nuts in the transformer base. CAUTION! Mate transformer connectors carefully and gently
to insure that all connector pins engage correctly and fully.
Inspection of Tubes & Chimneys
While the top cover is removed, make sure tubes are firmly seated in their sockets, rubber
exhaust chimneys are fully and correctly installed, and anode connectors are tightly clamped
to tubes.
The silicone rubber chimneys installed on the 4CX800A/ GU74b tubes are absolutely essential
parts of the cooling system. Make sure the chimneys are straight and fully installed so that
the bottom of each chimney is firmly against the tube deck and completely covers the airflow
openings in the deck. Tube cooling air must exit only through the tube anode fins; it must not
be allowed to escape outside them. Failure to ensure proper cooling airflow may result in
tube damage or destruction which is not covered under warranty.
AC Primary Connections & Amplifier Grounding
Primary voltage taps are selected at the terminal strip numbered "1" to "7" and located on
the chassis center divider, left of and above the transformer. Connect the two wires labeled
"A" and "B" for the line voltage to be used, as shown in the following table. The two short
jumper wires supplied are not used on 200-250V, but must be connected as shown for opera
tion on 100-120V mains.
PRIMARY "A" to terminal
4 (factory setting)
"B " to terminal Tumpers
Not used for
1 0 to 250V
230-250V
210-230V
1 0-210V
110-130V
0-110V
4
5
4
5
2
3
3
6
6
operation
1 -> 2,6 -> 7
1 -> 3,6 -> 7
Power Cord Connections — WARNING!
To avoid hazard of potentially fatal electric shock and/or severe damage to the ETO 91fi
and other equipment, always use an AC plug which is appropriate for the primary mains
voltage, current rating and configuration. NEVER use 120V-type plugs and power recep-

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).
The green/yellow conductor in the power cord is wired to the ETO 91/3 chassis. It MUST be
connected only to the power source safety ground or neutral. The blue and brown power
cord wires connect to the two "hot" wires of the AC source; either wire may be connected to
either side of the line. For best results use a dedicated 200-240V branch circuit of #10 AWG
copper wire or equivalent, rated at 20A, to feed the amplifier.
Important information concerning operation from 0-130V mains
Electrical power equipment will draw twice as much primary current from 120V mains as
from 240V mains. Therefore, operating t e ETO 91/3 on a typical 120V¡20A ouse old circuit
wit out exceeding t e 20A circuit rating will limit maximum peak power output to about 600-1000
watts. Maximum possible RF output power for any particular primary AC voltage and cur
rent capacity may be estimated as
Po max = (Vline x Dine) / 2.3.
For example, if the 91(3 operates from a circuit which is capable of delivering 115VAC at a
maximum current of 20A, with no other loads connected to the circuit maximum peak RF
output possible without tripping the 20A breaker (or fuse) is approximately
Po max = (115V x 20A) / 2.3 = 2300/2.3 = 1000 watts.
If the same circuit also supplies a transceiver drawing peak line current of 5A and a lamp
drawing 1 A, only 20-5-1 = 14A is available for the amplifier and maximum possible output is
about
Po max = (115V x 14A) / 2.3 = 1610/2.3 = 700W.
RF Grounding
A ground stud with wing nut is provided on the rear of the chassis. Connection should be
made from this stud to a good RF earth ground, such as a copper water pipe or driven rod,
via heavy copper braid or strap. CAUTION: W en using any ig power amplifier, failure to
connect ALL station equipment to a good common ground may allow RF feedback to leak into t e
transceiver and cause severe signal distortion.
Replacing the Amplifier Cover
Use only the 6-32 screws supplied with the amplifier and do not tighten any of the screws
until all are started.
5

3A
AC CONNECTION
VIEW A-A
HIGH AND LOW VOLTAGE BOARD CONNECTIONS
HV CONNECTION
VIEW A-A
LV CONNECTIONS
VIEW A-A
FIGURES 2-4
91 ß TRANSFORMER
INSTALLATION

FIGURE 5
91B REAR PANEL