AMERITRON AL-1200 Operation manual

FULL POWER LINEAR AMPLIFIER

INSTRUCTION MANUAL

The Ameritron AL-1200 is a 1500 watt output linear amplifier that operates from 160 through 15 meters. The Ameritron AL1200X is the export model and covers 160 throug h 10 meters. The AL-1200 uses a single 3CX1200A7 tube in a class AB2 grounded grid circuit. CW, FM and RTTY efficiency is improved by shifting the bias deeper into class B. The heavy duty power supply and RF components, co mbined with a f orced air system utilizing chimneys, provide long service life for expensive components. The AL-1200 is shipped factory wired for 240 volt, 50/60 Hz power mains.

PLEASE READ THIS MANUAL BEFORE OPERATING THIS EQUIPMENT!

116 Willow Rd.

Starkville

MS 39759

UNPACKING INSTRUCTIONS

1. Carefully remove t he amplifier, tra nsformer, and t ube from their shi pping carto ns. Inspect each item for visible damage. If any damage occurred during shipment,

the transportation company immedi at e ly.

notif

2. Save all packi ng materials i n case you n eed to return your AL-1200(X) for factory service. The cartons have been designed to give maximum protection for this amplifier. Any units returned without proper packing may be damaged and shipping claims cannot be made. C ontact the factor y bef ore retur ning an y units .

3. Remove the scr ews that hold the cover to the amplifier. Slide the cover back and remove it from the amplifier. Remove the package that is in the area where the transformer will be mounted. This package contains the chimney for the 3CX1200A7. There is also a small package that contains the fuse s, fuse caps and the remainder of t he ch ass i s scr e ws .

4. Please read the GENERAL INFORMATION and SPECIFICATIONS sections before attempting to install the transformer and tube. Go to the INSTALLATION section on page 4 to begin installin g t he tra nsf or me r and tube.

5. This amplifier must always be disconnected from the power mains before removing the cover. S ee the precau tion on p age 10. Please rea d the e ntire manu al to become familiar with the o

eration of t he AL -12 00(X) amplifier.

1. Inexpensive tubes: the AL-1200 uses a single rugged

pag

2. Fast warm-up time: the 3CX1200A7 requires only a few seconds of warm-u

time.

3. SSB/CW switch: the bias voltage is switched to provide the best linearity on SSB or the lowest dissipation on CW operation.

6. Two Illuminated Panel Meters: the AL-1200 has two illuminated panel meters. . The Grid Current meter provides a continuous reading of grid current and indicates proper operation of the amplifier. The other meter reads Plate Voltage (HV), Plate Current (IP), Peak RF Watts (PO) and ALC.

7. Operate/Standby Switch: filament and plate voltages are maintained while allowing the amplifier to be bypassed for "barefoot" operation.

4. ALC Indicator: the drive level is detected to provide a control voltage for the exciter. ALC prevents overdriving of the linear and reduces distortion from excessive drive

ower.

5. Vernier Plate and Load Adjustments: both tuning con-

trols have vernier 6:1 reduction drives for smooth tuning.

Input

Circuit type: Pi-network, slug tuned coils maximum VSWR at resonance: 1.2:1 minimum 2:1 VSWR bandwidth: 20% maximum drive power permissible: 130 watts typical drive for full power output: 100 watts

Output circuit type: Pi-L, Pi

hour continuous carrier: 1500 watts (Below 18MHz) 30 second continuous carrier: 1800 watts plus in

hour PEP two-tone test: 1800 watts

8.12 Volt Auxiliary Jack: 12 volts at 100 mA is provided for accessories such as the ATR-15 Antenna tuner.

9. XMT Indicator LED: provides a front panel indication of proper amplifier keying by the exciter during operation.

Caution: This amplifier must be disconnected from the power mains before removing the cover. See the warning

e 10.

Metering: multimeter: plate current, plate voltage, drive/ALC, power output (PEP watts). Grid: grid current

ALC: ne Efficienc Efficienc MARS/WARC: yes, bandswitch set to nearest amateur

Keying: requires relay closure or sinking to ground of

ative going, 0-20V, adjustable, phono jack

CW: 65% typical SSB (envelope crest): 62% typical

band

ositive (+) 12 VDC at 100 mA, phono jack

Power Supply

circuit type: full wave bridge, capacitor input no load voltage: 3600V

full load voltage. 3300V full load current: .8 amp regulation: 10% or better transformer: 32 lbs., hypersil capacitors: 26 mfd total, computer grade maximum draw at rated output: 13 amps at 240V AC, 50/60 Hz

Tube type: (1) 3CX1200A7 continuous dissipation: 1200 watts warm-up time: 10 seconds

Line Connector: NEMA 6-15P 240V style

" Weight: 77 lbs. Frequency Coverage: 1.8 through 21 MHz amateur bands

Third Order IMD at Rated Output: -34 dB at 1500

output

specifications ar e subj ect to c hang e wit hout notice or obli gatio n.

SAFETY INTERLOCK

quip

ply

(

GENERAL INFORMATION

PLATE SUPPLY

While the Amplifier's top cover is in place, the interlock switch closes to allow AC line voltage to reach the power transformer. When the top cover is removed, the interlock opens and disconnects the l ine vo lt age . T his do e s no t d i scha rge t he b ank o f power supply filter capacitors. Be sure to allow the filter capacitors to discharge before you touch anything inside the Amplifier. You can select the High Voltage function of the Multimeter to check the high voltage potential. Never attempt to defeat the safety interlock.

of this amplifier with the unit plugged into the power line.

WARNING- Never remove the cover

DRIVING POWER

This Amplifier is designed to operate at full ratings when it is driven by an exciter that has approximately 100 watts of RF output. You can use an exciter that has lower output power, but the Amplifier's output will be less. If you use an exciter that delivers more than 100 watts, carefully adjust the driving power to avoid "over drive" a nd the crea tion of spur ious si gnals, whi ch create needless interference to other operators. We highly recommend that you use a monitor scope fo r continuous output monitoring. The display on an oscilloscope is the best way of determining the amplitude of the voice peaks which, if excessive, can cause "flat topping" and splatter.

IMPORTANT: In no case should you advance the power output control of your exciter beyond the point where the Amplifier's Power Output indication ceases to increase. If you turn the control past this point, nonlinear operation may occur.

The plate supply has a full wave bridge rectifier and a 1.8 KVA CCS rated tape wound hypersil transformer. Filtering is accomplished by a bank of high quality capacitors totaling 26 mfd (additional capacitance will not improve supply performance). The Plate Supply will not be harmed by normal continuous amateur operation at 1500 watt levels. Power is applied thro ugh RLY2 when the 1 2V DC lo w voltage supp ly is activated. A 10 ohm resistor limits the line current during the filter capacitor charge time to lower the stress on components. When the primary voltage approaches the full line value, RLY3 shorts the 10 ohm resistor and applies the full line voltage to the plate transformer. The 10 ohm resistor acts as a fuse during start-up if the high voltage supply has a short.

EXPORT MODIFICATIONS

A simple modification will allow operation on frequencies above 15 meters. Instructions for this modification are available by sending a written request for "Export Modification Instructions" along with a copy of a valid amateur license. There is no charge for this information. Export models are shipped with this modification and have an "X" following the serial number. Standard frequency coverages are indicated in the chart following the tuning instructions on page 6.

TECHNICAL ASSISTANCE

Technical assistance is available during our normal business hours on weekdays. The following information is required to assist

ou with operational problems:

FILAMENT SUPPLY

The filament circuit of this amplifier satisfies all requirements of the tube manufacturer related to tube performance and life. Inrush current is controlled by the transformer internal resistance and impedance, filament choke resistance and filament wiring resistance. To insure maximum life of the tube never replace any circuit components or wiring with substitute parts.

The low voltage tap on the filament transformer primary provides the ability to operate the blower at slower speeds for reduced noise. Normal amateur operation in CW and SSB will not cause heat damage to components on any recommended tap. It is always advisable to use the maximum speed (air flow) that the level of noise permits to extend component life. Wiring information for the blower is shown in the "Transformer Connections" instructions.

The high voltage present on the plate choke and air variable capacitors attracts dust and dirt out of the air stream. It is particularly important that the high voltage areas at the bottom of the plate choke and the insulators on the air variable capacitors be dust free. These areas should be inspected every few months if the amplifier is operated in a dusty environment. Unplug the line cord, and wait about 90 seconds until the power supply capacitors discharge. Remove the cover and connect a jumper wire from ground to the anode connection of the tubes.

2. Date of

3. An accurate descri

Meter readings at all stages of the tuning proceedure are very important along with a complete description of the other e

ment used with our product.

Written assistance is also avaiable. Due to time delays in

rocessing mail, please allow at least three weeks for a writ

ten re

NOTE: This is a safety wire that must be installed when beginning service work and removed when work is finished. Use a soft bristle brush dipped in alcohol to clean areas mentioned previously. In the event that cleaning is required at frequent intervals, place a low restriction air filter material over the air inlet holes on the left front side of the cabinet near the filter capacitors. Most hardware stores stock suitable materials that are used as replacement filters for window air conditioners.

urchase and dealer

tion of the problem

AMERITRON 116

Willow Road

Starkville, MS 39759

Tel: (662) 323-8211

Fax:

662) 323-6551

METERING

The AL-1200 has two illuminated meters. The Grid Current meter provides a continuous indication of the 3CX1200A7 grid current. This exclusive feature of Ameritron amplifiers indicates proper amplifier operation better than any other parameter. Do not exceed 300 mA on this meter during normal operation of this amplifier. The other meter reads Plate Voltage (HV), Plate Current (IP), Pe ak RF W a tts (P O) a nd ALC. These functio ns a re selected with the Multimeter Switch.

Plate Voltage (HV): Read DC Plate Voltage on the 4000 volt scale. This scale is 100 volts per division. Normal voltages are

00 volts no load, 3300 volts full load.

Peak RF Watts (PO): Read Peak RF Watts on the 2000 watt scale. This scale has 50 watt divisions below 1000 watts and

INSTALLATION

TRANSFORMER INSTALLA TION

Remove the cover of the amplifier. Remove the package that is in the plate transformer area. This is the fuse pack and chimney for the AL-1200. Remove the top 7/16" nuts from the four transformer mounting bolts inside of the amplifier. Carefully remove the transformer from its shipping carton.

NOTE: This circuit uses an emitter follower to charge a capacitor to the peak envelope voltage detected by the ALC/Power Board. Accurate peak envelope power readings are given when the amplifier is connected to a 50 ohm nonreactive load. If the amplifier is used with a mismatched load, the power meter will read higher or lower than normal by a ratio up to the value of the SWR. Potentiometer R5 on the Meter Board (5001140-1) adjusts the calibration of the power meter.

ALC: Indicates a relative drive level (average, not PEP) that can be estimated by dividing the Peak RF Watts scale by 10. NOTE: There is a neutralization tab mounted on a ceramic standoff near the 3CX1200A7. This tab increases the amplifier's efficiency on 21 and 28 MHz. DO NOT CHANGE THE P

ITION OF THIS TAB

Now slide the colored insulating boots back over the terminals. Important: The leads must be in the positions indicated by the color coded insulating boots(see Fig. 1) for 240V operation. For 220V operation, see page 5. Caution: Do not use the 220V wiring unless the line voltage is always below 220 VAC. The Standard USA voltage is 240 VAC, not 220

Place the transformer on the four

/4-20 mounting bolts. Use care because the transformer is heavy. The side with the two high voltage secondary RED leads must be adjacent to the center panel(see Fig. 1). Now place a 7/16" nut on each bolt (see Fig.

2). Snug the nuts do wn manually. Do not ti ghten with a ratchet wrench.

Remove the brass

/4" hex nuts and the top flat washer from the two brass 6-32 screws on the rectifier board (see Fig. 1). Install the RED lead ring terminals on the screws and replace the flat washers and 1/4" hex nuts. Position the wires so that the black insulated areas are at least objects. Now tighten the

/4"

from each other and any metal

hex nuts.

For 240V Operation (factory wired):

The four primary leads have colored plastic insulating boots over the quick disconnect terminals. Slide these back prior to installing the leads. Install the color coded boots as follows:(see Fig. 1)

BLUE (Brown wire) to the top relay terminal YELLOW (Black/White) to the top terminal of terminal

CLEAR (Black wire) to the second terminal of terminal block

RED (Brn/Wht-240V)(Grn-220V) to the bottom terminal of

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