Ameritron AL-1500 Service manual

AMERITRON AL-1500

UCTIO

FULL POWER LINEAR AMPLIFIER

INSTR

The Ameritron AL-1500 is a 1500 watt output linear amplifier that operates from 160 through 15 meters. The Ameritron AL-1500X is the export model and covers 160 through 10 meters. The AL-1500J is the export model for Japan and covers 160 through 10 meters. The AL-1500 uses a single 3CX1500A7/8877 tube in a class AB2 grounded grid circuit. CW, FM and RTTY efficiency is improved by shifting the bias dee per into class B. The heavy duty power supply and RF components, combined with a forced air system utilizing a chimney, provide long service life for expensive components. The AL-1500 is shipped factory wired for 240 volt, 50/60 Hz power mains.

N MANUAL

PLEASE READ THIS MANUAL BEFORE OPE RATING THIS EQUIPMENT!

116 Willow Rd.

Starkville, MS 39759

UNPACKING INSTRUCTIONS

anode connector.

1. Carefully remove the amplifier, transformer, and tube from their shipping cartons. Inspect each item for visible damage. If any damage occurred during shipment,

the transportation company immediately.

notif

2. Save all packing materials in case you need to return your AL-1500(X/J) for factory service. The cartons have been designed to give maximum protection for this amplifier. An y units returned without proper pa cking may be damaged and shippi ng claims cann ot be mad e . C ontact the factor y b efore returnin g a ny u nit s .

3. Remove the screws that hold the cover to the amplifier. Slide the cover back and remove it from the amplifier. There is a small bag that contains the fuses, fuse caps and the remainder of the chassis screws wrapped in the packing material around the

4. Please read the GENERAL INFORMATION and SPECIFICATIONS sections before attempting to install the transformer and tube. Please note that the tube chimney comes factory installed around the tube socket. Go to the INSTALLATION section on page 4 to begin installing the transformer and tube.

5. This amplifier must always be disconnected from the power mains before removing the cover. See the precaution on page 10. Please read the entire manual to become familiar with the o

NOTE: The AL-1500J is the Japanese export version of the AL-1500 amplifier. The AL-1500J utilizes a special power transformer for use with 200V AC, 50 Hz. The AL-1500J will perform to specifications with the special transformer installed and will cover 24 and 28 MHz.

eration of the AL-1500(X/J) amplifier.

FEATURE

(PO)

accessories such as the

yes,

1. High performance tube: the AL-1500 uses a single rugged

2. High power gain: the 3CX1500A7/8877 features high power gain. As little as 65 watts of drive power will pr vide 1500 watts of out

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

eration.

ut power.

proper operation of the amplifier. The other meter reads Plate Voltage (HV), Plate Current (IP), Peak RF

Watts

and ALC.

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

eration.

8.12 Volt Auxiliary Jack: 12 volts at 100 mA is provided for

ATR-15 Antenna tuner

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 dri ve

ower.

5. Vernier Plate and Load Adjustments: both tuning controls have vernier 6:1 reduction drives for smooth tuning.

6. Two Illuminated Panel Meters: the AL-1500 has two illuminated panel meters. The Grid Current meter provides a continuous readin

of grid current and indicates

Input:

Circuit type: Pi-network, slug tuned coils Maximum VSWR at resonance: center frequency Maximum drive power permissable: 100

Output: Circuit type: Pi-L, Pi

hour continuous carrier: 1500 watts 30 second continuous carrier: 2500 watts 1/2 hour PEP two-tone test: 2500 watts plus 30 second PEP two-tone test: 250 0 watts

Power Supply: Circuit type: full wave bridge, capacitor input No load voltage: 3600 V Full load voltage: 3300 V Full load current: 1 amp

Regulation: 10% typical Transformer: 34 lbs., hypersil Capacitors: 26 mfd total, computer grade Maximum draw at rated output: 15 amps at 240V AC 50/60 Hz

1.3:1

Minimum 2:1 VSWR bandwidth: 20% of

lus

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

10. Grid Overload Circuit: this amplifier has a circuit that

protects the tube from excessive grid current. If 175 mA of peak grid current is reached the "OPR" LED will no longer light and the amplifier will go into a bypass condition. This overload condition can be reset by momentarily putting the STBY/OPR switch in the STBY position.

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

10.

Metering: Multimeter: Plate current, plate voltage, drive/ALC, power output (PEP watts)

ALC: Negative going, 0-20V, adjustable, phono jack Efficiency CW: 65% typical

Efficiency SSB (envelope crest): 62% MARS/WARC: Keying: Requires relay closure or sinking to ground of

set to nearest highest amateur band

t 12V

DC at 100 mA, phono jack

RF Connectors: S0239

Line Connector: NEMA 6-15P

240V style

Weight: 77 lbs.

Tube: Type:(1) 3CX1500A7/8877 Continuous dissipation: 1500 Watts Warm-up time: 180 seconds

Frequency Coverage: (AL-1500)-1.8, 3.5, 7, 14, 18 and 21

MHz. User modified models cover 24 and 28 MHz. (AL1500X/J) Export models-1.8, 3.5,7, 14, 18, 21, 24 and 28 MHz.

Third Order IMD at Rated Out

ut: -36 dB

GENERAL INFORMATION

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 line voltage. This does not discharge the bank of 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 65 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" and the cre ation of sp urious signal s, which create needless interference to other operators. We highly recommend that you use a monitor sco pe for continuous ou tput 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. This amplifier has a circuit that protects the tube from excessive grid current. If 175 mA of peak grid current is reached, the "OPR" LED will no longer light and the amplifier will go into a bypass condition. This overload condition can be reset by momentarily putting the STBY/OPR switch in the STBY position.

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.

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.

mal continuous amateur operation at 1500 watt levels. Power is applied thro ugh RLY2 when the 12 V DC low volta ge supply 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 approahces 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.

TIMER OVERLOAD BOARD

The AL-1500 has a circuit board mounted on the front panel side of the filter capacitor board that provides time delay to insure the cathode of the 3CX1500A7/8877 has reached proper operating tempe rature befor e high voltage and RF d rive power can be applied. This board also samples the peak grid current and removes drive if the grid current is excessive. The timer portion if this circuit board uses IC1A as a comparator to drive the complimentary darlington 01 and 02. When twelve (12) volts is first applied to terminal "Y" diode D3 provides a regulated 5.1 volt reference. Divider R8 and R7 reduces the reference voltage to 3.7 volts. C9 charges from current supplied by R9. After approximately three minutes, the comparator output (pin 1) goes high. Q3's collector goes low and turns on Q2 and Q1. If the 12 volt supp!y is momentarily interrupted diode D1 discharges C9 through R6, R7, and R8. Any interruption of more than a few seconds requires a complete timing cycle to begin again.

The grid overload circuit compares the voltage developed across the grid shunt (. 3V equal s 200mA) to the .256V reference provided by R5 and R11. This sets the grid trip at 175 mA. Pin 7 of IC 18 will go high and turn 04 on if the grid current reaches 175 mA. This will cause RLY 1 to latch on and remove the 12 volts from the antenna transfer relay in the amplifier. The circuit is reset by putting the amplifier on standby momentarily. This removes the voltage that holds RLY 1 locked on. NOTE: The grid overload circuit will respond much faster than the grid meter can indicate grid current. if the overload continuously trips, the likely cause is excessive peak grid current. This is caused by the loading control being set too low (counter-clockwise) for the peak drive power applied to the amplifier.

EXPORT MODIFICATIONS

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 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 nor

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 or J" following the serial number. Standard frequency coverages are indicated in the chart following the tuning instructions on page 10.

METERING FUNCTIONS

s scale is

(

The AL-1500 has two illuminated meters. The Grid Current meter provides a continuous indication of the 3CX1500/8877 grid current. This exclusive feature of Ameritron amplifiers indicates proper amplifier operation better than any other parameter. Do not exceed 75 mA on this meter during normal operation of this amplifier. The other meter reads Plate Voltage (HV), Plate Current (IP), Peak RF Watts (PO) and ALC. These functions are 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 3600 volts no load, 3300 volts full load.

Plate Current (Ip): Read DC Plate Current on the 1000 mA scale. Thi

25 mA per division

Peak RF Watts (PO): Read Peak RF Watts on the 2000 watt scale. This scale has 50 watt divisions below 1000 watts and 100 watt divisions above 1000 watts.

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 (50-01140-1) 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.

TECHNICAL ASSISTANCE

Technical assistance is available during our normal business hours on weekdays. The following information is required to assist you with operational problems:

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 equipment used with our product.

Written assistance is also available. Due to time dela ys in

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

ten reply.

urchase and dealer

tion of the problem

AMERITRON 116

Willow Road

Starkville, MS 39759

Tel: (662) 323-8211

Fax:

662) 323-6551

PERIODIC MAINTENANCE

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 capacito rs discharge. Check the HV scale for zero voltage before removing the cover. Remove the cover. You must first connect a jumper

wire from ground or chassis to the anode connection

the tubes.

INSTALLATION

TRANSFORMER INSTALLATION

Remove the cover of the amplifier. Remove the small package that is wrapped around the anode connector. This is the fuse pack and contains the fuses, fuse caps and the remainder of the chassis screws. Remove the top 7/16" nuts from the four transformer mounting bolts inside of the amplifier. Carefully remove the transformer from its shipping carton.

Place the transformer on the four because the transformer is heavy. The side with the two high voltage secondary RED leads must be adjacent to

/4-20 mounting bolts. Use care

NOTE: This is a safety wire that must be installed when beginning service work. After service is complete, reverse the procedure to remove the safety wire. Remove the wire from the anode connection first and then from ground. 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.

the center panel(see Fig. 1). Now place a 7/16" nut on each bolt (see Fig. 2). Snug the nuts down manually. Do not tighten with a ratchet wrench.

Remove the brass

/4"

hex nuts and the top flat washer from the two 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 insulated areas are at least ob

ects. Now tighten the

/4"

hex nuts. Position the wires so that the black

/4"

from each other and any metal

hex nuts.

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