AMERITRON AL-1500 Kullanım Kılavuzu - Sayfa 4

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SAFETY INTERLOCK

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. WARNING- Never remove the cover

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

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 creation of spurious signals, which

create needless interference to other operators. We highly

recommend that you use a monitor scope for 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. 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.

The low voltage tap on the filament transformer primary pro-

vides 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.

PLATE SUPPLY

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

GENERAL INFORMATION

mal continuous amateur operation at 1500 watt levels. Power is

applied through RLY2 when the 12V DC low voltage 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 temperature before high voltage and RF drive 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 com-

parator 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 equals 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

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.