AMERITRON AL-811H Manuel d'instruction - Page 4

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SAFETY INTERLOCK

The interlock switch stays closed to allow AC line voltage to

reach the power transformer as long as the AL-811H's top cover

is in place. When the top cover is removed, the interlock opens

and disconnects the input 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.

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 70 watts of RF

output. You can use an exciter that has lower output power, but

the amplifier's output may be less. If you use an exciter that

delivers more than 70 watts, carefully adjust the driving power

to avoid "over drive" and the creation of spurious signals, which

could 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 readily

available way of determining the amplitude of the voice peaks

which, if excessive, can cause "flat topping" and splatter.

IMPORTANT: Do not increase the drive power unless the

amplifier output power also increases. Grid current climbs

rapidly and the plate current meter and output power will

barely increase with excessive drive.

indicates the amplifier LOAD control needs to be advanced

to a higher number. Excessive plate current indicates the

drive power limit has been reached. Non-linear operation,

splatter, and excessive grid current will occur if the

"LOAD" setting it too low.

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's 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.

ALC CIRCUIT

The ALC circuit converts a portion of the RF drive voltage at

the exciter end of the tuned input circuit to a negative going

control voltage. This voltage should be used to limit the exciter

drive to safe drive levels for the AL-811H for exciters that

develop more than 70 watts of output power.

A capacitive divider consisting of C27 and C28 is used to reduce

the RF voltage and drive a rectifier circuit consisting of D17 and

D18. The resulting voltage is filtered by C29 and R12 and is

applied to the ALC potentiometer R14. R13 provides RF and

DC isolation for the ALC jack. The DC isolation prevents

loading of the exciter ALC input line by the potentiometer.

GENERAL INFORMATION

This condition

The ALC circuit can be adjusted by loading the AL-811H

slightly beyond the recommended maximum values with the

ALC line disconnected. The ALC line can then be connected

and the ALC control on the amplifier can be adjusted to a point

just before the drive begins to decrease.

NOTE: The primary use of the ALC function is the prevention

of excessive drive levels. This circuit will not prevent

small changes in output power from occurring on

different bands.

levels of drive power are those above 100 watts. Slight

changes may occur in maximum output power on

different frequencies with the ALC connected.

compromise in ALC adjustment may be necessary to

achieve acceptable performance on all bands.

PLATE SUPPLY

The power supply in this amplifier uses a combination plate,

filament and control transformer.

provided to allow the user to compensate for low, medium or

high power line voltage. This amplifier is normally supplied

wired for the highest power line voltage setting. Never change

this setting unless you are positive that performance is suffering

due to low filament and plate voltages. The life of components

will be shortened drastically if the high voltage exceeds 1800

volts at rest. The diagram on page 4 shows proper wiring for

each voltage.

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 either "X" or "Y" following the serial

number. Standard frequency coverage is indicated in the chart

on page 7.

TECHNICAL ASSISTANCE

Technical assistance is available during our normal business

hours on weekdays. the following information is required to

assist you with operational problems:

•

Model and Serial Number;

•

Date of purchase and dealer;

•

An accurate description of the problem;

Meter readings at all stages of the tuning procedure are very

important along with a complete description of the other

equipment used with our product.

Written assistance is also available. Due to time delays in processing

mail, please allow at least three weeks for a written reply.

AMERITRON

116 Willow Road

Starkville, MS 39759

Telephone: (662) 323-8211

Fax: (662) 323-6551

Under most conditions destructive

A buck boost winding is