AMERITRON AL-811X - User Manual

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PLEASE READ THIS MANUAL BEFORE ATTEMPTING TO OPERATE EQUIPMENT!!

UNPACKING INSTRUCTIONS

1. Carefully lift the amplifier by the bottom cabinet edge out of the shipping carton. Place the

amplifier on a firm, level surface and carefully inspect it for shipping damage. Contact the

shipper immediately if any damage exists. Do not discard the carton or packing material.

2. Remove the twelve screws holding the cover on with a number 2 phillips screwdriver.

Carefully lift the cover off the amplifier. Save the screws to resecure the cover.

3. Locate the fuse pack with the two 12 amp fuses and fuse caps. If additional screws are

needed, they will be in the fuse pack also. NOTE: Fuses supplied are for 120/110/100V

operation. If you are rewiring the AL-811 for 240/230/220V operation, you must use 8

amp fuses. The AL-811X export model is pre-wired for 240V operation and is supplied with

8 amp fuses.

4. Remove the foam packing material (left side, front view) that secures the 811A tubes during

transit. Carefully unwrap the tubes. Do not dislodge the Aluminum shaft that is connected to

the rear input bandswitch wafer.

5. To install the tubes in the sockets be sure the large diameter pins line up with the two large

diameter holes in each socket. Do NOT rock or twist the tubes excessively during the

installation. If the tubes are already installed, check the tubes for proper seating. If

necessary, press the tubes down into their sockets with gentle force. Do not rock or twist the

tube(s) excessively. Also check that the anode caps are secure and did not come loose during

the unwrapping process.

6. The white ceramic anode connectors will have to be removed from the top metal cap of each

tube if it ever becomes necessary to remove the tubes from the amplifier. This can be a

difficult procedure because of the high clamping force of the internal springs in the anode

connector may hold it to the cap very tightly. The tube will break if direct upward or rocking

pressure is applied in an attempt to remove the connector. The safest way to remove the

ceramic connector is to lift the tube out of its socket. A twisting or spinning pulling motion

can then be applied while holding the ceramic connector firmly until the tube and connector

are separated. Repeat the procedure for the other tubes.

7. Install the cover with the vent holes to the left (near the tubes) by installing the back screws

first. Install all the screws loosely and tighten them only after all the screws are in place.

8. Install the fuses and fuse caps on the back of the unit. Read the manual to become familiar

with the operation of the AL-811 amplifier.

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The AL-811 is a grounded grid linear amplifier designed by Ameritron, utilizing low-cost 811A power triodes for operation in class AB2, suitable for SSB and CW modes.

Function Description

The amplifier boosts RF signals from an exciter to higher power levels for transmission. It incorporates a safety interlock to prevent operation with the cover removed, an operate/standby switch to bypass the amplifier for "barefoot" operation, and an XMT indicator LED for visual confirmation of proper keying. An ALC (Automatic Level Control) circuit is included to prevent overdriving the amplifier and minimize distortion by providing a negative control voltage to the exciter.

Important Technical Specifications

Frequency Coverage:
- Domestic model (AL-811): 160, 80, 40, 30, 20, 17, and 15 meter bands.
- Export model (AL-811X): 160, 80, 40, 30, 20, 17, 12, and 10 meter bands.
Input:
- Circuit type: Pi-Network, slug-tuned coils.
- Maximum VSWR at resonance: 1.3:1.
- Minimum 2:1 VSWR bandwidth: 15%.
- Maximum drive power permissible: 100 watts.
- Typical drive for rated output: 75 watts.
Output:
- Circuit type: Pi-Network.
- 1/2 hour carrier: 400 watts.
- 30 second carrier: 550 watts.
- 1/2 hour PEP two tone: 600 watts.
- 30 seconds PEP two tone: 600 watts.
- Efficiency: typically 65%.
Power Supply:
- Circuit type: full wave bridge.
- Full load current: 550mA.
- Regulation: 12%.
- Maximum draw at rated output: 8A.
Metering:
- Multimeter: reads HV (High Voltage) and plate current (Ip).
- Grid meter: reads PA (Power Amplifier) grid current.
Connectors:
- Relay: Keys amplifier when grounded. Sources +12 VDC open circuit and supplies 100mA when grounded. A built-in pulse canceling diode protects the exciter.
- RF input: SO-239, 50 ohm input.
- RF output: SO-239, 50 ohms needed with full power, will load into any SWR below 3:1 at reduced power output.
- Power: NEMA 15-15P 120V grounded style.
Physical:
- Dimensions: 16" D x 13¾" W x 8".
- Weight: 30 lbs.
Tubes: Uses 811A power triodes.

Usage Features

Fast Warm-Up Time: The 811A tubes require approximately 3 seconds to warm up.
Long Tube Life: The 811A tubes are designed for rugged, reliable operation, even on RTTY and SSTV modes.
Tuned Input: A Pi-Network tuned input circuit matches the 811A tubes to 50 ohm exciters.
Two Illuminated Panel Meters: The amplifier features two illuminated panel meters. The Grid Current meter provides a continuous reading of the 811A grid current, indicating proper loading. The other meter switches between High Voltage (HV) and Plate Current (Ip).
Safety Interlock: This feature removes AC power from the unit when the cover is removed, preventing accidental contact with high voltages. Users are warned never to defeat this switch and to allow filter capacitors to discharge before touching internal components.
Operate/Standby Switch: Allows the amplifier to be removed from the RF line while maintaining filament and plate voltages for "barefoot" operation.
XMT Indicator LED: A front panel LED indicates proper amplifier keying by the exciter during operation.
ALC Voltage: The ALC circuit generates a negative control voltage for the exciter, preventing overdriving and reducing distortion. It should be adjusted to limit exciter drive to safe levels, especially for exciters delivering more than 70 watts.
Power Connections: The AL-811 is supplied with a NEMA 5-15P plug for 120V operation. For 240V operation, 8 amp fuses are required instead of the standard 12 amp fuses for 120V. The AL-811X export model is pre-wired for 240V and supplied with 8 amp fuses. The manual provides a transformer connection chart for various line voltages (100V, 110V, 120V, 220V, 230V, 240V).
Ventilation: The system is designed to maintain safe 811A tube temperatures at 400 watts output with 100% duty cycle. Users are advised not to block ventilation holes, restrict airflow, or add external fans that exceed the internal fan's CFM by a factor of 2:1.
Grounding: A good earth or water pipe ground should be connected to the ground post on the rear panel using the heaviest and shortest possible connection. It is recommended to ground all equipment to a single point.
CW Tune-Up Procedure: A detailed step-by-step procedure is provided for tuning the amplifier, including setting switches, checking voltages, applying drive, and adjusting PLATE and LOAD controls for maximum output power while monitoring grid and plate currents. Users are cautioned not to exceed 100 watts of drive or 200mA of grid current during tune-up and to limit plate current to 700mA.
SSB Operation: Meter readings on SSB are typically 20-50% of CW carrier readings due to speech waveform characteristics. A peak reading wattmeter or monitor scope is recommended for accurate output measurement.
SSTV, FM, RTTY, PACKET, AMTOR Operation: For these modes, plate current should be limited to 400mA maximum, and grid current to 120mA. The amplifier should be tuned for peak output power with reduced drive to maintain these limits.
QSK Operation: The internal open-frame relay has a switching time of approximately 15ms, which is not suitable for high-speed QSK CW. Ameritron offers an optional high-speed PIN diode switch (QSK-5) for operators requiring faster switching (1ms).

Maintenance Features

Unpacking Instructions: Detailed steps for safely unpacking, inspecting for damage, removing the cover, locating fuses, removing foam packing, and installing tubes. Users are advised to align large diameter pins with holes in the sockets and avoid rocking or twisting tubes. Instructions for removing ceramic anode connectors are also provided.
Periodic Maintenance: The manual emphasizes the importance of keeping high voltage areas (plate choke, air variable capacitors, insulators) dust-free. These areas should be inspected every few months, especially in dusty environments. Before maintenance, the unit must be unplugged, and filter capacitors allowed to discharge for at least 90 seconds. A jumper wire from ground to the anode connection of the tubes is recommended as a safety measure during service work. A soft bristle brush dipped in alcohol can be used for cleaning.
Troubleshooting: Common issues like high VSWR, backward grid meter readings, high grid current with low plate current, and blown fuses are addressed with potential causes and solutions. For example, high VSWR might indicate an issue with the tuner, feed line, or antenna, while blown fuses could be due to shorted tubes, HV capacitors, or rectifying diodes.
Tuning Chart Log: A blank chart is provided for users to record their actual LOAD and PLATE settings for various bands (160 CW, 160 SSB, 80 CW, 75 SSB, 40 CW, 40 SSB, 30 CW, 20 CW, 20 SSB, 17 CW, 17 SSB, 15 CW, 15 SSB). This helps in quickly changing bands and adapting to antenna changes.

Safety Warning:

Users are explicitly warned not to operate the amplifier with the cover removed due to fatal high voltages inside. The amplifier must always be disconnected from the power mains, and filter capacitors allowed to discharge before removing the cover.