Instruction manual

AL-800 Instruction Manual

Power is supplied through

"OFF-ON"

switch S2. A 10 ohm resistor (R27) limits the line current

during the filter capacitor charge time to lower component stress. When the filter capacitor

charging

current decreases sufficiently, RLY102 shorts the 10 ohm resistor. This applies full power line

voltage to the transformer. The 10 ohm resistor is protected from high-voltage supply shorts by a

two-ampere fast-blow fuse (F101) during start-up. If F101 or the 10 ohm resistor (R27) fails the

amplifier will not start. If F101 fails from a momentary HV to ground fault, meter protection diode

D117 may also fail. See the

Meters

section that follows for more information.

Meters

Current Meter (plate and grid):

The plate and grid current meter is located on the far left side of the front panel. This meter

indicates the plate current (Ip) on the right-hand meter scale. This scale has a small picket every

0.05 ampere, a large picket every 0.25 ampere, and indicates 1.5 amperes at full deflection.

The left-hand meter scale indicates the grid current (Ig). The small pickets on this "Ig" scale appear

every 5 mA and the larger pickets appear every 25 mA. The full scale "Ig" reading is 125 mA.

The plate and grid meters in this amplifier will normally indicate maximum grid current and

maximum RF output near the same "PLATE" tuning setting during adjustments. Maximum grid

current and minimum plate current also generally occur at or near the same "PLATE" tuning setting.

Note:

If the grid and plate meters always track (move together in exact step) as the tuning

controls are adjusted and if they show the same approximate amount of pointer

movement, diode D117 on the power supply board could be shorted.

D117 protects the overload circuit and the meters. This diode is located near the electrolytic

capacitors on outside edge of the main circuit board. D117 will usually short if there is a large high-

voltage-to-chassis current fault. The grid and plate current meters will not read correctly if this

diode fails. The overload circuit may repeatedly trip before full power is reached if D117 is shorted.

Multimeter

The multimeter is the meter on the right. It continuously reads the forward peak envelope power on

its left-hand scale (FWD). This scale is calibrated in 100 watt steps up to 2 kW.

The right-hand scale of this meter serves multiple functions, including measurement of the high

voltage (HV), reflected power (REF), SWR, ALC voltage output (ALC), and relative ALC threshold

(ALC SET). These four metering functions are selected by the

"MULTIMETER"

switch. See

Multimeter Functions

for more information.

Multimeter Functions

The multimeter will indicate the dc plate voltage of the PA tube when in the HV position. The

correct scale to use is the ACL / HV scale, which has a picket every 100 volts. Two zeros must be

added behind the numbers indicated on the meter scale (i.e. multiply by 100), so that "25"=2500