AMERITRON AL-80B, Инструкция по эксплуатации

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AL-80B Instruction Manual
5
Power Supply
Filament Supply
The filament circuit of this amplifier satisfies all requirements of the tube manufacturer related to
tube performance and life. The filament voltage and inrush current are controlled by the power
transformer's internal resistance and impedance, filament choke resistance, filament wiring
resistance, and the step-start circuit. NEVER replace any circuit components or wiring with
substitute parts. This precaution will insure maximum life for the tube.
Plate (HV) Supply
The plate supply uses a full wave doubler circuit with 200 amp surge rated diodes and a heavy duty
26 pound grain oriented transformer. Filtering is accomplished by a bank of high quality computer
grade capacitors totaling 26 mFd. Large 50k ohm, 7 watt bleeders are used for safety and superior
voltage equalization. The transformer allows user selection of fourteen different line voltages (see
the "Transformer Connections" section on page 12 for details).
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 2A slow-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 "Metering Functions" 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 25
mA, a large picket every 75 mA, and indicates 750 mA at full deflection.
The left-hand meter scale indicates the grid current (Ig). The small pickets on this "Ig" scale appear
every 10 mA and the larger pickets appear every 50 mA. The full scale "Ig" reading is 250 mA.
The plate and grid meters in this amplifier normally indicate maximum grid current and maximum
RF output at or near the same "PLATE" tuning setting. Maximum grid current and minimum plate
current also generally occur at 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 (if used) 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. If D117 is shorted the overload circuit (if used) may repeatedly trip and the grid
current may appear excessively high before full power is reached.