Specifications

Alpha 9500 HF Linear Amplifier Operating Manual Alpha Radio Products
Amplifier Components Product Release 1
DOCNUMBER 9500
Document Issue 1, Revision 7
Page 2–8 June 2009
22
2
If you install your amplifier in a location where the line voltage is not
steady, you can force the tap selection via the serial or USB port. For
information on how to force tap selection, contact ALPHA technical
support.
Also on the mains board is a step-start circuit. This circuit consists of a
relay and a resistor, which are time-sequenced to limit the inrush current
into the amplifier when it is first turned on.
HV Board
The main high voltage for the amplifier is created on the HV board using
a full-wave bridge rectifier and a bank of capacitors. This power supply
has two 10-ohm resistors, one in the positive (B+) lead and one in the
negative return to the tube cathode. This combination of resistors limits
the surge current in the case of a B+ arc. The voltage across the resistor in
the negative return monitors tube plate current in the control board. This
voltage also generates the hard-fault condition.
When the power-supply current exceeds about 2.5 amps, a latching relay
opens the coil circuit of the mains tap relays on the mains board, causing
the amplifier to go to the power-off state. This hard-fault circuit operates
independently of microprocessor control.
All power-supply filter capacitors on this board have bleeder resistors that
discharge the capacitors in less than 60 seconds. If you must work on this
board, confirm the discharged condition with a voltmeter, due to the
remote possibility of bleeder resistor failure.
2.10 Tube and Tube Deck
The ALPHA 9500 uses a single 8877 triode tube. The tube operates well
within its published ratings. It is operated in Class AB1, with a plate
voltage of 3300 V (nominal, full output, key down) and a cathode voltage
of 9.4 V.
The tube deck is a mechanical assembly that houses the tube socket and
the cathode (or input match) printed circuit board (PCB).
A temperature sensor mounted on the cathode PCB measures the
temperature of the air immediately below the tube socket. This
temperature measurement is used by the master controller as part of the
fault-detection software.