Kessler Engineering TL-922 Revival (tm), Installation Manual

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36
Electronic Bias Adjustment and Checkout
This test confirms correct operation of the High Voltage Power Supply and Electronic Bias.
LETHAL
voltages will be present within the amplifier during these tests!!
ALL AMPLIFIER COVERS MUST BE IN-PLACE DURING TEST!!
.
Under normal conditions with a “healthy” set of 3-500Z tubes, the idling current should be
approximately 180-200mA when operating with the “MODE” switch in the SSB position,
whereas the idling current should be approximately 90-100mA when operating with the
amplifier “MODE” switch set to the
CW position. Idling current, also known as Zero-
Signal Anode Current (ZSAC) is the anode current that flows when the tubes are biased
On without RF drive signal. The RF exciter will not be attached to the amplifier for any
of these tests.
The 3-500Z vacuum tubes may be operated upright or upside-down. However, the tubes
may not be operated when oriented horizontally. The tests may only be performed with the
amplifier either upright or upside-down.
The stock TL-922 featured a fixed, non-adjustable cathode bias (Zener diode). The
Electronic Bias PCB includes adjustable bias. The bias is adjusted by setting a jumper to
1-of-7 possible bias settings. Moving the bias jumper closer to the front of the amplifier
will increase ZSAC, while moving the jumper in the opposite direction will decrease ZSAC.
ZSAC adjustment must NOT be attempted while the amplifier is operating or if plugged
into the AC mains.
Figure 3.28: Electronic Bias ZSAC Adjustment Jumper
1. Unplug the amplifier from the AC mains.
2. Ensure both tubes are installed and that the anode VHF suppressors are properly
connected to the tube anodes.
3. Install the amplifier top inner and outer covers.
4. Place the amplifier upside down.
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