Henry Radio 3K Classic Mark II Operating And Maintenance Manual page 17

GRID/FILAMENT
SHORT - A failure of this nature can cause the amplifier to
show plate current even when it is not keyed.
Another indication of this
problem is negative grid current on the grid meter.
The tube must be re-
placed to solve the problem.
PLATE
SHORT
- A failure of this nature will cause the circuit breaker to
blow. Other high voltage shorts can cause the same symptom so you must iso-
late
the cause. If the shorted condition causes excessive plate current,
the cathode fuse will blow.
LOW OUTPUT - A 3CX120OA7 can offer many years of reliable service,
but
if
you
operate
the amplifier out of resonance the tubes will eventually go
soft making it impossible to drive the amplifier to full output.
SECTION 6.4 RELAY CIRCUIT PROBLEMS
RESTING
CUF'EENT WHEN AMPLIFIER IS NOT EXTERNALLY KEYED - If the relay is
keyed you will see normal tube resting current, therefore you must suspect
that the relay cable, exciter's relay, or one of the relays is malfuntion-
ing.
Isolate the problem by disconnecting the relay cable. If the problem
persists,
the cause is in the amplifier. If the problem disappears the
cause is in the exciter or cable. A problem in the amplifier would normal-
ly be caused by a short in the 12 VDC (26 VDC for 5K Classic) circuit or a
defective relay.
THE AMPLIFIER WILL NOT KEY - Siuspett first the relay cable, then check the
exciter's relay circuit.
Henry amplifiers key with 122 VDC (24 VDC for 5K)
and
some modern exciters use diode switching.
This combination sometimes
causes a
votlage drop in the relay line so that the relays will not key.
Measure the resistance across the exciter's relay contact. Any resistance
can cause a volt-tage drop. If this is the case, a more sensitive external
relay
may be required or a modification might be required to the exciter.
Another
cause could be that the relay power supply in the amplifier has
failed not
pro-viding the necessary voltage. Check the voltage at the
center pin of the relay jack. It should be between 12 and 20 VDC (20-30 VDC
for
5F'. Classic).
If there is no voltage check first the 3 AG fuses, then
the
components in the relay power supply. A last possible cause is a
defective relay.
6.5 HI GH VOLTAGE CIRCU IT PROBLEMS
The high
voltage in the amplifier can be lethal!
Always disconnect the
amplifier from its AC power source and turn off the power switch before you
work: on the equipment.
NO
PLATE CURRENT WITH EXCESSIVE GRID CURRENT - This is a sure indication
of a break in the high voltage line between the power supply and the tube.
You
MUST unplug the amplifier from the AC line and trace the circuit with
an ohmmeter to find the break.
HIGH VOLTAGE SHORT - A high voltage short will usually result in the cir-
cuit breaker turning the amplifier off. Also there will often be an arc in-
dicating the source of the short. Isolate the short by disconnecting the
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