Henry RF Amplifier Troubleshooting Tips

Henry RF Amplifier Troubleshooting Tips
EXCESSIVE PLATE CURRENT “ This symptom is usually caused by a
defective 3-500Z tube, and the only cure is to replace the tube.
The amplifier can not be operated with just one tube because the
Cubo Es are in series - - 10 volts at 15 amps (5 volts per
tube).
Excessive resting plate current can often be caused by a failure
of Dl, the bias diode. Replace the diode to solve the problem.
GRID/FILAMENT SHORT - A failure of this nature in the 3-500Z 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 meter. Again the tube must be replaced to correct
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 isolate the cause. If the shorted condition
causes excesssive plate current, the cathode fuse will blow.
LOW OUTPUT - A 3-500Z 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.
RESTING CURRENT WHEN AMPLIFIER NOT 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 malfunctioning. 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 normally be caused by
a short in the 12 VDC circuit or a defective relay.
THE AMPLIFIER WILL NOT KEY - Suspect first the relay cable, then
check the exciter's relay circuit. Henry amplifiers key with 12
VDC and some modern exciters use diode switching. This
combination sometimes causes a voltage 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 voltage
drop. If thie is the case, a higher voltage external relay may
be required or a modification might be required to the exciter.
Another cause could be the relay power supply is not providing
the 12 VDC. .Check the voltage at the center pin of the relay
jack, it should be between 12 and 20 VDC. If there is not
voltage check first the 3 AG fuses, then the components in the
relay power supply. A last cause of the problem could be a
defective relay.
The high voltage in your amplifier can be -lethald Always
disconnect the amplifier from its AC power source and ‘turn off
the power switch before repairing it.
NO PLATE CURRENT WITH HIGH 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 and trace the
circuit with an ohm meter to find the break.
HIGH VOLTAGE SHORT - A high voltage short will usually result in
the circuit breaker turning the amplifier off. Also there will
often be an arc indicating the source of the short. Isolate the
£ehort by disconnecting the high voltage lead between the RF
section and the power supply. If the short persists, the problem
is in the power supply. If it disappears the problem is in the
RF section. If the short is in the RF section, remove the top
cover and search for visible evidence. Then use an ohm meter to
trace the circuit from the high voltage input socket to the
blocking capacitors, including the tubes. If the problem exists
in the power supply you will again have to use an ohm meter to
trace the circuit to find the location of the short. Bad
rectifier diodes can often be isolated by measuring their
resistance. Good diodes have infinite reverse resistance and bad
diodes have a very low reverse resistance. Some of the
components such as the transformer, choke, and diodes may only
short when the high voltage is applied. To isolate the problem
here you will have to progressively disconnect components from
the circuit until the short no longer happens. Start with the
filter capacitor, progress to the filter choke, then the diodes,
then the power transformer. Remember, a short in the RF section
may require replacement of the 1.5 amp cathode fuse.
LOW HIGH VOLTAGE - This problem is usually an indication of low
AC line voltage.
EXCESSIVE HIGH VOLTAGE - This is a problem that can be seen when
the filter choke is out of resonance. A resonanted filter choke
is used because of the superb linearity and voltage regulation
provided. However, the choke must be resonated by a capacitor.
If that capacitor fails, or changes value the choke is no longer
resonated and the voltage regulation becomes poor. The result
will be excessive high voltage when _the amplifie is t
transmitting and excessive voltage drop during Pransmit. This
means the power supply is set up for 60 Hz operation but is
operating at 50 Hz. Additional capacitance is required to
resonate the choke at 50 Hz.
NO HIGH VOLTAGE METER READING - The most likely cause is a
failure of the 8 AG, 1-1/2 amp meter protection fuse. Another
cause is a failure or value change in the high voltage multiplier
resistors in the power supply. |
The blower is one of the most susceptible parts to transportation
damage, Henry amplifiers use squirrel cage blowers because of
their exceptional air blowing capability in a small size. But
the blower assembly can be easily damaged if the amplifier is
dropped during shipment. Therefore when the amplifier is
installed make certain that a strong flow of air is coming out
the top of the amplifier when it is turned on. Other.indications
of blower damage can be a resonance in the amplifier cabinet
caused by an unbalanced fan, or an unequal flow of air between
the two tubes.
If the blower is not operating, check the 3 AG fuses. A good
indication that they are blown is that the pilot lights are not
working.
The first thing to check if there is low output is the check for
adequate drive from the exciter. Eimac 3-500Z tubes will give
approximately 10 dB of gain (about 10 times amplification). Some
modern solid state exciters have power drop off on some bands so
therefore the output from the amplifier will put out
correspondingly less power. Since the amplifier 1s a superbly
linear device its output varies directly with its input.
The next thing to check is input and output cabling. An
intermittent or shorted drive cable can cause low input or no
input to the amplifier. This will usually show up by operating
the exciter through the amplifier (in standby) and measuring the
power. Low drive power can be seen as low grid current during
transmit. Also check the output cables. Shorted coax is not
uncommon and a poor job of installing coax connectors can cause
severe output problems.
Other problems that can reduce output are low plate current,
insufficient filament voltage, low AC line voltage, or bad
tubes.
The transformers in your amplifier have taps to compensate for
unusual AC line voltage at the operating location. Normally the
transformers are wired for 220 VAC operation. If your AC line
voltage is far different from the norm then most of the operating
parameters of your amplifier will be different. To help
compensate for this difference the power transformers have taps
for 200 VAC, 220 VAC, or 240 VAC operation on their cimarys e
primaries of the transformers should be wired to the following
taps:
200 VAC 220 VAC 240 VAC
2K-D Classic....Taps 2 and 5..Taps 1 and 6.....nNn0ne..e...
2К--С1ав51С. „о о оооооо о ПОПЕ о о о ооооо о ПОЛЕ о 0000000. NONE, ....
2K-Classic X....Taps 1 and 2..Taps 1 and 3..Taps 1 and 4
AMPLIFIER WILL NOT TURN ON - The most likely cause is the circuit
breaker. Check the continuity of the circuit breaker with an ohm
meter if the amplifier will not turn on or off. Another possible
cause is the improper installation of the power plug on to the
power cable. , If the high voltage turns on, but the pilot lights,
blower, and relay supply do not come on the 3 AG ‘fuse has blown.
ALC CIRCUIT SHORTED - A defect in the ALC circuit can prevent the
tubes from being driven properly.
FILAMENT VOLTAGE FAILURE - Check the tubes when the amplifier is
first turned on to make certain that they are lighting. If they
are not check the filament connection between the power supply
and RF deck, and then the filament transformer or filament
windings of the power transformer on the 2KD-Classic and the
2K-Classic.