Things To Bear In Mind When Replacing Tubes - Hughes & Kettner Statesman Head EL34 Manual De Instrucciones

Statesman Series
cable? If you don't get to the bottom of the problem and remedy it,
it may crop up again even after you replace the tubes.
•
Did the Mains voltage fl uctuate or spike while the amp was on? In
all-tube amps, over-voltage surges in the Mains net can certainly
cause drop-outs. Over-voltages are often caused by generators and
faulty high-current power circuits.
•
Perhaps a fuse blew even though none of the tubes is actually
defective? An old fuse, tube de-ionization or Mains voltage power
surges may have triggered the fuse.

Things to Bear in Mind When Replacing Tubes

Replacing tubes is a job best left to qualifi ed professionals!
Accordingly, the following guidelines are addressed and apply to
qualifi ed service technicians only:
•
Pull Statesman's Mains plug and allow for a discharge time of at least
two minutes before removing the chassis from the rear of the amp.
•
The upright mounted preamp and power amp tubes of all Statesman
combos are seated in a self-contained chamber that is easily
accessible from outside. And so they are optimally protected against
vibrations through the loudspeaker's vibrations.
•
After removal of the protective grid, the measuring points and
controller for setting the correct bias current and the heating
symmetry ("hum balance") are also directly accessible.
•
The illustration shows (from left to right) the aperture for the bias
trimmer, the jumpers to the measuring points, and the aperture
for the trimmer to the hum balance. The two trimmers may not be
mixed up, since otherwise there is a danger of output stage damage
through excessively high current in the tube!
Absolutely pay attention to preparations and chronological order!
1. Turn off the device
2. Exchange tubes
3. Remove all jumpers
4. In tubes with the same characteristic curve, do not change the
position of the bias trimmer. In tubes with unknown characteristic
curve, turn the bias trimmer to the right-side stop (lowest current).
5. Turn on the device
6. Measure and adjust the bias current (equivalent voltage): The
jumpers bypass a shunt resistor. When removing the jumpers, the
cathode current can be determined via the exposed pins through
a voltage measurement. The following applies in this connection:
1 mV is equivalent to 1 mA. The order of the jumpers from left
to right corresponds to the order of the appurtenant tubes from
left to right. The bias current is correctly adjusted if a voltage
between 25 and 31 mV is applied to the pins (between the upper
and lower pin of the respective jumper) with all tubes. If this
voltage range cannot be adjusted to all tubes, the divergent tubes
must be exchanged and a suitable tube must be found. For this
reason Hughes & Kettner offers selected tube sets with similar
characteristic curves.
7. Turn off the device
6
8. Put on all jumpers. Attention: Do not forget to put the jumpers on
again after successful alignment! Never operate the amp without
jumpers!
9. Turn on the device
10. Carry out hum balance Basic setting: Switch the amp to CLEAN,
turn VOLUME, TREBLE and MID to the left-side stop, and turn
BASS to the right-side stop. With the help of the trimmer, look for
a setting in which the lowest humming emerges.
11. Mount the protective grid again
4
. Sources Possible Error/
Troubleshooting
Mains connection: STATESMAN
won't power up when you switch it on.
•
It's not getting AC power. Check the Mains cord to see if it is
connected and fi rmly seated.
•
The Mains fuse is defective. Ensure it is replaced with another fuse
bearing the same rating.
•
The local Mains voltage does not match Statesman's operating
voltage
Available Voltages and How to Adapt Them
Statesman ships in two versions rated for 110/120V and 220-240V.
You will fi nd the rating indicated on the housing above the Mains
socket. Both models offer two operating voltages that are selected
using the voltage selector integrated in the Mains socket. Ensure that
the Mains voltage matches the voltage rating appearing in the voltage
selector window. This value is legible when the amp is in the standard
operating position, that is, placed right side up. The upright number
indicates the currently selected voltage, and the inverted number
indicates the alternative voltage. Check also the fuse ratings to ensure
they match the ratings indicated on the rear panel. Voltage selection
and fuse replacement may be performed by experienced service
technicians only.
Accordingly, the following notes are addressed exclusively to service
technicians:
•
Use a small fl at screwdriver to remove the voltage selector from the
Mains socket.
•
If the fuse is defective, replace it with a fuse bearing the specifi ed
rating.
•
Turn the voltage selector and insert it back into the port so that the
desired Mains voltage rating is legible and appears at the top left
(next to the "Voltage Setting" arrow).