Laney L50H - Manual (Page 16)

L50H
TUBE AMPLIFIER SURVIVAL TIPS
Tube amplifiers generally sound much warmer/sweeter than solid state transistor amplifiers but they also need a little more respect due to the fragile glass
tubes. The L50H uses three 12AX7 preamp tubes, and five EL34 output tubes which should give you years of trouble free service, however like all tube amps;
it is important to treat it with a certain amount of care. Use the following steps as a guide for how to take care of your amplifier:
! Use the Standby switch to allow the tubes to warm up before being connected to high voltages. This will prolong the life of the tubes.
! Take care when moving the amplifier. Tubes are fragile glass components, they can easily be damaged if thrown in and out of transit vans.
! Make sure the impedance of your cabinets matches the setting on your amplifier. Improper impedance matching will result in reduced output power
and compromised sound at best, and amplifier failure/shortened tube life at worst.
! Allow the amplifier to warm up to room temperature before switching it on: the sudden thermal shock can crack a cold glass tube enclosure, plus any
moisture is bad news around high voltage electronics.
! After playing, allow the amplifier to cool down before moving. Hot tubes are more fragile than cool ones.
! Always use good quality loudspeaker cables: instrument cables are not capable of handling the load requirements of the loudspeaker and can short out.
Replacing Tubes
A tubes life expectancy is based upon a number of factors which include operating temperature, how hard and how often it is played, vibration due to travel,
etc. Tubes should be changed in your amplifier if you notice any deterioration in your amplifiers sound or performance. Otherwise, they need not be changed
at any regular interval.
Typical problems with preamp tubes can be crackly noise, hiss, hum, and microphony. If they fail or exhibit reduced performance, preamp tubes can simply be
swapped out with no further action required.
Typical output tube problems can be blown HT fuse, sound lacking in punch, sound lacking extreme highs or low, and low level hum. The output tubes can be
replaced singly if you replace them with the exact same type AND grade as factory fitted, otherwise they should be replaced as a matched set.
To change a tube firstly switch off and unplug the amplifier from the mains supply. Wait for the tubes to cool down. Remove the rear protective grille held in
place with four screws. Preamp tubes are protected with a screen can; to remove, gently push down and twist the can anti clockwise and then pull up. The
tube can now be gently pulled out. Output tubes have a spring retainer which grips the base of the tube; push down on this with one hand, whilst gently
rocking the tube with the other to remove. Take care when inserting the new tube in to make sure all pins are correctly aligned.
The user should not attempt to service this product. Please refer all servicing to qualified service personnel.
OPERATING INSTRUCTIONS
Tube Type
V1-3 ECC83/12AX7
V4-8 EL34