Laney L20T-112 Operating Instructions Manual - page 13

•   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 themselves.  The L20T-112 uses top quality 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. 

•   Tubes are fragile glass components; they can easily be damaged if thrown in and out of vehicles,

•   Make sure the impedance; of your cabinets matches the setting on your amplifier.  Improper impedance matching will 

result in reduced output power output and compromised sound at best and amplifier failure/premature tube failure at worst.

•   Allow the amplifier; to warm up to room temperature before switching it on, The sudden thermal shock generated can 

crack the cold glass tube housing plus any moisture is bad news around high voltage electronics.

•   Allow the amplifier; to cool down after playing before moving.  Hot tubes are more susceptible to damage than cool 

ones.Use good quality loudspeaker leads, cheap leads are often not up to the job of handling the large requirements for 

loudspeakers and can often short out. 

•   Tube amplifiers; don't like running into a open circuit. 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 change in your amplifiers performance etc. They need not be changed at any regular interval.

•   Typical problems; with preamp tubes, can be a crackly noise, hiss, hum and microphony.  The preamp tubes can safely be 

changed with no other action required if they fail or reduce in performance. Typical output tube problems can be blown HT 

fuse; sound lacking in punch, sound lacks extreme highs or lows and low level hum. The Output tubes can be replaced singularly 

if you replace them with the exact same type AND grade as factory fitted otherwise they should be replaced as a set. See the 

diagram following to see how to check the tube grade fitted. Exact replacement preamp tubes and matched sets of output 

tubes are available from Laney via your dealer.

•   To change a tube; switch off the unit and unplug from the mains supply.  Wait for the tubes to cool down. Lay amplifier 

down on its front face and remove the protective grille held in place with four screws. You should now be able to access the 

underside of the amplifier chassis. Preamp tubes are protected with a screen can, to remove; gently twist the screen can anti 

clockwise and then pull up. The tube can then be gently pulled out. Take care when pushing the new tube in to make sure the 

pins are all aligned properly. Output tubes have a spring retainer which must be pulled away before the tube will come out.

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Amplifier connection  In order to avoid damage, it is advisable to establish and follow a pattern for turning on and off your 

equipment. With all system parts connected, effects processors etc. BEFORE turning on your guitar amplifier.  Many products have 

large transient surges at turn on and off which can cause damage to your speakers. By turning on your guitar amplifier LAST and 

making sure its Volume controls are set to minimum any transients from other equipment will not reach

 your loudspeakers.

TUBE AMPLIFIER SURVIVAL TIPS

L20T

-112