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GENERAL INFORMATION ABOUT TUBES
It is true that each brand of tube sounds different in a particular high resolution circuit. This is
because no two manufacturers make a tube type in quite the same way, and the central tendencies
of the performance parameters will differ slightly with each maker.
This sonic variability may at first seem a liability, but further thought will reveal that it is an
advantage. The owner of a tube amplifier can select those tubes which sound like the real thing in
his/her specific system. VAC can recommend the best tubes for your amplifier.
Normally vacuum tubes should last for 4,000 to 12,000 hours of use, or two to ten years for most
users. There are always occasional exceptions, long or short. If you have to replace a tube before,
say, 3,000 hours, just replace the single tube. If you have to replace a tube at 8,000 hours, replace
them all and keep those still functioning well as spares
VAC will be happy to test tubes for concerned customers.
Installing New Tubes:
Original Equipment Replacement tubes are available from VAC. These tubes ensure your amplifier
will meet or exceed all factory performance specifications.
Before replacing tubes, all power must be off. Mute unit, place power switch in the “off” position
and unplug power cord. Remove cover and old tubes ONLY after the unit has cooled down (In
normal use, tubes become hot enough to cause serious burns. Allow several minutes for tubes to
cool before attempting to remove or replace.) Install the new tubes fully firmly in their sockets,
taking care to observe the direction of the locating ridge in the plastic center pin of the large KT88
output tubes’ metal & phenolic base. With 9-pin miniature 12AU7 tubes, make sure that pin pattern
corresponds to holes in tube socket.
When changing KT88 tubes, turn the bias control corresponding to the new tube fully
counterclockwise. After turning the unit on and allowing it to reach normal operating temperature,
follow the normal biasing procedure.
In the event that trouble is encountered, switch power to the “off” position, check that all tubes are
correctly seated in their sockets and check all signal, speaker and power connections. If possible,
try another tube. If the problem persists, please consult your VAC dealer or contact the factory
directly.
