User`s guide

The Nature Of Tubes — Why (And When) To Replace Them:

Tubes are made up of a number of fragile mechanical components that are vacuum-sealed in a

glass envelope or bubble. The tube’s longevity is based on a number of factors which include

how hard and often the amplifier is played, vibration from the speakers, road travel, repeated

set up and tear down, etc.

Any time you notice a change in your amplifier’s performance, check the tubes first.

If it’s been a while since the tubes were replaced and the sound from your amplifier lacks

punch, fades in and out, loses highs or lows or produces unusual sounds, the power tubes

probably need to be replaced. If your amplifier squeals, makes noise, loses gain, starts to

hum, lacks “sensitivity”, or feels as if it is working against you, the preamplifier tubes may

need to be replaced.

The power tubes are subjected to considerably more stress than the preamplifier tubes.

Consequently, they almost always fail/degrade first. If deteriorating power tubes aren’t

replaced they will ultimately fail. Depending on the failure mode, they may even cause severe

damage to the audio output transformer and/or other components in the amplifier. Replacing

the tubes before they fail completely has the potential to save you time, money and unwanted

trouble. Since power tubes work together in an amplifier, it is crucial that they (if there is more

than one) be replaced by a matched set. If you’re on the road a lot, we recommend that you

carry a spare matched set of replacement power tubes and their associated driver tubes.

After turning off the power and disconnecting the amplifier from the power source, carefully

check the tubes (in bright light) for cracks or white spots inside the glass or any other appar

ent damage. Then, with the power on, view the tubes in a dark room. Look for preamplifier

tubes that do not glow at all or power tubes that glow excessively red.

Whenever you replace the power tube(s):

• Always have the amplifier’s bias voltage checked by a qualified service center. Improper

bias voltage will cause degradation in performance and possibly damage the tubes and/or

the amplifier. (See “The Importance of Proper Biasing”, below for more information).

• We highly recommend that you replace the driver tube(s) as well. The driver tube deter

mines the shape and amplitude of the signal applied to the power tube(s) and has to work

almost as hard as the power tube(s).

You can check your preamplifier tubes for microphonics by turning the amplifier on, turning up

the gain and tapping lightly on each tube with the end of a pencil or a chop stick (my favorite).

You will be able to hear the tapping through your speakers, which is normal. It is not normal

for a tube to ring like a bell after it’s tapped. If it does ring then it’s microphonic and should be

replaced. Remember to use only high quality, low microphonic tubes in the preamplifier section.

Even though power tubes are rarely microphonic, you should check them anyway. The power

tubes can be checked for microphonics just like pre-amp tubes.

In the case of very high gain amps, you may be able to reduce the amount of noise generated

by simply swapping the preamp tubes around.

Important Information about Tubes and Tube Products: