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REPLACING TUBES
(Also refer to page 6)
How long will these tubes last? We can't say for sure. Some die prematurely and some tubes last more than
30 years. The average for the tubes in the 250's & 500's seems to be 4 to 5 years depending on usage. As with
all tubes, their quality degrades with age. This is due to decreasing cathode emission, a natural process found
in all tubes. One day that cathose will just not have any more electrons left to emit!
How can I tell when I need to replace them? Most problems relating to the output tubes will show up while
performing the bias procedure (see page 9). Tubes that cannot be adjusted within the specified range or have a
very unstable reading are candidates for replacement. If the tube's plate (the metal rectangular boxlike part
most visible from the outside) is glowing cherry red or orange, then the tube is severely overheated. Check its
bias immediately; if unable to adjust, then turn off the amplifier right away and replace the tube. The preamp
and driver tubes can become noisy (hiss) or the amplifier may exhibit audible distortion; substituting known
good tubes is the best way find the bad one. All tubes are "microphonic" to some extent- that is, they will
make ringing noises through the speakers when tapped or vibrated. Here again, substitution will detrmine
which one is excessively noisey. But don't be hammering on your tubes while they are hot or you'll just be
looking for problems. Obviously, any tube that is totally dark inside while powered up or is cold to the touch
(careful!) is defective. Most tubes have a silvery coating deposited on some area inside the glass bottle. If this
has turned white (compare to another tube), then the tube has lost vacuum (or gained air!) and is definitely bad.
Replace at once- don't turn the amp on.
Do I need to replace them all at once? No, at least not with these amps. Some tube amps do require that if
one tube has to be replaced that a complete matched set put in. All Manley amps use individual bias trims for
each output tube which allows a single tube to be replaced. Absolute best performance is achieved when the
tubes are most similar. We batch them and label each tube so that in the event of a replacement you can get
one from Manley of similar characteristics as the others in your amp. We need that hand written number on
the top of the tube (output tubes only).
Does the "sound" of the amp change as the tube ages? Yes, but not very much. It is just the tubes and they
can be replaced. It is not like big guitar amps where tubes are replaced every 6 months for reasons of "tone".
We run the tubes quite conservatively which allows a very long life and less change between old and new
tubes. This is where that 4 to 5 years of use comes from. You may notice an improvement between tubes this
old and new tubes depending on how critical you are. Keep in mind the sound of new tubes changes most in
the first weeks of use before they can be considered "broken in". At first the sound may be a little "tight" and
"direct" (like some people we know?).
Is it difficult to replace a tube? Yes, if you have trouble replacing light bulbs. Otherwise, it is super easy.
Turn off the power. Just let the amp cool a few minutes so that you don't burn your pinkies. It helps to wiggle
the tube gently rather than pulling it out straight. Even if you don't consider yourself "technical" you probably
have more technical ability than your parents and they used to fix the family TV set by taking out the tubes
and putting them on the tube tester at the local pharmacy. It is almost as easy to re-insert a tube. Just make
sure it is correctly lined up with the socket and you dont bend a pin. You can wiggle it in too. If you had a
solid state amp, it would be an unlikely repair. You would have to open it up, diagnose the bad transistors and
burnt resistors, de-solder, find replacements (good luck) re-solder, and hold your breath as you turn it on. Or
you could send it back, be without music for a few weeks, pay for service by the hour and get real upset when
it fries again. If one transistor goes the system is dead; not so with power tubes. No death, just limping. If you
need a tube or set of tubes Manley will be happy to sell you some (matched) at a good price and if you prefer
to send the unit back for repair or adjustment, get hold of our Tech Support Department by filling in the
Service Form on our website and book an appointment.
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