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Replacing the Tubes & Setting The Bias
Setting bias is one of lifes little neccessities when you own tube amps. The other is replacing tubes.
Considering how these are related we will treat both as one subject.
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 Stingray should be 4 to 5 years depending on useage. As with all
tubes, their quality degrades with age. This is due to gradually decreasing cathode emission, a natural process
found in all tubes.
How can I tell when I need to replace them? The output tubes (EL-84) should have their bias voltage
checked on a regular basis (see page 15). Any tube thats bias reads very different from the rest should be re-
adjusted, and closely monitored in the future for further large variations which would indicate it's time for
replacement.The input tube and occasionally the others can have other symtoms as well. An excessive
increase in noise level or distortion can indicate the need to replace a tube. Some tubes loosen up in their
internal supports and become microphonic. If you tap the tube lightly it may ring through the speakers. A
little is normal - a lot means "time for a new tube". A tube that has turned white inside means that air has
leaked in - or (as we joke) the vacuum has leaked out. Obviously, any tube that does not light up at all is bad,
too. Replace it. These tubes are not expensive, esoteric or hard to find. We always suggest that you own at
least a few spare tubes.
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 drawn number on the
top of the output tubes so we can supply you the optimum one.
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".
Is it difficult to replace a tube? Yes, if you have trouble replacing light bulbs. 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, 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
Stingray back for repair or adjustment, our warranty covers about everything except tubes (6 mo. only) and
abuse and we handle ground shipping back to you - usually the same week
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