Лампы меня всегда пора. Это как сигарета - одна затяжка и это уже бычок. Если есть деньги то желательно менять через два три концерта (репитиции).
Replace the tubes when:
* It is broken, and/or there is a white spot on the top or sides of the tube. The "getter" coating found in these areas is normally black or silver colored. By the way, a chocolate brown getter simply means the tube has had a lot of use. It still may test good.
* It tests weak or shorted. Always use a "mutual conductance" type tube tester for testing. Cheap emission type testers with "good/bad" meters are almost useless. Always replace a shorted tube, even if it tests good. Shorts can damage expensive amplifier parts.
* You cannot afford to lose your amplifier during a performance. Professional players minimize downtime by replacing the power tubes every few concerts, and by using several amplifiers. The price of tubes is cheap compared to the embarrassment of losing an amplifier on stage!
* The amplifier starts to sound bad, especially when first turned on.
So how do you know when tubes are starting to fail? Consider the following:
Small-signal (preamp) tubes (12AX7, 12AU7, 12AT7, 5879, etc.): You may hear a crackle for a short time after the amplifier is turned on. Then it quiets down. Or the amplifier may "howl" at high volumes, or buzz on certain notes all the time. These problems get worse, and eventually you will be replacing one or more tubes.
Power tubes (6L6, 6V6, 7027, 6CA7/EL-34, 6550/KT-88, etc.): Upon turning on the amplifier, the sound may be hazy, with flabby bass and scratchy treble. After about five minutes of this, the sound starts to clear up, and the amplifier sounds fine from then on. As the tubes get weaker, it will take longer for the sound to clear up. Eventually you have to replace the power tubes as a set. For reliability we strongly encourage you to replace all power tubes at a time, even if one or more tubes are still good. Also, make sure your technician set the bias correctly after they are installed. You may keep any good tubes as spares for emergencies, though.
Rectifier tubes (5AR4, 5Y3, 5U4, etc.) are not in the signal path and do not affect the sound as much. However, if you notice more distortion than normal when playing at high volumes, the tube is probably half-dead and should be replaced.
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