This vibration is then amplified and the end result can sound like distortion and other unpleasant sounds. Tubes can have easy or hard jobs. If the tube is used to amplify a signal, then it is expected to make noise if tapped on. If it is used in other positions, such as an output buffer stage, then it may make no noise no matter how hard you tap on it. It can damage them, and you learn nothing about the tube's performance by doing so.
It goes on to say: "In radio receiver factories the valves are usually tested in the chassis in which they are to operate, the set being tuned to a signal generator with internal modulation, and the volume control set at maximum. Any microphonic sounds which quickly die away are not considered as cause for removal of the valve, but a sustained howl is so considered.
Such a valve may not be microphonic in another position in the chassis or in another model of receiver. A more basic tire will have a rating of S, a tire designed for higher speed and performance will be H or V, and the most expensive and highest performance rating being Z.
So it is with tubes. The message here is that at Upscale Audio, we test most small signal tubes one by one in circuit using our own process. We then grade and sort them based on their level of microphonics. Messages 6, You'll know when you have problematic microphony It will manefest as anything from out of control howling to a ringing that hangs over every note you play.
I once had a situation with a microphonic tube where not only did the ringing hang over the notes but also the whole amp would ping if you tapped on the faceplate or side of the cabinet. Peteyvee Premium Platinum Member. Messages 56, I dealt with this before with some power tubes that were acting like tiny microphones mixed with glass. The oddest sounds would come out of the amp even with the volume all the way down, which were more pronounced if the amp was tapped even lightly.
If not for that situation I would have thought nothing of this with the preamp tubes. Guinness Lad Senior Member. Messages 15, Get some of those rubber things, many times they kill the microphonic noise. Peteyvee said:. I think you misunderstood. I just haven't gotten around to putting them in yet, because I just got the amp last week.
I'm trying to avoid spending any more money! If that's not it, I'll try the tube dampers. I know a few guys that have had good luck with them. Messages 29, I've found there to be three different types of microphonic nastiness. First, the actual physical rattle sound of the tube. Annoying when recording, otherwise you can't hear it that much. Second, the "ringing" of a tube that is evident and not musical once you stop playing loud and your note tails off to silence.
Literally sounds like a fork striking glass really quickly - annoying. The worst is the HOWL. Since there are less stages of amplification following these stages the microphonics will be amplified less.
You can check your tubes for microphonics by performing this simple test: 1. Remove any back cover that may be on the amplifier to gain access to the tubes and any tube shields on the preamp tubes. Plug a guitar with the volume control at minimum or a dummy plug into the input of the amplifier.
Turn up all controls on the amplifier. The speaker reproduces this and sends out a high pressure sound wave. This sound wave hits the microphonic valve. The elements inside the valve rattle.
Valves are quite simple devices. They consists of little bits of metal elements suspended on fine wire stalks brought out to the pins on the valve base all surrounded by a glass envelope.
One thousandth of a millimetre change is definitely noticeable as a current change. Amplify this, and you would definitely hear it. The short answer is yes. Try the following experiment. Turn your amplifier up reasonably loud, then tap the first preamp valve with a biro etc. You will definitely hear the ping. In other words if you can hear nasty noises when playing. A particular valve will cause problems if its metal elements are just slightly more prone to vibration.
It can also be a problem if their resonant frequency of vibration is at a noticeable and annoying frequency.
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