Small Tube Testing Options

Options We Offer

We offer the following testing options on small signal tubes like 12AX7, 6DJ8 and 5670:

• Triode Matching +$2 per tube. Pre-screened tubes are available on our site.

• Matched Pair +$2 per tube (+$4 for the pair). Pre-screened pairs are available on our site.

• Low Noise Screening +$4 per tube. We can add this to your order.

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Specifying Screening Options

• On popular tubes, we have listed pre-screened tubes and pairs. Price of screening options are already included in the price.
• If we haven't made pre-screened tubes available, you can still specify these options by leaving us a comment during checkout. Just let us know which ones you want matched, and we will adjust your order.
• You can request Low Noise Screening on tubes the same way. Tell us which ones you want screened for low-noise at checkout.

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About Vacuum Tube Noise

Microphonics

Microphonics is when tubes pick up mechanical vibration, and outputs it as electrical signal. This is just like a microphone, hence the name microphonics. This happens because electrodes in vacuum tubes can be quite sensitive to mechanical vibration.

If tubes are badly microphonic, it will start picking up its own output via sound waves from speaker. You may hear this only when certain notes are hit. Or worst case, it can go into feedback and turn your amp into a siren.

Some expensive tubes employ better construction to reduce microphonics. Still, all tubes are microphonic to some extent, and if your application calls for low microphony, it's better to have pre-screened tubes.

Noise Floor

As the name implies, there is no air inisde of Vacuum tubes. Practically speaking, there usually is trace amounts of air molecules left inside. These left over molecules can cause various noise.

Some air molecules always remain inside when a tube is manufacturerd. This is where getter comes in. Getter, the silver or dark coating inside a vacuum tube glass, work by absorbing these stray molecules.

Vacuum tubes have some inherent white noise, but some have higher noise than others. This is because of how much of the air molecules (ion particles) remain inside. These impurities can cause pop and crackle, or low frequency rumble.

As particles are absorbed into getter, the noise floor will often lower as well. Perhaps this explains why some of us feel that we hear more details after tubes have been used for a while.

On the other hand, bad noise caused by too much left-over ion particles and other contamination tends not to go away. So it's better to start with low noise tubes for best results.

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by TubeTech