With so much variety in the type and condition of vintage vacuum tubes, our goal is to offer as much detail and transparency as possible to help you choose the right tube for your application.
Every tube on our website is tested to determine its condition and screened for shorts and gas unless otherwise stated in the description.
Test Results
We can provide test results for tube performance at the actual operating voltages found in audio equipment (up to 500V @ 160 mA). Test results are available in engineering units for both transconductance (Gm) in mA/V (1 mA/V = 1000 uMHOs) and emission in DC milliamperes. These results are also available in "percentage of specification" readings based on manufacturer specifications published in vintage tube data books.
We are in the process standardizing the way we list test results on our website, so if you have questions about the description of a particular tube, let us know and we can offer more information.
Test Equipment
In addition to calibrated vintage tube testers, our testers include the laboratory grade Amplitrex AT1000.
The AT1000 tests transconductance (Gm), emission, shorts, and gas and heater-to-cathode leakage (where applicable) at the actual operating conditions found in audio equipment. It also has a headphone jack so any amplifying tube (including power tubes) can be checked for microphonics.
AT1000 Features Overview
The AT1000 is optimized to precisely test audiophile-grade tubes. Its features include the following:
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Tests tubes at real-world power levels, up to 500V @ 160mA
- Accuracy and Stability:
+/-1% for heater, plate, screen, and grid supplies
+/-1% for GM and emission (plate current) measurements
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Microphonics Test: Any amplifying tube, including power tubes, can be checked for microphonics
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Shorts Test: Tube is continually evaluated for shorts during the test sequence
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Gas Test: Detects effects of ionic gas current on grid circuit impedance
Matching
The AT1000 is ideal for matching plates within multi-section tubes and matching tubes to each other. Not only can we match tubes by transconductance, but tubes can further be matched by emission (plate current). And most importantly, we will match tubes at normal current and voltage levels, faithfully reproducing the actual operating conditions found in audio equipment.
Test Result Classifications
We classify each tube by its test results (see classification descriptions below). The results will be reflected in the price range for the product. Click "more info" to select the classification you need for your application. In some cases, we will also list the actual test results.
We use four classifications for vintage tubes:
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Tests as Premium New: We describe dual triode tubes as premium new if they test at or above 85% of the industry
standard value for a new tube, and both plates are matched to within 5% for Gm and 10% for plate current. Matched pairs of dual triode tubes will all have matched plates. For most higher-end tubes, we will list the actual test scores.
- Tests as New: These tubes test at or above 85% of the industry
standard value for a new tube. For most higher-end tubes, we will list
the actual test scores.
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Tests Good: These tubes test between the minimum good and 84% of the industry standard value for a new tube.
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Bargain: Occasionally, we offer tubes that work just fine, but don’t pass the minimum standard for “good” tubes. These would be in the “questionable” zone in many vintage tube testers. This is only done when the tube is highly desirable and we don’t have the heart to throw it away. We sell these at deep discounts. (Incidentally, most of the tubes I use in my own audio equipment are bargain quality. These tubes tend to work fine and last a long time.)
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Display Only: These tubes do not work for one reason or another and are fit only for display purposes. Typically these are types that are in high demand—otherwise they wouldn’t be worth displaying.
Photos
We also offer photos of most of the tubes on our website. Click “more info” to see the product description and find out if the photo is of the actual tube or of a sample tube from the lot. The photo will often be of one of the better looking tubes in the lot so it’s clear what tube type you are getting. For this reason, if cosmetics are important to you, please let us know so we can select tubes with that in mind. In some cases, we will also post additional photos in the gallery.
A Note about NOS
You may have noticed that “NOS” is not one of the tube classifications we use. We have chosen to avoid describing tubes as New Old Stock, since it is rarely possible to verify that a vintage tube has never been used. However, it is possible to test the tube’s strength (both in terms of current draw and amplification). Many tubes that bare signs of use on the pins, base, or flashing still test as strong as a new tube would test straight from the factory. And many tubes that we pull out of the correct boxes sealed from the factory test quite poorly. In addition to tubes degenerating due to use, tubes also degenerate as a result of minute losses of vacuum over time. No seal is perfect (referring here to the seal between the metal pins and the glass envelope), and inevitably tubes lose strength as the vacuum is gradually compromised.
On our website, we provide images to give you a good idea of the condition of the tube’s label, flashing, base, pins, etc. You can decide for yourself how important the tube’s appearance is. We also provide information on the tube’s test results. Generally—the more valuable the tube—the more detail we offer.