Vacuum tube testing & matching

Tube Testing, Matching, and Ordering Info

Standard Test $4 per tube. No minimum order.

All tubes are screened for shorts, gas, and heater-to-cathode leakage (unless it’s a directly heated tube), and then tested for emissions and transconductance (Gm) on an Amplitrex AT1000 (in some cases on a Triplett 3444). Measurements are compared to published standards and/or the Amplitrex database for emissions and conductance. Diode sections and tubes are measured for peak forward and reverse current. Full-wave rectifier tubes (like 5U4, 5Y3, GZ34) are measured for peak forward and reverse voltage drops for both sections. All tubes (unless you specify Autobias mode) are measured in Fixed Bias mode, which is our default mode and the one we consider most valid in general most of the time. See the Bias page for details.

Standard Test Results You Will Receive (except diodes and rectifiers. See above.)

Emissions (anode current) New Spec and Actual

Transconductance (Gm) New spec and Actual

Transconductance (Gm) Actual as a percentage of New

Our ratings scale (Based on Gm % of New)

This is our scale and somewhat arbitrary, although it is similar to what many tube resellers use. We consider most tubes under 70% of new as Weak, although some knowledgeable industry sources use 50% as the lower limit of acceptability for Good. Some tubes that test at 50% will work fine in one application and not work in another. Generally, though, they would be considered weak in terms of emissions.

69% and below = Weak

70%-74% = Good

75%-84% = Very Good

85% and higher = As New

We just test your tubes and give you the data. It does not mean, for example, that you cannot or should not use tubes that test under 70%. They might work fine in your application, be good for spares, or be good for routine equipment testing that avoids using good, expensive tubes.

Optional Tests and Services

Noise/Microphonics $2 per tube

Most critical for preamplifier tubes, this test requires additional setup time and is a subjective one to detect and rate noise and microphonics. Ratings are Very Low, Low, Moderate, and Excessive. You receive separate results for noise and microphonics.

Tube Matching $3 per pair

We can test your tube pairs/quads and rate their degree of matching, and we can take any number of tubes and segregate them by the usual matching parameters (Gm or anode current). This service is $3 per pair in addition to the Standard test. Typically, triodes are matched for Gm and for balance between sections. Power tubes are typically matched for anode current. Generally, an excellent match is when tubes are within 10% of each other for anode current and then within 5% for Gm. (Matching power tubes normally is not as critical as preamp tubes if the amplifier has separate bias pots for each tube, but we agree that starting with matched power tubes is the ideal). We include a data sheet showing the results and matching data for each pair or quad.

Gain and Plate Resistance $2 per tube

For even more matching precision (triodes only), we provide tube gain (Mu) and plate resistance (Rp) measurements.

Directions for Sending Your Tubes

Please print and fill out the PDF on the Tube Test Order Form page, and include it with your tubes. Ship via a trackable service, insured, as we cannot be responsible for tubes lost or damaged while in transit to us. Please securely wrap your tubes in bubble wrap or similar and then place in a corrugated box. Make sure there is cushioning all around the tubes. Wrapping paper or newspaper work well.

Payment, Invoicing, and Return Shipping

We’ll test your tubes, usually the same day we receive them, and have them back on their way to you the following business day. We accept PayPal and most credit cards via PayPal. A PayPal account is not required to use a credit card. We’ll send you an invoice prior to return shipping. We use USPS First Class Package. It’s trackable, with delivery six days a week. Best of all, ours is a $6.99 flat rate to the lower 48 states, whether it’s one tube or ten.


We prefer not to test any tubes that are not identifiable from the manfufacturer’s markings on the tube, as we don’t want to smoke your tube or our equipment.

We use established test procedures and trusted equipment to rest your tubes safely. Our liability is limited to replacement of your tube in the unlikely event that we damage it. Western Glow Tube Service is not liable for any indirect or consequential damages arising out of testing your tubes. In no event shall our liability exceed the fair market replacement cost of your tube, once we establish and agree that we damaged it.

Our testing services generally focus on tubes from about 1945 and later made for use with guitar and bass guitar amplifiers, audio amplifiers, and tuners. We also test old radio tubes from about 1930 and short-wave radio receiving tubes from about 1940. Please contact us by email first ( if you need testing of uncommon tubes, especially short-wave transmitting tubes. We will confirm with you if we can test them.

Vacuum Tube Testing, Matching, and Sales