NOS Tube Store: Test Bench

Koray attentively testing a NOS 211 power triode on the Amplitrex and a AVO MKIV aside.

Why the Amplitrex AT1000?

Because, we would like to;

- use a tester designed with audiophile and musical instrument tube testing in mind

- test tubes at real-world power levels, the AT1000 can operate tubes at up to 500V and 160 mA - the power levels output tubes see in real-life, unlike many vintage testers that have only 165 to 250 VDC available for testing

- read true emission results in DC milliamperes, and true transconductance in mA/V (1mA/V=1000 uMHOs) using a 1 kHz AC signal. The Amplitrex offers laboratory grade testing under microprocessor control and makes it possible to check a tube according to the original manufactures design specifications taken directly from vintage tube data books. Many vintage testers were designed for television and radio tube testing. Some do not even test transconductance, or GM, they only measure simple cathode emission. Even some better vintage testers give you the results only in arbitrary, meaningless, units

- measure Heater-to-Cathode Leakage, Emission and Gas thoroughly

- match tubes not only by plate current (emission), but also by transconductance, and most importantly at normal current and voltage levels, faithfully reproducing the actual operating conditions found in many amplifiers, preamps and other equipment

- be able to listen to tubes for selecting only microphonics and noise free ones to offer the customers

Testing Process

Each tube’s electrical properties are analyzed for heater-to-cathode leakage, shorts, grid leakage (gas test), plate current (emission), and transconductance is measured. Results are noted on a label for each box. Matching is within 10% plate current and 5% transconductance unless otherwise noted. Given the large volume of our stock we often can match much tighter than this.

We screen all tubes for noise and microphonics however, the best test is always in-circuit, and we can not accommodate all tubes. Circuits operate differently, and we take exchanges if a tube is found to be noisy when installed in your particular application.

Testers under use:

Amplitrex AT1000

AVO CT160

AVO VCM Mark IV

Hickok Military TV-2 and several TV-7 types

Hickok 752A

B&K 550

TAYLOR 45C