Tung-Sol.com:: FAQs How do we match power tubes?

FAQs

Question:
How do we match power tubes?
Answer:
The Tube Matching System uses a test fixture that is based on the information provided in MIL-STD-1311 Test Methods for Electron Tubes. This document is the military standard for vacuum tube testing. This test fixture is connected to a special computer controlled switching matrix that selects each tube individually on a tray that holds forty tubes. This allows us to test and match large numbers of tubes to meet the demands of the musical instrument amplifier and hi-fi audio industries, as well as service shops and technicians that maintain this equipment. The system is powered by heavy-duty regulated power supplies that are continuously set and calibrated for each tube type through proprietary computer software that is referenced to a Hewlett-Packard/Agilent 34401A digital multi-meter. The calibration is tracable to NIST (National Institute of Standards and Technology). Each tube, when selected by the switching matrix, is put through a battery of tests, including inter-electrode leakage, positive grid current, screen grid current window, and high/low plate current limits, prior to the actual matching process. When the tube passes these tests, it is then matched to within 1 ma. plate current (Ip) and 100 microohms of transconductance (Gm). When the system has tested and matched the entire tray of forty tubes a sheet of labels indicating test results and matching information is printed by the computer. The tube tray is then removed from the matching system, replaced with another, and the process is repeated. The tubes are then put into pairs, quartets, or sextets with the labels indicating Ip and Gm attached to the boxes and the tubes banded together. The matching is very accurate and repeatable. This precision matching ensures that the sets of tubes will wear evenly, sound better, and last longer.

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