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Power tube matching process

The most effective way to match power tubes is to duplicate the amplifier circuit that the tubes will be used in. This is what we do when we are able to get that information from our customers. We use the custom test fixture (shown below) to do final check for all our power tube sets.

tctubes power tube matching test rig

After testing each power tube on our Amplitrex AT1000 testers (more info), tubes are given ratings for both current draw (mA) and transconductance (Gm). This information alone often gets us close to a matched set, but not always. So, we generally fill up the test fixture with 50%-100% more tubes than are needed in the target set. This allows us to select out the best matches at the most relevent voltages.

tctubes test rig loaded with 18 GE 6L6GC tubes

The test fixture is capable of running as many as 18 tubes in a single channel. This is a complete amplifier circuit with AC input and a huge output transformer so we can load test the tubes with a signal generator.

tctubes test rig meters closeup

All power supplies are fully regulated and the same grid voltage is present at each tube so we can directly compare all of the tubes with one another in real time.

tctubes test rig power supplies

The photo above shows some examples of the variety of power supplies that allow us to duplicate the voltages in our customer's amplifier. We have the ability to run up to 1000V on plate and screen with regulated power supplies, and up to 2000V on plate and screen with unregulated power supplies.

The screen supply is switchable. In one mode the screen voltage is derived from the output transformer as in most high end audio amplifiers. In the second mode the screen voltage is derived from its own dedicated power supply to imitate amps with large differences in plate and screen voltage.

This fixture is what we use to do final check-out runs of all our power tubes. If we have information on your amplifier, we will run your tubes at those voltages. If we do not, then we will run the tubes at our best guess at what those voltages might be.

TC Tubes specializes in precision testing and matching of vintage and new production vacuum tubes for guitar & bass players, audiophiles, and DIY tube audio enthusiasts. Our website features secure payment options and fast, convenient shipping around the world.

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