John Gatski is the Publisher & Executive Editor of Pro Audio Review.
With the heyday of audio tubes well behind us, tube amplifier enthusiasts have spent years buying up and stockpiling new and used tubes. Unless you are handy with multimeters and practiced at amp anatomy, however, you seldom know whether tubes were matched for your particular amp. Throw in multiples of four unmatched tubes, such as an old hi-fi or high power guitar amp, and good performance is not always assured.
Features
Along comes the Maxi-Matcher to save the day. Distributed by parts distributor Magic Parts, the Maxi-Matcher is a handy, comprehensive tube tester that allows for precise matching of output tubes in terms of bias and transconductance.
The $450 Maxi-Matcher contains four tube sockets and can test output tubes, such as the popular 6L6, and 5881, 6V6, 6550, EL34, KT88, EL84 and 7027s. A fifth socket tests for shorts. Adapters are available for almost any type of output tube, including 7591, 811 and 885.
Controls include an off/on switch, tube socket select, plate voltage select (325 and 400V DC), bias/transconductance select, bias voltage adjustment (-60, -48, -24, -12). A digital meter displays the plate current in millamps and can be used for comparing and matching tubes and as a guide for setting bias.
In use
To make it simple for novices or tube fanatics to match their tubes, a chart affixed to the Maxi-Matcher shows the aforementioned optimum plate voltage, bias voltage and the corresponding plate current ranges and transconductance factor for each tube type. Pop in a tube (or two, three or four) and set the switches as prescribed for its type. In a few seconds, you'll see how close the tubes are in performance, and whether they perform within spec range, based on their type.
Matching tubes optimizes performance for fixed bias or self-bias tube amps. Correct bias voltage means that the tube is drawing the desired plate current and putting out rated power at the lowest distortion. Transconductance indicates the efficiency of the tubes to put out rated power.
I tested 50 tubes, including many 6L6s and 6V6s for my antique Fender guitar amps, and 6550s and KT88s for my MacIntosh MC275 monitor amp, as well as a couple of EL34s.
Summary
The Maxi-Matcher made the task easy. For self-bias amps, tubes that are matched and perform within the specified range, means no amp bias adjustment is needed. For fixed bias amps that either have an adjustable bias, or the bias voltage is altered by a bias resistor change, some adjustment still may be needed, but at least with the Maxi-Matcher, you will know that you started with equally performing tubes.
It is not cheap, but if you are into stockpiling output tubes, the Maxi-Matcher tube matcher is well worth the price. For more information, contact Magic Parts at 800-451-1922.
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