Tube Matcher
Here's something every tube enthusiast could use: an idle current tube matcher. Ever since the Sophia and Maxi tube testers have been available, I've wanted one, but they're too spendy for my pocket book. A good transconductance tube tester is a must for testing opens, shorts and for mutual transconductance, but matching output tubes for push-pull amps should really be performed at normal operating voltages while matching idle (bias) current. This tester can test a maximum of four tubes at a time for idle current using the low voltage 1 ohm 1 % cathode resistor method. A VOM is required for measurement. All cathodes are brought out to banana plugs for simultaneous testing. A 4 way selector switch, switches a common test point between 1 of the 4 cathodes for single tube measurement. It's designed to test standard octal pentodes of 6L6, 7581, 6V6, 6550, EL34, KT88 and KT66. It has two separate 3-prong AC cords. One for the heater tranny which yields a constant 6.3 heater voltage and one for the power tranny that can/should be plugged into a Variac for a variable B+ voltage. The bias voltage is variable too. Thus a complete family of characteristic curves can be generated for matching power tubes at various operating points.
When your repairing tube amps, you'll soon find that having the ability to swap out suspected bad transformers quickly and safely with a known good transformer is an essential debugging tool. A unique feature of this tester is that all voltages, B+, Bias and Heaters, are brought out to banana plugs for easy and quick power transformer substitution or for supplying the necessary voltage to power your own tube design prototype.
