Douk Audio CT1-BOX Dual Bias Current Probe Tester with VU Meters Review

The Douk Audio CT1-BOX is a tube bias measuring tool priced at $56.99. It is a pair of probe testers plus a meter box, designed to measure the cathode current of power tubes at the low-voltage side so the bias current can be read off directly.

The unit suits a list of common octal power tubes: EL34, KT88, 6L6, 6V6, 5881, 6550, KT66, KT100, KT120 and 7027. Each probe uses a ceramic socket with thick gold-plated pins, chosen for service life and contact quality, and copper wiring runs through each tester, which the maker says is hand-soldered. The meter box carries two large current meters with a 100mA maximum range, one for the A probe and one for the B probe.

Using it is a deliberate process: power off the amplifier, connect the two probes to the A and B sockets of the box, pull the power tubes and seat them in the bias probe sockets, insert the probe leads into the amplifier's tube sockets, then power up and let the tubes warm for about five minutes before reading. The left meter reads the A input and the right one reads B; the listing advises that identical readings are ideal and that a difference of no more than 2-3mA is a good balance between tubes. The tube socket cable is 23cm long, the box measures 150 x 106 x 70mm and weighs 500g, and the pack contains one pair of probe testers and the current meter box.

Douk Audio ships worldwide with free and expedited options and country-dependent pricing. Orders under 2kg go by airmail in 10-25 days, above that by DHL, UPS or FedEx in 5-8 days; with a 500g net weight and a 1000g package weight the CT1-BOX ships by airmail. Import duties and customs charges are the buyer's responsibility. All items carry a 30-day free return or full refund and a 1-year warranty, excluding orders placed by mistake, man-made damage or misuse, a subjective change of mind, and anything else outside the warranty terms.