Douk Audio CT1-BOX Bias Current Probe Tester 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.

Specifications

How it compares

The CT1-BOX is the group's only test tool, and it is aimed at tube amplifiers with 8-pin power tubes such as the EL34, KT88, 6L6, 6V6 and 6550. The Matched Pair 7-Pin GE JAN 5654W Vacuum Tubes review ($34.99, $22.00 less) covers a different family: 7-pin small-signal tubes for 6J1, 6AK5 and EF95 sockets, none of which the CT1-BOX page lists, so the two are not a matched set.

If your upgrade path is solid-state rather than tubes, the Sparkos Labs SS3602 Discrete Dual Op Amp (1PC) review ($89.99, $33.00 more) is a drop-in op-amp swap for DIP8 sockets, and the CT1-BOX has nothing to measure there. Choose the CT1-BOX if you re-bias an amplifier with 8-pin power tubes and want to read both tubes at once; skip it if your amplifier uses small-signal or other tube types that the page does not list.

Shipping, returns and warranty

• Shipping: Douk Audio's current shipping page says orders are generally processed no later than the next business day and arrive in 2-8 business days, with duties, taxes and customs fees included in the checkout price unless noted otherwise.
• Older shipping terms are still online: airmail at 10-25 days for parcels under 2 kg, DHL, UPS or FedEx at 5-8 days above that, and a line saying the store is not responsible for import duties. Check the delivery estimate and any duties at checkout.
• Returns: ask within 30 days of delivery and wait for approval before sending anything; an approved return has to ship within 7 days. Items need all packaging and accessories and no excessive wear, or the store can refuse them or refund part of the price. Refunds go to the original payment method after inspection.
• Not refunded: original and expedited shipping, duties, taxes and customs charges, unless the law requires it or the store made the error. The return page does not say who pays return postage, and the older refund page excludes mistaken orders and change-of-mind returns from free after-sale service.
• Warranty: 24 months from purchase for manufacturing defects, with free repair, a replacement unit and free shipping both ways for covered repairs. Drops, liquid, DIY repairs, lightning, extreme temperatures and misuse are excluded (partial fees may apply), and damage from weak packing on the way back may not be covered. The older refund page still says 1 year.
• Seller: the site is run by Shenzhen Anba Technology Co., Ltd (Shenzhen, China) and HONGKONG LONGSHENG Import and Export Trading Co., Limited (Hong Kong); support is by email at [email protected]. These terms cover orders placed on doukaudio.com; other sellers apply their own.

For this product, the page lists US, UK, EU, AU and Other under 'Shipping to' and shows Free Shipping, 2-8 Days Arrival, 30-Day Return and 2-Year Warranty badges near the price.