Tube Amplifier Bias Adjustment

Output tubes drift as they age. The bias current wanders off the manufacturer's specification, and the amp starts to sound soft or hazy, or runs hot enough to eat through tubes faster than it should. Setting it back to spec is a meter-and-screwdriver job on the bench, and it is worth doing before you start replacing tubes that were never the problem.

This is an in-store service at our Chestertown shop. Bring the amp to us and Mike will set the bias on each output tube. Buy it here and we will contact you to arrange a time.

Free When You Bought Your Tube Amp From Us

If you bought your tube amp from The Listening Room and it has adjustable bias, your first bias adjustment is free. You do not need to order it here. Contact Mike after your purchase and he will set a time for you to bring it in.

What's Included:

• Warm-up to operating temperature before anything is measured, so the reading is the one the amp runs at
• Bias measured on every output tube, with no music playing and the volume down
• Each tube adjusted to the specification for your amp and the tubes in it
• A check that your tubes are seated in the positions they are labeled for

When Your Amp Needs It

Mike's guidance, from his own bias walkthrough: check it about every six months, any time you hear a channel imbalance, and always after you replace a tube. Every tube has slightly different efficiency, so a new tube needs its bias set.

Before You Come In

Bring the amp itself. You do not need to pull the tubes or bring anything else. If you have recently swapped in a new set of output tubes, say so when we schedule. If you are not sure whether your amp has adjustable bias at all, call or text Mike at 410-239-2020 before you order and he will tell you.

No product will be shipped to you as part of this listing. This covers the bias adjustment only. After purchase we will reach out to set a time.