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frequently asked questions

Checking & Adjusting the Adaptive AutoBiasT Board

Before you begin: Please note that most customers will NEVER need to refer to this page. Making adjustments to the Adaptive AutoBias board when none are needed may have an adverse effect on the sonics of your amp. Also, if you make a mistake and turn the AutoBias setting too high, you may cause severe damage to your tubes or even the amplifier, and such an event would void your warranty.

Consult your local PrimaLuna Partner or contact PrimaLuna USA directly before attempting the procedure outlined below.


You will need:
A multimeter that measures milliVolts (mV) and a philips screwdriver. If you have multimeter leads that can clamp down on areas that makes this easier, but they are not necessary.


1. Lay your PrimaLuna upside-down on a soft cloth. Remove the bottom cover. Keep all tubes installed in the amplifier. It's easier to keep the amp level if you have the tube cage on.

2. Plug in the PrimaLuna and turn it on. Give it a few minutes to warm up. Take special care, as you are dealing with high voltages!

3. Touch the black lead on your multimeter to the wire bridge located near the smaller tubes
(see picture below)

4. Touch the red lead on your multimeter to each of the four tube sockets which are attached to the gray wire running from the AutoBias board (see picture below)

5. Measure each power tube. For the ProLogue One, Four, Six, or DiaLogue One, make note of which tube measures lowest. On the ProLogue Two, Five, Seven, or DiaLogue Two, make note of which tube measures highest.

6a. For PrimaLuna amps that come stock with EL-34s, touch the red lead to the tube that has the lowest test measurement. Adjust the small white pot located on the end of the AutoBias board by turning it with a philips screwdriver until the multimeter reads 350 mV (.350 v). Refer to the picture below. If the lowest tube already measures at 350 mV no adjustment is needed.

6b. For PrimaLuna amps that come stock with KT88s, touch the red lead to the tube that has the highest test measurement. Adjust the small white pot located on the end of the AutoBias board by turning it with a philips screwdriver until the multimeter reads 400 mV (.400 v). Refer to the picture below. If the highest tube already measures at 400 mV no adjustment is needed.

You will notice the reading will go up and down as you measure. This is completely normal. Do not stress if you can't get your amp to the exact number indicated above. Just get as close as you can.

7. Once you have finished making the adjustments, turn the amplifier off, and put the bottom cover back on.