The Manual Bias system in our Dyna-70 Ultimate Upgrade Manual Bias ST-70 Amplifier has been upgraded with a new part. We introduced the Manual Bias system about 6 years ago using a single-turn Bourns Trimpot potentiometer for Bias adjustment in the Dyna-70 Ultimate Upgrade audio system. Those familiar with the Manual Bias Dyna-70 know we use 4 of these square body potentiometers on each Manual Bias Dyna-70 circuit card.

However, a drawback to using a single-turn potentiometer is the Trim pot is quite sensitive, and it‘s easy to under or overshoot the ideal Bias setting when adjusting the pot. We decided to change to a pot that was more user-friendly, enabling users to more precisely set their Bias values, while avoiding changes to the Manual Bias circuit card design.

We found a perfect replacement, also made by Bourns, but in a 4-Turn version that has a round body and is not as sensitive to adjust as the 1-Turn pot.  Now you can easily dial in the Bias set value you want.

This new round 4-turn pot is a drop-in replacement to the single-turn pot now in your Dyna-70 Ultimate Upgrade Manual Bias system.  We will phase out the square, single-turn pot and use the new round, 4-turn pots in all Dyna-70 Upgrade audio kits, all service and repair activities, and in all MALLC new Amplifier custom builds.

NOTE: This upgrade is applicable to the Manual Bias Dyna-70 Ultimate Upgrade Audio System; it is not applicable to the Automatic Bias models.