All Manley amps have individual trimmers that are used to adjust each output tube's bias voltage. It is like setting the idle on your car.
Optimum bias provides the best balance of tube life and sound quality.
Manley Lab's amp designs operate the tubes cool at low current so that the they typically last 5 years or longer if the bias is correct. Although, sometimes tubes have a short life and others may be fine for 20 or 30 years. Individual bias trims eliminate the need for expensive matched sets of tubes or the need to replace all the tubes if one tube has a problem. When you need tubes, give us a call and let us know the number that is hand written on the tube as we have some special tube batching jigs we've been using for years. Yes, we do sell tubes - the good ones.