Fender Blues Junior adjustable bias mod.
The Fender Blues Junior and Daville is known as a fixed bias amp. Unfortunately this term is widely misunderstood and doesn’t mean that it doesn’t need to be changed! We get many people who have changed output valves, and within a matter of weeks are contacting us as the amp is overheating, valves are glowing bright red or the sound has gone really bad.
The term fixed bias really just means that component values need to be replaced to match the new bias level for the replacement set of valves. Whereas an adjustable bias amp simply has an adjuster control to save the need to change out parts.
Ever Fender Blues Junior we’ve seen through the door has a biasing set at between 30% and 60% higher than the Nominal setpoint that valves are usually biased to based upon plate voltage and power using ohms law.
It’s straightforward to add a biasing trim control.
We would advise that this is carried out by an experienced person such as ourselves due to the high voltages present on the PCB. There is also a very high chance of damaging the output valves and possibly transformers if the mod isn’t carried out correct or you short out other wiring inside.
To read about the reason amps are biased and what it is about you can read our biasing post here
For the price of a standard service and around £6 worth of parts we can carry out a service to check for any existing damage, check the valves, Deoxit cleaner the pots and carry out the bias mod.
A full MOT for your blues junior and a better environment for your valves to run in!