Bias guitar amp with oscilloscope
For many years both Fender and Marshall did not provide any method for output valves to be independently calibrated or balanced. This is similar to having balanced pistons in a vehicle engine, plus the ability to tune the engine. Providing the amp circuit is correct and there are no component faults, a valve amp performance is dependant on the correct balancing and matching of the output valves. Early Fender and Marshall 60 Watt to 100 Watt models commonly used by professional musicians will be used as examples. This page will focus on resolving some of the contradictions and hopefully give a broader understanding of guitar amp design and service. There are many web sites and books that have information on servicing valve guitar amps. This paradox insures that any successful marketed product will always have design contradictions. For any product to be successful in a capitalistic society, the manufacturing cost must be a fraction (1/10 to 1/100) of end user price. Computer operating systems are another example. Many who service their own motor vehicle can be heard cursing those who designed it. The same can be said of almost any mass produced product. These statements are not intended to be derogatory, but statements of fact. Similar to a vehicle that cannot exceed the speed limit due to its mechanical limitations.
#BIAS GUITAR AMP WITH OSCILLOSCOPE FULL#
Most valve guitar and bass amps rarely perform at full capacity, which inadvertently protects the speakers. Also the limited circuitry can not drive the output valves symmetrically unless modified.
This is similar to a vehicle engine where the designers applied no thought for the engine to be serviced or tuned. In most cases the output valves are unable to be readily calibrated and balanced. No allowance was/is made in the majority of guitar and bass amps for ease of service.
The most popular of the larger models including the clones had/have 4 output valves in parallel push-pull that produce 60 to 100 Watts. Fender and Marshall were/are the most renown and copied amplifier brands.