Tube Replacement

The larger power tubes need replacing every couple of years, if the amp is used frequently .The smaller preamp tubes will generally last 2-3 times longer than the power tubes. Bad power tubes will have low level o/p , sound flat and lifeless and ,have low end microphonic rumble .Bad preamp tubes are either noisy or microphonic.To check for microphonics , turn the amp up full and tap each tube with your index fingernail.Tubes that resonate are microphonic and should be replaced.

Biasing Output Tubes

Biasing sets the operating level of the O/P tubes.Bias voltage on the grid affects how much current can flow from the plates of the tubes.The more negative bias voltage on the grids , the less current flows from the plates and conversely, less negative bias allows more current flow.There is no exact negative voltage to bias your amp. Basically you want enough voltage to keep the tubes output current within its operating parameters but not so much that you get crossover distortion. Some amps are fixed bias and require no adjustment, but it is better to be using matched output tubes in these amps.

Filter Capacitors

The filter caps show signs of wear when an annoying low level hum starts becoming apparent in the background. This usually happens when the amp is 15-20 years old. Other signs include a bubble or rupture around the ends of the cap. Replacement of these caps will bring back life to the sound. The bass will be more defined and focused, while the mids and highs will be clearer, have more depth and a wider soundstage. You can use slightly larger value replacement caps if you would prefer a more bassy sound.

Coupling Capacitors

Upgrading these caps is a service we provide for hi-fi tube gear and guitar amps. These caps are the links between the valve stages in signal and coupling positions .They block the dc voltages between the stages while allowing the audio signal to pass through.The ability of the capacitor to pass the signal without sonic degradation is whats required.Manufacturers tend to use generic types like Wima, Solen, Illinois etc, which provide average performance while upgrading to high end caps like Jensen PIO or V-caps teflon types in hi-fi gear or the Sozo and Jupiter vintage caps for guitar amps will greatly enhance sonic performance. www.v-cap.com