In part two of my series of articles on tube amp myths and misconceptions I'll cover three more common tube amp misconceptions: 1. I don't need to bias my amp! 2. Never Replace Capacitors in a Vintage Amp!
I Don't Need to Bias my Amp!
Some Players don't believe in biasing their power tubes. They just pop new ones in. This can lead to bad tone or even worse--- severe damage to the amp. In a fixed bias amp it is essential to bias the power tubes. You are setting them to their desirable operating point and if they are no set properly it can be bad for the tubes, transformers and worst of all your tone. If the bias is cold the amp will sound dead and not have much power. If the tubes are biased too hot they are destroying themselves and can damage your transformers when they blow!
Never Replace Caps on a Vintage Amp!
While an amp with all original parts sells better it definitely won't sound better than an amp that is working properly. Caps are not meant forever; they degrade over time. Caps rely on their chemical composition to store voltage but because of entropy those chemicals break down making them less able to store voltage and causing leakage. Some types of caps go bad faster than others. Electrolytic caps are the ones we worry about in tube amps. Other types fail more rarely and only need replacement if they are clearly defective. Electrolytic caps need to be replaced every 7-10 years for the best performance. An amp with older caps may still play but won't perform like it is meant to. Bad caps can lead to hum, lack of power, lack of gain, and a weak bottom end. The amp may not every operate.
An original cap is not original because it is worn. You would not refuse to replace the tires on your 65' Mustang because they were original? Replace those caps and breath life back into your amp!