Getting Back That “Sound” in Vintage Guitar Amplifiers
In terms of vintage guitar amps and other vintage gear, restoration of sound quality is the main objective. What this usually entails is replacing all the parts that tend to fail or deteriorate over time.
On equipment over about 25 years old, this almost invariably involves the replacement of the electrolytic capacitors in the power supply section. These are the first to fail. When the amp seems to have lost its punch and/or has a slight higher-pitched hum (120Hz) in the background, it’s an indication that the capacitors that filter out the hum and store voltage that is delivered to amp circuitry have lost their ability to function properly The first step is to replace them. This type of capacitor is also found in the pre-amp stages and in the bias circuit of tube amps, and should be replaced as well.
To preserve that cherished tone produced by vintage guitar amplifiers, sometimes it’s best not to replace all of the capacitors found in the pre-amp and tone control stages, but to replace only the ones that tend to fail or degrade sound quality. Replacements should be selected that match the tonal qualities of the originals. Brands such as Mallory, Sprague, and Xicon, among others, offer capacitors that suit this purpose. If desired, a vintage amp’s tone can be altered or enhanced by using certain brands and types of capacitors.
Most other parts in vintage amps hold up remarkably well, even after more than 50 years of use. Transformers never need to be replaced, unless they short out. I believe that good working transformers should never be replaced with so called modern “premium” types. Part of the magical sound of a vintage amp can be in that crusty old output transformer. Besides, collectible vintage amps are worth more with original transformers. It should be noted that replacing parts such as capacitors, which are known to degrade over time, often will enhance the value of a vintage piece substantially.
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