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Building Vacuum Tube Amplifiers

Home Built Audio Systems

Building Vacuum Tube Amplifiers

Home Built Audio Systems

There could be a few reasons one might include vacuum tube amplifiers in their audio system. Aesthetically they look cool with their mechanical appearance and glowing tubes, sonically they are a pleasure to listen to. Class A single ended amplifiers in particular are noted for generating second order musical harmonics. Virtually all digital audio formats use some form of compression to save bits and bandwidth removing nuances considered too low to be heard. Some of the nuance removed includes harmonic content. Harmonics give music depth, regardless of claims that they are too low to be heard harmonics are a key ingredient of music. Using a Class A analog amplifier as the last link driving your speakers will in effect replace harmonics removed during digital compression processes.

building your own vacuum tube amplifier. Illustration by Mark Jurich

Vacuum tubes operate with substantially higher voltages than solid state amplifiers. When powered up voltages of 400 volts or higher is not unusual. Even after it is shut down capacitors in an amplifier may be holding a charge. Always consider the possibility of shock and be careful where you put your fingers.

If you are new at building your own amplifier, the best advise is take your time and work carefully. Do not skimp on chassis size, a little extra room is better than components crammed on top of each other in a tight space. Wires should be run first positioned flat against the chassis. Components such as resistors and capacitors are positioned over wiring. Do not depend on the chassis for ground circuits. Many terminal strips have a lug common to the mounting foot as a ground connection. Always connect all ground circuits together with wiring.

If one is designing their own circuits, they must have the electronic knowledge to do so. You don't have to be an electrical engineer, but must have a basic understanding of electronic circuits and calculating circuit values. Basic test equipment such as a volt-ohm meter, audio signal generator and oscilloscope is required to check circuit operation. Measuring distortion requires a distortion analyzer. Computer software can be used, but depending on computer configuration results may not be accurate. A simple solution is to use pre-designed tested circuits.

One needs to have decent metal working skills such as drilling holes and using punches for larger holes. An amplifier chassis can be either aluminum or steel. Aluminum is easier to work with, but aluminum is not as sturdy as steel. A steel chassis does not twist as bad as aluminum and holds more weight. Weight can be a factor with larger heavy transformers. If the budget permits, a plate can be machined professionally with engraved lettering. Use the 'Supplier Listing' link below.

Without prior soldering experience it would be wise to practice soldering wire connections on some practice terminal strips. Sooner or later bad solder joints will become problematic. For best results use lead based solder with a rosin core such as Kester 44. Lead free solder will not last and acid or water soluble flux is corrosive. Water soluble flux generally uses organic acid activators as the flux. If not completely cleaned off with water, any trace of water soluble flux will over time corrode and damage electronics.

For the best sound use a decent set of speakers. Main speakers for left and right stereo should provide a frequency range around 40HZ to 20KHZ or better. There are reasonably priced bookshelf speakers that provide this range. For media use such as watching movies to experience those explosions and other sound effects include a sub-woofer. For music a sub-woofer tends to throw tonal balance off. Music usually sounds most natural just using the two main speakers.

Speakers come in all flavors, reasonably priced to horrendously expensive. When purchasing speakers keep in mind that speaker specifications are measured in a near acoustically perfect chamber. Generally speaking the average home does not have acoustically perfect rooms. For use in an average home spending hundreds or thousands on high end speakers may not provide what one expects. Placed in an average room those high end specifications do not mean much, performance will not be the same as measured in the acoustic chamber. That being said spending a bit more on recognized high quality speakers may produce a little smoother sound. Read reviews.

High power vacuum tube amplifiers are expensive to buy or build. When selecting speakers a SPL rating of around 93db or higher will require less amplifier power. The higher the speaker SPL rating the less amplifier power you need. This provides savings of the initial amplifier cost, lower electric power expense and lower cost output tubes when replaced. For more information use the 'Power Versus Loudness' link below.

Class A, Class AB, Class D
Amplifier Class Comparison

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A Definitive Experiment
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