EJ Jurich

EJ Jurich

This is the home page for EJ Jurich,
author of Vacuum Tube Amplifier Basics.

There is an updated version of Vacuum Tube Amplifier Basics to be released under a new title. Although much of the information in the new book is pulled from the original book, the new book is being laid out in a more logical order. It will also include a more detailed example of amplifier design and construction.

Low Power Amplifiers

A project is in the design stage for an all triode Class A four watt per channel stereo amplifier based on a 2019 experiment. The book update mentioned above will need to be finished first.

Four watts may not sound like much power, but when paired with more efficient speakers, you can achieve appreciable volume. For home audio systems, operating high-power vacuum tube amplifiers can be expensive. Besides the initial cost of the equipment, there is the cost of replacing more expensive, higher power tubes as they 'wear out'. Also, higher power amplifiers draw more current with an associated higher electric bill.

Instead of thinking about volume, try thinking in terms of sound pressure level (SPL). It is the sound pressure in your ears that determines how loud something is. Operating high power amplifiers near full volume levels may generate sound pressure levels that can cause hearing damage. More on this can be found here.

Power output vacuum tubes are generally either single grid triodes or three grid pentode types. The majority of tube amplifiers use pentode type output tubes because of their higher power capability. Pentode power tubes are significantly more load sensitive than triodes. Because of frequency related impedance variations reflected back to a pentode output tube plate, speaker load matching can skew off the impedance matching curve.

Speakers are impedance rated at 1,000 HZ. Depending on frequency, the impedance then skews above and below 1,000 HZ. Pentodes are much more sensitive to this impedance change than triodes. Triodes maintain a better match over a wider impedance range. Impedance skewing can cause various speaker systems to sound dramatically different when connected to the same amplifier (one at a time).

In 2019, an experimental Class A triode output stage was wired up. I was interested to find out if forum posts and other claims of improved sound had any merit. It was a single channel output driving a single bookshelf speaker. What I found was an elegant, realistic sound.

Operating Class A single ended in itself provides a more natural sound than push-pull operation. The push-pull signal splitting phase inversion, then blended back together process is not perfect to begin with. Component values and tube characteristics that change with age add to signal errors1 in a push-pull system.

As a reference for amplifier power in a home, what would be considered a normal listening level, not really loud, about the same loudness perception as someone talking close to you, only requires about one watt of amplifier power. The use of a low power triode Class A output matched with a high efficiency speaker arrangement should produce a natural, rich sound.

EJ Jurich

1Errors such as bias on the output tubes drifting causing the blended signal to be clipped at the baseline.

Scam Warning

There is a site using the domain ejjamplifiers that may be using my name initials in an effort to fool you into believing I am associated with that site. This is false. EJ Jurich has no association in any capacity with ejjamplifiers. The registrar for ejjamplifiers is listed as GMO Internet Group, Inc. and appears to be located in Japan. Be wary of ejjamplifiers or any site address that use the initials ejj in a manor that implies it is related to EJ Jurich.

EJ Jurich has no association with sites offering free downloads of my book. Beware of sites that offer free downloads. Free download or torrent sites are notorious for passing malware on to you. Be very careful.

© EJ Jurich 2014 - 2024
PO Box 3416
Des Moines, IA 50316

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