Plate resistors are notorious for causing hiss and crackling as they age and begin to fail.Electro-Harmonix has released a low noise, low microphonic version of the 12AX7 that meets all specifications required for the tube to be designated 7025. Other components can cause noise problems that may be blamed on a bad tube. Tubes designed for high gain can exhibit more background noise.

Typically, you will notice this as a soft hiss or white noise. If the tube has good tone at lower volumes and is free from unwanted noise, you use it in a less sensitive part of the circuit, such as tone recovery or phase inverter applications.Īll tubes have a certain noise floor this is the inherent background noise that the tube makes in operation. Keep in mind that doing so can actually damage the tube and make it more microphonic or cause it to fail if you hit it real hard.Ī microphonic tube will ring, howl or produce general feedback problems. When used in this application most tubes will generate some noise if you tap on them with a pencil during operation. Input pre-amps are the most sensitive areas of the amplifier. You just have to screen them a little closer and determine where they are best suited for use. Usually a compromise is arrived at in the search for premium tone. Some tubes were clearly better suited in one application or usable in both.Īll tubes were used at the input amplifier stage of the amp since this seems to be where most people develop their perceptions of how good a pre-amp tube is.īack to top What Makes A Good Tube The musical detail or ability to reproduce the sound of the instrument is a key factor in assessing a tube for guitar amplifiers.Įach one has strengths, weaknesses and certain factors that contribute to its overall ratings. This allows the high power, high gain crowd and the more conservative players to get the fairest evaluation possible.

One was a 100-watt Trace Elliot Speed King with 4 x 12 cabinet, and the other was a Fender Blues Junior combo amp. The aim was to get a sample that would be practical to work with but allow for variations in the tubes or prevent picking the only dud in a lot. The tubes used in this review were selected at random from s inventory of untested tubes.įor each tube used in the test, two were taken since there was no pre-screening involved. To view this site, you must enable JavaScript or upgrade to a JavaScript-capable browser.

7025 Tube Equivalent Free From Unwanted.

7025 tube equivalent