The first part of this blog post covers when to change the vacuum tube in the Le Preamp Series preamplifiers.
The vacuum tube is a sturdy device, but it does wear out over time. Unlike power amp tubes, preamp tubes do not require frequent replacement or replacement as preventive maintenance. But, in order to keep Le Preamp (LeClean, LeCrunch, LeLead and LeBass) in perfect working condition, you may need to replace the tube someday. We have taken great care in selecting a commercially available tube selected by a company renowned for its exceptionally low failure rate (Ruby 12AX7AC5 HG) and tuned our design for what we feel gives the best tone and response.
Most of the time, the tube won’t fail totally and suddenly. Instead, the tube will degrade gradually. Le Preamp will continue to work, but will loose gain, dynamics and harmonic richness. Eventually, the sound will become flat and lifeless.
Because of the gradual nature of this degradation, it can be hard to know exactly when the tube needs to be changed. So the general answer is: when you feel Le Preamp is not sounding or reacting to your playing as it should.
How often this should be done depends on many factors, like the original tube quality, the rate of use (the tube does not wear out if not used and stocked in good conditions), the conditions of use, and down the line, your personal taste. This makes it hard to indicate exactly how often the tube needs to be changed. The following guidelines can be given, but keep in mind that they may have to be adapted to your particular situation.
Generally speaking, a tube can give you several years of pleasure before needing a change. A hobbyist musician using LePreamp on occasions may not even need to change it at all. On the contrary, a regular musician, using LePreamp everyday, who wants to always keep the best tone possible, may want to change it more regularly.
The second part of this blog post covers how to change the vacuum tube in the Le Preamp Series preamplifiers.
Changing the tube is easy and does not void the warranty, but should only be done by a qualified technician, considering the presence of high voltages in the unit. This procedure requires the tube to be cold and the unit disconnected to any power source and other audio or MIDI connection.
The tube used in Le Preamp is a Ruby 12AX7AC5 HG. You can also use any standard 12AX7 tube as a replacement.
1. Disconnect the power cable and every other connection to the device.
2. Install the device upside-down on a soft, clean and protective surface to avoid scratching the unit.
3. Using a Philips screwdriver, remove the 4 screws on the bottom.
4. Remove the cover. It can sometimes be stuck and hard to remove. Loosen the 5 X 1/4″ jack connectors hex nuts (use a11mm socket wrench). If needed, you can also use a small flat screwdriver as a lever through the screw holes, again to avoid any scratch on the unit.
You should now have access to the tube, through the big hole at the center of the PCB
5. Grab the tube, and make it move from side to side while pulling it out of its socket.
6. Before inserting the new tube, locate its missing pin. Insert the tube so as to match this missing pin with the indicated location on the tube socket:
7. Install the cover and screw the 4 screws back. If you loosened them, tighten the 5 X 1/4″ jack connectors hex nuts back. By hands first, then with a socket wrench (1/8 or 1/4 turn is enough).