With the ever-so-wide quality range of current production tubes, and the "spin the roulette wheel" world of NOS and vintage used tubes, it pays to know how your amplifier is handling those expensive tubes you are putting into it. Even with tubes that were "matched" from the factory, you can still wind up with problems if you just plug 'em in and go. Enter the SRS Original BIASTOOL- a great device that no tube amplifier owner should be without- even if you decide to let the pros to all of the work inside of your amplifier, the BIASTOOL is an invaluable item, providing a quick indication of how your expensive output tubes are working in your amplifier...
   The BIASTOOL testing probe works with most tube amplifiers, including Marshall, Fender, Ampeg, Hiwatt, Peavey, Soldano, and many others, measuring the amount of current which actually flows through your power tubes, using your volt/ohm meter, which can be purchased separately for as little as $24.95 or you can purchase a full kit from SRS...There are many types of BIASTOOL test probes available: Version 1, the original BiasTool mA, is for owners of meters which can read current in DC mA directly, Version 2, the BiasTool mV, which is designed for owners of meters which do not have the capability of reading current directly, as well as the DualBiasTool, which utilizes two of our mV probes and a rugged switchbox- this unit tests two tubes at a time, or both sides of a push/pull amplifier without powering down and switching tubes or sockets! There is also the MiniBiasTool, which is designed solely for the 9-pin mini output tubes such as EL84/6BQ5...
   The BIASTOOL is an indispensable piece of test equipment, used to check and set the "idle" of your amplifier, to guard against premature power tube failure due to overheating, and to get the best tone out of your amp...Setting your amp bias to run too cold will make it sound harsh and gritty, and setting it too hot will lead to premature power tube failure, and poor, muddy tone. The BIASTOOL will help you keep your amp running the way it was designed to run, and sounding the way it was meant to sound!
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  This quality piece of equipment definitely falls in the category of items that require a working knowledge of amplifiers, especially if you are planning on making the adjustments yourself- we strongly suggest that if you are not up to speed on such things, that you only use the probe as a measuring device, and enlist the services of a pro for actual bias adjustments- in this way alone, it can save you hundreds of dollars over the life of your amplifier, by keeping your output tubes from failing early due to poor biasing and overheating- it could even save you the cost of a new output transformer! If you are aware of the potential hazards which exist inside of a tube amplifier chassis, and are amp tech savvy, you can save yourself the cost of a bench charge every time you re-tube your amp, saving you hundreds more!
   Keep your new or vintage tube amplifier sounding great, and get the best performance and the most life from your expensive tubes! You can also measure the current draw of several tubes, to pick a set that draw similar amounts of current, electrically "matching" your own tubes! Works with 5881. 6550, 7027. 7581, 8417, 6V6, 6L6, 6CA7, EL34, KT66, KT88, KT90, and many, many more!
BiasTool mA (The Original)


BiasTool mV (For meters that do not read current directly)


DualBiasTool (Tests two tubes at one time, great for matching)


MiniBiasTool (For 9-pin Mini output tubes like EL84/6BQ5)


BiasTool PVT Octal (hands-free plate voltage tester)


BiasTool PVT Mini (hands-free plate voltage tester, 9-pin)



Click here to see the BiasTool PVT, the companion hands-free tester for a complete amp bias kit!



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