If you're a musician, you'll appreciate the sound of a properly biased tube amp.  Your wallet will appreciate the longer life you can get from your output tubes.  Our bias tools are easy to use, and provides a fast and accurate way to get the best sound from of your amp. Matched output tubes and proper bias are the ingredients to quality sound and longer tube life.   

A bias probe is inserted between an output tube and the amplifier. It monitors the total current flowing through the tube. Current is read on a digital voltmeter (DVM) and may then be easily adjusted to the required settings.


   
 TUBE BIAS CALCULATOR (for push pull class AB1/AB2)

Tube Type

Plate Voltage

Power W

Plate Current mA
+/-10%
Cathode Current mA
+/- 10%
- - -


 

Eurotubes™ Bias Probe
For 8-pin power tubes such as 6L6, 5881, 6550, 6V6, EL34, etc.   Requires separate digital volt-ohmmeter capable of reading current.   This device reads cathode current, but not plate voltage. 

Not a kit - this device is fully assembled and ready to use!

Complete with detailed instructions.   Used with a basic multimeter (Get Yours Here).  Note: this adapter, as designed, will NOT test 7591 tubes.  
Part #EBP-1

$34.99



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Revisit™ Bias Checker Kit by Hoffman Amps The Revisit Bias Checker Kit by Hoffman Amps is the best of both worlds when it comes to ease of assembly and cost effectiveness. This kit is easy to build, and comes with assembly instructions in the link below. 

Kit builds one bias probe to be used with a multimeter. 
(Get Yours Here).

Download assembly manual here.   Requires assembly.  Soldering capability and tools required.

KIT ASSEMBLY DIFFICULTY:

For 8-pin power tubes such as 6L6, 5881, 6550, 6V6, EL34, etc.   Requires separate digital volt-ohmmeter capable of reading current.   This device reads cathode current, but not plate voltage.   Used with a basic multimeter (Get Yours Here).  Note: this adapter, as designed, will NOT test 7591 tubes.  

Part #HABK-100

$24.95


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COMPACT DIGITAL MULTIMETER.  Compact, reliable, inexpensive.  Dimensions:  5-3/4" L x 2-7/8" W x 1-1/2" H
 
  • LCD backlit for low light situations
  • Rubber outer case makes it shock resistant
  • Flip out stand for workbench testing
  • Continuity tone for blind testing
  • Right angle banana jack test leads save space
  • DC Voltage: 200mV/2V/20V/200V/600V 
  • AC Voltage: 200mV/2V/20V/200V/600V
  • DC Current: 200uA/2mA/20mA/200mA/2A/10A 
  • Resistance: 200/2K/20K/200K/2M/20M Ohm 
  • 3-1/2 digit, 1999 count display measures AC/DC voltage, DC current, ohms and diode/transistor check.   Works well with our bias probes, and for general trouble-shooting.  Backlit LCD display, easy-to-read 1/2" high digits,
    Includes test leads, standard 9V battery and owners manual. 
    Part #A830L

    $22.95

    Compatibility

    The Eurotubes™ Bias Probe™ and the Revisit/Hoffman Bias Checker may be used with any amplifier that provides for adjustable bias and uses 8-pin power tubes with the cathode connection on pin 8, including:

    EL-34 KT-66 KT-77 KT-88
    6CA7 6L6 6V6 5881
      6550    

     

    Note:  Some amplifiers offer adjustable bias, and some do not.   Bias adapters will properly measure the cathode current on most all amplifiers, even if they do not offer a bias settings (certain Music Man amps are an exception).  You may wish to have certain fixed bias amps (such as Mesa Boogie™) modified by a technician to provide for bias adjustment.  Vintage blackface Fender™ amps from the 1960's offer true bias adjustment.    Silverface Fender™s from the Fender™ CBS era offer a bias balance  control, which balances the bias between the output tubes, but doesn't really offer  full bias adjustment.    Most Marshall™ amps with 8-pin output tubes offered adjustable bias up through the 1990's.    For other brands of amplifiers, refer to the manufacturer's literature and specifications to see if the bias is adjustable.