adjustable fixed-bias

 

Adjustable fixed-bias and cathode-bias for the valve junior

    I know, “adjustable fixed bias” sounds like an oxymoron and is usually not associated with small single-ended amplifiers.  It’s true though, you can have adjustable fixed bias for the Valve Junior.  It just depends on what version of Valve Junior you have.


    Through the evolution of the VJR, Version 1 is the worst.  Version 2 offered some improvements, but was still lacking in design.  Then Version 3 came along with some significant improvements.  Unfortunately,  with these improvements Epiphone also did away with the little known and under utilized secondary tap on the power transformer.  This gem of an asset can open a whole slew of opportunities for the Valve Junior lucky enough to have it, adjustable fixed bias is one of them.


    There are benefits to both adjustable-fixed bias and cathode-bias as you can see to the right.  Typically, an amplifier is configured with one or the other bias schemes.  So, wouldn’t it be nice if you could have your VJR outfitted with both?  Well, you can...with a flip of a switch.  It’s really that easy and instantaneous.  Some potential applications for these settings would be: fixed-bias for rhythm parts with a tight bottom-end and better headroom.  Flick the switch to cathode-bias for blues and rock solos for better compression and sustain. Whatever your playing style is, this modification certainly offers a good deal of flexibility.   


    So, if you have a version 1 or 2 you are very much in luck.  Actually, if you have a spare version 1 or 2 power transformer you are equally in luck.  The irony here is, for less than stellar versions, they do offer some hidden treasure.  Adjustable fixed bias control only scratches the surface.  Please e-mail: b5amps@me.com for more information and check out our Price List for pricing.


Fixed-Bias Advantages:


  1. More headroom

  2. More output power/wattage

  3. Tight and punchy bass response

  4. Precise control of EL-84 quiescent current. Meaning, the ability to fine tune and find the “sweet spot” operating point of the EL-84 power tube

  5. Bias the EL-84 hot or cold and anywhere in between without having to unsolder and swap out any components



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Cathode-Bias Advantages:


  1. Touch-responsive

  2. Better compression

  3. Liquid and loose feel