Fender Blues Junior FBJ (cream board) compatible replacement tube PCB with Bias Test Points by MOX

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MOX - Black Magic Amplifiers
Okehampton, United Kingdom
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About This Listing

Replacement PCB for Fender Blues Junior  - Fully Assembled

Fits FBJ 1, 2, 3 and 4 not suitable the very early version that has the wires for the power LED going to the tube PCB - search for "green board" version.

Beware of imitations! You can be assured this is the original and best FBJ board with bias test points. Others miss crucial features needed for best performance.

The original manufacturer's PCB is single sided, i.e. has copper on the non-component side only. The EL84 tubes run very hot in these and this weakens the glue that attaches the copper foil to the substrate material. The original substrate does not appear to be FR4 glass fibre but possibly an inferior composite such as SRPB. When the glue fails the heavy tube & socket is free to vibrate and soon the attached copper track fails due to metal fatigue. You hear crackly, popping and/or a loss of power When that happens the PCB needs replacement.

These replacement PCBs are designed to drop in and are made from a reinforced glass fibre substrate FR4. They also use a double sided copper foil with plated through holes. This overcomes the glue failure issue.


  • Fully assembled
  • Durable Glass fibre reinforced FR4 material
  • Prevents glue failure issues by using double sided PCB with plated through holes
  • Drop in replacement is cheaper and much easier to wire in than hand wired plate alternatives\Bias current measurement test points make tube replacement easier
  • Just unsolder the wires from the old PCB and attach to the new one.
  • No need to remove the main circuit board.Heatproof ceramic tube sockets
  • Much faster to upgrade than hand wired solutions as most of the wiring has been done for you
  • Better than uncertain hand-wiring as the location of 'wires' is fixed and pre-optimised for you giving repeatable results
  • Greatly eliminates the chance of expensive miswiring errors
  • Incorporates resistors for measurement of bias current on each EL84
  • Oversized holes to make re-wiring easier
  • Heater tracks optimized to reduce hum. No need for amateurish looking extra wires.
  • Instructions included. Anyone with decent soldering skills can do this.
  • Increase /preserve the value of your amp
Please note that these are not compatible with the very early 'green board" Juniors that have three resistors and two diodes on them. We have a different listing for those. We also offer a premium version with gold sockets and an adjustable bias mod kit.

Product Specs

ConditionBrand New (New)
Brand New items are sold by an authorized dealer or original builder and include all original packaging.learn more

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