Upgrade PCB for Fender Blues Junior

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We repair a lot of Fender Blues Juniors.

One common problem is the pin 7 of the left hand EL84 valve shorting to the cathode via a PCB trace which has erroneously been run too close to pin 7.

We have thus designed a replacement PCB that avoids these faults. This is a high quality PCB: 1.6 mm FR4, 2 oz copper, plated through holes.

I've written a more detailed blog post about this with some pictures.

If any FB members want PCBs get in touch and I'll do you a better price than via eBay.


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Comments

  • ICBMICBM Frets: 39647
    That’s excellent. I’ve generally been able to repair the damage, but it’s not always easy and can look like a right mess, even if it works fine. A new PCB makes things easier and better. I’ve bought a couple of recycled ones from Rat Mods, but they’re not always available.

    The Fender factory bodge is ridiculous on a production amp. Given how many of them they’re making, surely it would be cheaper as well as better to redesign the board properly, once...

    Maybe you should licence yours to them :).

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • PhiltrePhiltre Frets: 1661
    Beautiful. But, as @ICBM says, it's incredible that Fender didn't use a redesigned board to the BJ 4 instead of bodging the old one. Why Fender, why?
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  • FunkfingersFunkfingers Frets: 4819
    It must be in homage to Leo. 

    The “Nocaster” guitar only exists because Leo Fender was too mean to waste the existing (i.e. already paid for) Broadcaster headstock decals. 

    Similarly, the contemporary company persists with its existing inventory of amplifier PCBs.
    Be seeing you.
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  • thermionicthermionic Frets: 5611
    Great work. Unbelievable that Fender, knowing of the problem, wouldn’t just redesign the pcb. 
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  • jpfampsjpfamps Frets: 1723

    The problem if you going to use a single sided board as in the Blues Junior is that the ribbon cable that connects the left-hand EL84 to the main PCB is laid out with the cathode connection on the right hand side, so the PCB trace has to pass through the pins on the right hand side of the valve socket.

    If the cathode connection was on the left hand side of the ribbon cable (as it is on the other EL84) then you could avoid running the PCB trace across the valve.

    However this would require that the main PCB is modified too.

    Having said that, Fender have already modified the main PCB once, so they could have sorted the valve PCB out at the same time.

    Alternatively they could have used a double-sided board for the valve PCB. This would have cost a bit more, but can't have been that expensive.

    Incidentally Fender have sorted out the oscillation in the MK IV Blues Junior by increasing the value of the snubber cap in the phase inverter to 470 pF. We use 220-270 pF here.
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