Adding a Jewel Light

One of the dumbest things Fender did when they designed the Blues Junior and Pro Junior was to substitute a dinky little plastic lens for the traditional faceted jewel and #47 bulb. People have been asking me for years to install the jewel light assembly, and for years I’ve tried to talk them out of it, for several reasons.

First, you have to drill a humongous hole in the front panel. The extension that holds bulb socket barely fits over the circuit board. Next, it’s nearly impossible to tighten the nut that holds the threaded assembly unless you more or less gut the chassis so you can get in there.

The existing wiring won’t run the #47 bulb. It is designed to run an LED at reduced current and voltage. This is actually a good idea: less load on the power transformer, less heat. So you have to modify the bracket by cutting away the socket, shortening the arm, bending and drilling it, and installing support for a white LED. This assumes that you want a jewel other than red. If you want red, you can use the existing red LED, but you still have to modify the plastic “flower” that clips to the stock red lens.

I finally came up with a solution that is aesthetically and mechanically acceptable to me. I took my cue from the Series III Blues Junior, which has a non-removable red jewel and a red LED. Instead of the bulky ring around the non-removable lens with a thin nut on the back, I figured, why not thread the chassis and attach the lens directly? The resulting look is clean, minimalist, and doesn’t require a huge hole:

Click for larger image.

But that doesn’t mean it’s easy.

All of the lenses and holders I’d gotten from online vendors were metric, 14mm, super-fine thread. My first goal was to find a nut to fit them. Impossible.

I finally found a vendor, Antique Electronics, that sells jewels with an inch thread, 9/16″-24. I still couldn’t find a nut in that size, but I could at least buy an (expensive) tap in that size. To install it, though, is still tricky. I drilled the chassis with a 33/64″ bit, the right size to get proper thread engagement, and drilled the face plate to 9/16″, so the threads would not bind on the face plate, but the lens would seat against it. Then I tapped the chassis with with a 9/16″-24 tap. Don’t attempt any of this unless you have a drill press and a way to firmly clamp the chassis vertically. You also need to hold the tap solidly square to the faceplate as you cut the threads or you stand a good chance of  ruining the cut with an off-angle thread or a cross-threaded mess. Again, a drill press is ideal for this.

I removed the red LED from the “flower” and soldered a white LED to the leads. I trimmed the “petals” so the plastic would fit inside the lens. I secured it with a dab of hot melt glue.

Click for larger image.

Since this mod requires equipment that most folks don’t have, I’m offering it as a service for amps that come in for the Billm mods. There’s a waiting list for that, of course.


  1. Anthony says:

    This looks suspiciously like my amp, which you just modded and I received today! Thanks for coming up with the blue light for it — the color adds a whole new ambiance to the amp, and I really dig it. Not to mention the improved sound from the mods, of course! Thanks for the great work!

  2. roseblood11 says:

    I found an easier solution for my clone of the Catalinbread Formula No 5 Overdrive, and I think this should work fine for the Blues Jr as well. I used this cheap (1€) full asembly jewel light:
    One half of it can be used as a nut. A 10mm LED fits in there perfectly, I fixed it with epoxy resin adhesive, but hot glue will work as well.

    … I will try this in my Blues Jr soon. I replaced the cheap pots with better ones (with solder lugs and a mounting nut…), with cream chicken head knobs and a blue jewel light will definitely look great there…

    • bill says:

      I tried putting the jewel through the panel and putting the threaded housing on the back, but the panel and chassis were too thick and there were not enough threads to grab. It was easier to thread the chassis.

  3. Phil Connolly says:

    The plastic lens cover and little red LED is one of the few things I don’t like about this amp. I have thought about trying to figure out a change myself, but of course I want a traditional jewel and #47 bulb. So besides the physical space challenge you mention, there is the wiring.

    Looking at other amp schematics that use the T47 lamp, it seems like it is possible to wire one into the Bjr. Wouldn’t it be possible to (I have a green board) remove CR6, jumper R34, and then replace the LED with the bulb? #47’s run 6.3V 150mA, if that is adding too much of a load on the stock PT I suppose the new TP24 would do it.

    • bill says:

      The traditional jewel light assembly will hit the large filter capacitor. A 6V bulb puts more of a load on the PT, which is why Fender went with LED in the first place. You could mount just the threaded shell for the jewel and then position the stock red LED behind it. If you want a different color, you have to change the LED to white.

      • Rambler says:

        Hi Bill,
        For my BJ I ordered the entire jewel light and lamp assembly for $4.95 so I could get the nut to go with it and bought an LED light from Radio Shack. They make 3 different brightnesses so I got the largest one. I removed the stock LED from the board, drilled out the existing light hole (offset a little bit to avoid injury to the innards) and tossed the light bracket. I siliconed the LED into the light jewel and put it through the newly drilled chassis hole and secured it with the nut. Then I attached the LED wires back onto the board, observing polarity of course, cuz the only works in one direction. It’s worked like a charm for the last year.

  4. erlowther says:

    Bill, Along with other mods of yours, I’ve installed in my cream board blues junior, a new “green” Fender jewel light, which I now lit using a new white LED I purchased at Radio Shack, using the previous two wires from the original “red” LED light. Works and looks great! Thanks for the free info on how to do this mod.

    I have now installed your standby switch mod (which works perfect). As you know, in standby and “ON” position, the green jewel light is on (which is correct). However, there is room in the Fender jewel light’s cavity for another LED light to fit inside this single jewel light.

    My Question: Is it possible to separate the standby and “ON” LED power source tap on the cream board? I goal would be to….

    1. Use a single, clear Fender jewel light (with two LED’s inside) to indicate the mode. (standby or “ON”)
    2. Use a “red” LED to indicate the standby mode.
    3. Use a second additional “green” LED to indicate the “ON” position.

    Is this too much to ask in a mod?? Sincerely, ernie, Lexington, KY

    • bill says:

      It’s a good idea — I’ve thought about it many times. There are also dual-color LEDs, which would give you the ability to go from red to green or amber to red or amber to green. But it would also involve powering the LED from the high-voltage supply and reducing the power in some way. There’s always the possibility of component failure and the resulting delivery of high voltage to the pilot light area. While it might not cause a shock hazard, it could cause other damage to the amp.

      If I come up with a good way to do this, you can be sure that I’ll make it available as a mod.

      • erlowther says:

        Right, I figured you were on top of this troublesome high voltage issue. Perhaps adding a fuse between the pilot light and high voltage supply might be a thought. I believe the added benefits of a dual colored indicator light would be a nice feather in your cap to your already growing, well thought out, high quality mods. Keep up the great work. Thanks for the reply… ernie..

  5. tim2b98 says:

    Hi Bill,Is there a particular voltage LED I need if I want to switch to white? Also how much trouble is it to change the LED in the stock flower?

    • bill says:

      The 7000mcd LED that Radio Shack sells works fine. It’s in the 3 volt range.

      It’s fairly painstaking to work the LED out of the flower and put a new one in, but it can be done.

  6. cachedout says:

    I managed to find some 9/16-24 nuts for use with the jewel that Bill uses (from a coffee maker supply house). Shipping was crazy so I got 5 nuts instead of 1. Anyway, I’ve found this site to be so helpful, I’ll send those 4 extra nuts to any four people who are going to use the Antique Electronics jewel. Peace.

    • tdunn2 says:

      hey todd I am trying to do this on my relic. I would be interested in one of your left over nuts if you still have em to spare. thanks Tim

    • Dallas Stevens says:


      I’d be interested in one of your spare nuts. be happy to PPG you a couple of bucks… let me know.

      dallasstevens3 (at)

  7. ejacoby says:

    Bill, Just checking in to report on one of your Blues Juniors. I bought an almost totally modded tweed in 06 and brought it to your house for the prescence control which you were kind enough to do while i waitied. Ive since added the standby switch and have been using it weekly for the past 3 years in a pretty loud jam thing. Ive gotten many admiring comments about what a great sounding amp. One of the comments coming from a guy with a Carr. Its been totally reliable,pretty ballsy and sounds great clean as well. Thanks for such a great improvement. One question. Any chance of you getting involved with modding the Princeton??

    Thanks again, what an amp.

    Elliot Jacoby

    • bill says:

      The Princeton Reverb doesn’t need much improvement in my book. I do a little power supply stiffening and upgrade the output transformer. That’s it.