Standby Switch for Blues Junior

By popular demand! People have been asking me for years for a standby switch on the Blues Junior, and here it is. I’ve seen a couple of implementations over the years, but they typically used an on-off-on switch with standby on one side and play on the other–kind of a kludge. Also, they involved cutting into the high-voltage wiring. I don’t like creating possible points of failure.


There isn’t room inside the chassis for another switch next to the power switch, even if you relocate the pilot light. Yes, you could cram a cheesy little switch in there, but we’re talking high voltage here, and only a heavy-duty switch will do. Fortunately, Carling, the same company that makes the power switch that’s in your Blues Junior, makes a clever progressive switch. It has three positions: off, standby, on–very logical. In standby, the high voltage supply is cut off. The filament and bias supplies receive power.

The kit is super-easy to install. There’s no soldering and–if you’re sensible enough to unplug the amp before you start–no danger. I supply everything you need: the switch, high-voltage wire, and a special connector, plus photo instructions. You can be back up and running in minutes.

Even though standby switches aren’t really necessary on low-powered amps, I’ve gotta say… it’s pretty cool! It’s a handy way to mute the amp when taking a break or when changing guitars. And even with the Billm cooler bias, the output tubes do run even cooler on standby.

The kits are available now. Order from the Mod Kits and Services page.

The kit does not work for the Pro Junior. The switch can be adapted, but requires removing the circuit board and doing some soldering.


  1. Tom says:

    Will this Standby Switch for Blues Junior work on a peavey classic 20 amp?

  2. Tom Levens says:

    I’ve come across a bit of information that might be of interest to your international readers. I’ve been repairing a cream-board Blues Junior sold in the UK that had been cooking it’s output tubes. Not only was the Bias set WAY too hot (as was expected) but the plate voltage was around 380V! The combination of the two was leading to the tubes dissipating about 16W at idle… toasty! In poking about, I noticed that Fender had the export transformer wired for 230V mains, but there was also a 240V option on the schematic. Thought I’d give it a try — it’s as simple as swapping the white/black wire connected to S2B (on the mains switch) with the black wire connected to P6 (on the main board next to the fuse F1). Now it’s running cool with a B+ of
    346V with the bias set correctly. If Fender are shipping all Blues Juniors to the UK (and Europe?) set for 230V, I’m guessing a lot of people might be running in to problems depending on their local
    voltage. So might be worth advising people to check their B+ and adjusting the transformer if necessary.

    • Tom Whitwell says:

      Tom, I just checked my UK Blues Junior, and it was wired for 230v. Not any more! Thanks for the tip!

    • Andy P says:

      This was true of my Hot Rod DeVille 212 as well! It’s being fixed by a friend at the moment and one of the first things we noticed when checking over the board was the incorrect voltage due to the connections to the transformer. Now it is running with a lower B+. This sounds like a common issue…

      • crsturmer says:

        Hi Tom, Thanks for this tip. To confirm, do you take the wire off S2B and put it on P6 and take the P6 wire and put it on S2B? Sorry, if I’m being simple, I just want to be extra sure before doing this!!

    • Lewis says:

      Just checked both my blues juniors and they were wired for 240Volts. I have now changed the wiring to 230Volts as you described.

  3. Don LeBlanc says:

    Would installing this Standby switch void the warranty on a Blues Jr … or are the changes easilly reversible ?

  4. mira arnaud says:

    Hello,I’m living in France and i will buy your standby switch. Do you give the schemat with it?

    Thank you

  5. Larry Seagle says:

    Will your standby switch for the BJ, work on my PRRI?

    • bill says:

      Yes it works. I’ve installed one, and it’s pretty cool. Unfortunately, I neglected to write down the lengths of the connecting wires, so I can’t offer it as a kit until I get another PRRI in hand and install another.

  6. Chris says:

    Would this by some chance also work Peavey Delta Blues?

    Thank you!

    • bill says:

      In theory, yes. In practice, you’d have to route the B+ supply to the switch and back to the board. Someone knowledgeable about the Delta Blues would have to do it. The connector I supply in the kit is specific to the Blues Junior.

  7. Javi says:

    This kit was super easy to install! You just have to take your time and be very careful when pushing/pulling the connectors onto the PCB. I braced the PCB with a finger while I did this. Works great, excellent work Bill!

  8. Mike says:

    Hi, will this standby switch work for Princeton Reverbs ? Thanks

  9. Mike says:

    Hello again,
    Will this switch fit / work in a blackface or silverface Princeton Reverb ? If so, how much is it and how can I order one ? Thanks again

    • bill says:

      It’s a very tight fit in a Princeton Reverb, at least in a reissue. I’m not offering it as a kit right now. The switches I stock have push-on connectors, so you’d have to install female connectors on the appropriate leads in the PR.

  10. Carlos says:


    I installed the switch while drinking a cup of coffee nursing a hangover on a Saturday morning! Easy to install and works great!

    Thanks Bill!

  11. Steve Adams says:

    Hi All
    To save any confusion thought would confirm officially voltage for UK changed from 240volt to 230volts(-6%,+10%) as of January 1st 2004

  12. Geoff says:

    Hi, The change of UK mains voltage from 240v to 230v is purely cosmetic. Nothing has actually changed, they’ve just shifted the error bands as shown in Steve’s post. It’s still effectively 240v, folks. 🙂 (This is to harmonise with the rest of Europe btw.)

  13. Love this switch…are the installation instructions on this site? We bought a few of them for the Lynda Kay band and I think someone else got my copy. Thanks can’t wait to have it in. -AM

    • bill says:

      The switch kit comes with instructions, 600V-rated jumper wire with insulated push-ons installed, and wire ties for putting it back together neatly.

  14. NHBluesMan says:

    is the middle position just not connected to anything?

    I’m interested in adding a switch like this to my Blackheart Handsome Devil, and i’m wondering if this would work on it. Thanks!

    • bill says:

      In the middle position, there’s power to the heaters and to the bias, no high voltage to the plates. Since the HD is cathode biased, you don’t have to worry about the bias. But you can wire it so that it interrupts the high voltage supply and leaves the filaments on.

  15. Neal says:

    I have the relic’d version of the Blues Jr and I’m wondering if my ‘aged’ nut and washer will work on the threads of this switch?

    • bill says:

      Yes, the nut will fit. On Relics, I also rough up the switch with sandpaper and/or a file and rub some black and brown permanent marker into the scratches to complete the rusty look. I do the same with the replacement input jack, which uses a different-sized nut than the original.

      Good luck getting the back and case screws out.

      • Neal says:

        ha, thanks Bill. I’ve already done your basic mods so getting in a second time won’t be a problem, it sounds amazing so far, I can’t wait to try the TO20 tranny I also ordered…

  16. CSCAN15 says:

    Hi Bill…want to get this and have a couple questions. With replacing the switch, do I have to worry about any voltage issues? Getting shocked? I thought it says “plug and play?” Shouldn’t you just have to unplug the existing terminals that are connected to the stock switch and plug them onto the new switch? Let me know.


  17. Naal says:

    Hey, Bill. You wouln’t happen to know if this switch works on a Vox AC4, would you? The little guy needs a standby for the sake of the tubes, and I can’t seem to find one here on the interwebs. Thanks!


    • bill says:

      No idea whether it would work on an AC4. Someone who works on them would be able to help. If it has the same toggle-type on-off switch, that would be a start.

  18. marko5702 says:

    Hey Bill just installed the stand by switch, I noticed a sight pop from the on to the standby position and even a louder pop from standby to the off position, is this normal?? Its quiet when flipping the switch the other way I have a cream board, does it matter which of the two white wires go to P9 or P10? Will you be making any white decals SB to stick next to the switch??
    Thinking about doing some of your other mods, what watt solder gun should I use. For the bias control is there a proper setting or is it by what sounds good to me? Thanks Mark.

    • bill says:

      Some noise is normal when switching in our out of standby. You’re switching AC, which goes from zero to full voltage to zero 120 times per second. If you happen to hit it at zero, you won’t hear a thing. If you hit it at full voltage you’ll hear a pop. In between the two extremes, you hear less. It’s nothing to worry about.

      Regarding the other kits, they come with full instructions, including setting the bias.

  19. lazarus909 says:

    Will this switch work with the super champ XD ? also what tubes would you recommend for the scxd? Thanks Bill

  20. TP says:

    Some words regarding the 230-240V issue: actually most of the time the main voltage I measure is near to 240V (speaking of Austria, but I think it’s the same in most european countries) I changed the transformer wires to 240 on my BJ a while ago to run it cooler, but my impression was: it sounds a lot softer and mushier with a noticable loss of clean headroom. The better idea is to leave it on 230V and set the bias cooler. High B+ voltage on a tube amp is a good thing.
    I always check the filament voltage on my customers BJ, if it’s the correct 6.3V or max 6.7V I leave the amp on 230V. Only if its much too high up to 3,8 or 3,9V it is better to change the transformer wiring to 240V

  21. Jazzman says:

    Got the switch in Friday afternoon. Followed your instructions, which wewre meticulously spelled out! My wife helped out. It took about 10 minutes and even Mr. All Thumbs had successfully installed the switch. I used the amp on tonight’s jazz trio gig and really enjoyed the new “standby” option the switch afforded me. It made a sweet amp even sweeter. I used it mainly as a jazz amp and it’s great! Thanks Bill!

  22. paulkearschner says:

    Ok, I bought a progressive three way Type Toggle Switch, to replace the on/off switch on my Peavey Classic 30, I’ve always heard and figured a standby switch is a good thing. I got this switch from Studio Sound Electronics, which by the way, is only a few miles from my house. Does anyone know if this can easily be installed on my Classic 30, or do I need to go pay a bunch of dough to have it done. Im kind of handy, but not real confident when it comes to amplifiers. Any feedback or tips would be greatly appreciated. Reply here or on my email, Thanks a bunch!

  23. Mark says:

    I may have overlooked this in the previous questions and comments, but will this work in an earlier USA Fender Pro Jr? Thanks!

  24. dominoe says:

    I had a repair shop in the Twin Cities install a stand by switch on my NOS Blues Jr., and now every so often the amp makes a horrible high pitched screeching sound. Never did this prior to the stand by switch being installed. Anyone have an explanation, it comes and goes, no volume up or down.

    • bill says:

      It’s possible that the switch is defective and that there is arcing on the high voltage side. It’s also possible that it’s just a coincidence, and that a tube is going bad.

  25. jhardikar says:

    Hi Bill. Just installed the standby switch as per instructions. Was pretty easy. Although… I am now noticing a hum/buzz that wasn’t there before. Not super loud but when plaing alone in a room it is definitely distracting. Specifically:

    1. When I put the amp on standby – there is a low hum – sounds like a low octave A# (with or without a guitar plugged in). This low hum is unaffected by Master or Volume controls.

    2. When I move to the On position – the low hum continues and now there is also a buzz – almost like its not grounded right. Not the same jarring buzz that you get when you accidentally plug in a cable into an amp and let the other end hanging loose, but definitely a buzz. This IS affected by volume, master as well as the clean boost.

    3. When I plug in my rig (guitar–>AC Booster pedal–>strymon reverb pedal–>BJr, even with both on true bypass, now there is a third noise – a very high pitched F# sound that almost sounds like what you hear when your ears ring. The hum and the buzz also continue.

    Nothing else has changed from before to after the switch swap.

    Thoughts on what it could be? I did clip the 2 wire ties to access the wires easier and then tied back the wires with the ties you provided (which was very thoughtful by the way!). Perhaps I tied them or placed the wires in a way that there is some interference?



    • bill says:

      Do you have an outlet tester? It’s possible that your outlet is wired backwards. Please check it.

      • jhardikar says:

        Hi Bill.

        I tested the outlet and the outlet seems to be wired correct. I thought it may be because it is a 2-prong ungrounded outlet (older home)… although the same outlet didnt cause any hum before the switch mod. So I took it to a friend’s house with brand new grounded 3-prong electrical wiring. Unfortunately I get the same symptoms 🙁

        Any other thoughts before I try and revert to the OEM on-off switch and see it it goes away?



  26. toppsseller says:

    Hi Bill,

    Will this standby switch work on a Blues Junior III?

  27. tjnugent says:

    Bill, will this standby switch work on the Excelsior?

  28. Wes says:

    Bill, thanks for this! My only primordial gripe (so far) in a new to me Blues Jr. III.
    Just ordered (you had me at “no solder”). Winters are long up here and, retired, days noodling around & wandering away from the amp while it cooks is not something I want to do. (Subjective but think tone suffers when sitting idle like that, then coming back after forgetting power-off many hours later & seems slightly muddier. Back to normal after some cooling.) Absence of standby switch should be a misdemeanor but price points are what they are I guess.

    Thanks again – looking forward to it.
    Be well sir!

  29. Willie B says:

    I just receieved my stand-by switch, voltage mod and present control, I’ve already put the stand-by switch in, and it works like a charm !! Thanks again

Leave a Reply

You must be logged in to post a comment.