Questions and Answers
I get lots of questions from folks who want to modify their Blues Juniors. You’ll find most of the answers on the Mods in Detail pages. I’ve added some questions that I’ve gotten via email, along with the answers. You can post additional questions here.
hi bill whats your experience with the thd yellow jacket yj20d used on the bj which has been converted to 6v6?
No experience. Seems silly to me.
Hi!
My idea is that I would want longer reverb for my n.o.s. tweed (year 1995) blues junior…”something” than older or a bigger fender amps. I think ,that now in there is some short reverb unit (accutronics). Can you recommend some longer reverb unit? What you think, is it modification healthy when it is changed?
The long reverb tanks don’t fit in the Blues Junior. The 8EB2C1B or 3EB2C1B tanks available from Ruby, MOD, or Belton all have longer, slower delay than the Accutronics tank.
You could hacksaw the ends off a long tank from a Blues Deluxe or Hot Rod Deluxe, but it’s a lot of work.
Ok. I nearly like blues junior reverb “then” than I play (single-coil) guitar with bridge pickup and very nearly on the bridge place…”then sound” is very nearly perfect (surf sound??). What you recommend for me?
If you want more delay or deeper reverb, get the Belton or MOD reverb tank.
Hi Bill,
I saw the comments above about pine cab replacements for the Blues Jr. I’ve got some Red Oak that’s been drying for about a year and a half (Originally going to be a few other projects, but I’m putting those off). Do you think the Hardwood would make a difference in the tone? I’m sure that the pine being a softer wood is going to deaden some of the tones produced by the speaker.
Overall, the wood has very little effect on the tone. Just about every other mod has more impact. After all, it’s an open-backed cab, so the sides (you can pretty much discount radiation or absorption from the top and bottom) don’t really get all that involved. And you can argue it both ways: A dead, heavy, MDF cab keeps all the energy in the speaker and lets it perform most efficiently. A light resonant wood may add some of its own tones, but in order to do that, it has to steal energy from the speaker. And once you apply tolex or tweed, the characteristics change again.
But people hear what they want to hear, so whatever cab material you choose is fine.
Hi Bill,
I installed the following modifications, Cream Board Basic Kit, TO20 Heyboer transformer,Switchcraft input jack,Aux speaker jack,Standby switch, and Line out jack.
Everything seems to be working fine and the amp sounds really great. I did notice that it seems to be running hotter then it used to, is this normal or could I have screwed something up? (bias voltage set at 3.5 as recommended for EL84′s)
Thanks
Rich
There’s no reason why the amp should be running hotter. If anything, it should run a little cooler. Maybe you’re just playing it more!
I have a problem with my blues junior. When I start the amp and play at anything BUT the power tubes cranked the amp runs fine. However, when I crank the power tubes louder I start to get this buzzing overtone that sounds horrible on any note I play on the guitar. I have tried a different guitar, checked my wires and pedals, and replaced both the pre amp and the power tubes.
Any help?
Sounds like phase inverter oscillation to me. See here:
http://billmaudio.com/wp/?page_id=115
I have a blues junior that I play my harp through. (Treble off, Mid off, bass on full, master volume full, no reverb and overdrive button on with volume about 3-4. Not a bad sound but not the wailing sound of the Fender Champ.) I had to get the BJ repaired as it stopped working. I asked a buddy if I could borrow his 1956 fender champ. (Stock) It is magnificent for blues harp! Trouble is he will not sell it to me. Any ideas as to how I could tweak my BJ to sound a bit like the champ? Kindest reagrds, Larrie Cook. http://www.larriecook.com
I’ve done a “thickness control” mod on some Blues Juniors for harp. Harp players say it works very well. It’s not a kit; I’d have to think about whether it could be. Like the presence control, it involves drilling a hole in the top panel for a pot.
Bill, did you ever complete that head project you started back on the old site? How did it turn out? What did you do with the reverb?
Still not done! Too many customer amps to mod.
Hi Bill,
I’ve just got a Blues junior off ebay, and I’m gonna try some of your mods. The amp’s fairly new so I assume its a cream board. However, I noticed that when i let notes sustain (especially bass notes or chords) a second or two after the initial note attack i get a gurgly distortion/buzzing sound creaping into the sound, which gets louder, and is irritatingly audible as the notes fade away. Any idea what this could be? I want to sort it out before I start modding. Also the reverb doesn’t quite turn off when the control is on 0, its always there in the background.
Thanks,
Luke
It’s phase inverter oscillation.
See here: http://billmaudio.com/wp/?page_id=115
Thanks, you were right, the blue wire from the OT was touching one of the output valve ribbons, as soon as I moved it the noise disappeared! Is it usual for the reverb not to turn completely off with the control on minimum? I may install a switch, as I’m not used to having an amp with reverb!
Regards,
Luke
Sometimes a little reverb sneaks through, even if the control is off. It may not be the pot; sometimes there’s crosstalk into the reverb circuit. If you want reverb on/off switching with a footpedal, you can install a mono 1/4 inch jack in the reverb tank (tight fit), wire it so it shorts the output (black) side to ground, and run a guitar cable to an on/off footswitch. Keep the cable short so you don’t get hum.
Bill, Looking at the schematic would that be shorting P3 to P4 for the reverb switch?
Thanks, Kevin
What?! NO! P3 is the output transformer and P4 is the hot side of the AC!! Disaster!
You mount a mono jack IN THE REVERB TANK. Connect the center pin of the output side of the tank to the center pin of the the mono jack.
Bill,
I recently purchased you entire mod kit. Since I have no knowledge of working electronics I asked a friend to put the mods on my amp. He is close to finishing them, but says the instructions for installing the the auxiliary speaker jack kit and the line out jack kit are not very specific. He says there are picture, but there isn’t any instructions to tell him where to solder the wires for these two kits. I looked over this web site to see if I could find such information, but I too am stumped. Can you help me out on this? Thanks
Bill
The photo shows that the green goes to green and the black goes to black. I don’t understand the mystery.
Hi Bill
I just ordered some mods from you that a friend will be helping me do. And we’re looking for a schematic for the Blues Jr and am wondering if they one available on the Fender site support page (http://support.fender.com/schematics/guitar_amplifiers/Blues_Junior_Schematic.pdf) is for the GREEN or the CREAM board. Can you tell me?
Best wishes
Richard
Both schematics are in the same PDF. Check the dates in the box in the corner.
I should have specified what rev. schematic I was refering to. On the green board P3 and P4 are for reverb. Thanks for the info.
Hi Bill!
I modded my Blus Jr. with a kit that practically is the same as the basic kit of yours only with a fixed bias. Being that said, can I install the TO20 output transformer? Thanks.
Yes.
Hey Bill,
Just wondering if you can give an outline of what mods you did for the Stevie Snacks guys amp. My amp has a green board (1997), and I want those mods…Also, I’ve recently moved to Australia and need to convert my amp to 240 instead of bothering with a step downs. Will this affect any of the mods spoken of and does the Power and Output Transformers and Chokes that you suggest come in this voltage?
Cheers
Anthony’s amp has the basic mods, TwinStack, presence control, cathode follower, and TO20 output transformer. His was also the first to receive the larger coupling caps, which are now part of the basic mods. I think I also installed the Switchcraft input jack and standby switch, but don’t recall for sure.