TO20 Low-Profile Output Transformer
This brilliant new output transformer, co-developed with Allen Amps’ David Allen, is a breakthrough for the Blues Junior, Pro Junior, Princeton Reverb Reissue, and Super Champ XD. Designed from the ground up to provide big-transformer performance in the least possible space, the TO20 is built by highly respected US manufacturer Heyboer, fits the stock mounting holes in all of these amps and has the same height as the stock transformer. The “widebody” core is made of premium M6 steel, which has superior magnetic properties, allowing maximum efficiency and power transfer from primary to secondary.
Princeton Reverb, TO20, Blues Junior/Pro Junior output transformers
At 1.5 lb., the TO20 is more than half a pound heavier than the stock transformer for any of the above amps. The core size is carefully balanced against the wire gauge and turns ratios. The design increases the “Q” of the output circuit and provides a higher damping factor. The amp thus controls the speaker more accurately, which is especially beneficial for low frequencies. Flaws like woofy, flabby or farty tone are a thing of the past. Overdrive tones are sweeter, harmonics are richer. Frequency response extends well past the range of hearing, so nothing is left behind.
Output transformers seldom make an amp louder; they’re mostly about tone quality. But they do improve headroom by reducing distortion.
Below is a power spectrum sweep, using a stock Blues Junior OT:
Power Spectrum, stock Blues Junior OT
Next is the same sweep, same amplifier, nothing changed but the OT:
Power Spectrum TO20 M6 core
You can see that the power curve has shifted up several dB; the increase in loudness is just noticeable, not overwhelming. The real difference is in the distortion-free bass and improved tone throughout the range.
The only “caution” is for Princeton Reverb users, who may like the classic grind of the stock, undersized output transformer, what Fender’s Shane Nicholas calls the “aaaaaat!” tone. But it’s the same tone that forces you turn down the bass as you turn up the volume. With the new OT, the bass comes through in a way that you’ve never heard—unless you’re one of the old-timers who tore out the stock PR OT and installed a Deluxe Reverb OT. The TO20 gives you all of the performance of the DRRI transformer or other oversized aftermarket transformers without having to drill holes, find and attach the right quick connects, or worry about interference with speakers. (The “20” designation is just to differentiate it from the TO22; either OT can easily handle 25 watts.)
The Billm TO20 kits fit the Blues Junior, Princeton Reverb, Pro Junior, and Super Champ XD (SCXD available end of October), with the correct wire lengths and the proper push-on quick connects for each amp.
For reference, here is the power spectrum for the TO22 transformer, which has a 4 ohm tap as well as an 8 ohm, and is preferable for maximum efficiency running two speakers or a 4 ohm cabinet. You can see that the TO22 is very similar to the TO20, and both are superior to the stock OT:
Power Spectrum, TO22
You can order either output transformer from the Mod Kits and Services page.
Hi Bill.
I’m absolutely loving my Fender PRRI with your new OT and JJ 6V6 tubes. While you were doing the mods I had ordered a Weber 10F150T ceramic speaker, no dope, to see how sweet a tone I could get in addition to your mods.
I had read in various forums that the stock Jensen was a very weak performer, responsible for flabby, farty bass. Now I know that is not so. I heard the stock speaker after your mods and really loved it. Then I received the Weber and thought things would get even better. Well, I didn’t have the 10F150T in the PRRI for more than a week. After putting it through many paces, I re-installed the stock Jensen. To my ears, the Weber changed the tone, but not in a Fendery way. Now, the stock Jensen tone reminds me of an expensive, sweet acoustic guitar with a low, rich bottom end–without the boominess of overblown bass on the 4th string E note and an anemic 6th string E, which I do not like at all. Now, the 6th string E is the solid bass foundation, with pants-shaking muscle and no flabbiness.
I must indicate that I do not play gigs. I am a living room player and the volume control hovers at around 4 or below, unless it’s a weekend or the landscaper is cutting the lawn. This amp has balls. For OD I use a Keeley-modded Ibanez TubeScreamer with True Bypass–I don’t want any circuitry getting in the way of the killer tone when clean. With the new OT, JJ 6V6s and stock Jensen, I cannot think of any way to improve the PRRI. Seriously.
Thanks again!
Bill
hi..i love to really pound on my heavy e string on the neck position..i tune to e-flat….but always have to back off because of flbby woofy sound…what will the TO20 or TO22 or even TO26 do for my problem?
cheers thanks mike
The TO20 and the basic mods will be a revelation. The BJr can deliver solid, authoritative bass… or as much as you can expect from a 15-watt amp! At any rate, it’s a huge improvement.
Bill,
Been considering what to do with my Jr. after I have installed a Weber 12A125 and all new (old) tubes. I am building a new cabinet just for fun and because I have the means just to see what it sounds like. I know Fender made a “Two Tone” amp with a 12″ and a 10″. I have an extra Eminence 10″ and was thinking about building a cabinet for both speakers. I also have an extra Weber and the original Fender 12″. What would I need to mod to run either the 12 and 10 together or two 12′s (separate cabs)?
Thanks for having a very informative site!
Martin
The Two-Tone was a not a big seller, but it used a 12 and 10 in one large cab, with the BJr chassis offset to one side. They used the stock transformer to drive a 4 ohm load. I’ve upgraded a couple of these with the TO22 transformer, using the 4 ohm tap, and it sounds noticeably better. The TO20 transformer has lots of iron too, and can drive 4 ohms without difficulty, despite the slight efficiency loss. Adding an aux jack will make the job of driving a second speaker easier. You should have power supply stiffening (part of the basic mods) to give the output tubes all the current they need to move a couple of cones.
Here’s a pic of the Two-Tone. The guitar leaning against it gives you an idea of how big it is.
If I were to buy this OT, can you tell me if there is a difference in bias if we have the stock OT, assuming we’ve done all your mods?
By the way, I’ve done ALL of your mods to my BJR, and I love them. Thanks for making it so easy!
Yes, you get a different bias reading, but I provide the new values. If you use the same tubes, you may not have to touch the bias trimpot.
I was at a local guitar shop and they were pushing the Mercury Magnetics OT for my BJr. Is there a difference between Allen OT and the Mercury magentics version?
Thank you
In my experience, Mercury Magnetics makes very good, but premium-priced products. I’ve worked with the MM output transformer for the Blues Junior, and was not impressed. It’s open frame, without bell ends, like the stock OT, has lower primary resistance, which means less wire inside, and is not particularly beefy. It sounded a little better than stock, but not as good as the TO22 or TO20. The TO20 is really in a class by itself, specifically engineered for the Blues Junior, but coincidentally a perfect solution for the Princeton Reverb and Super Champ XD. The TO20 greatly increases the output circuit’s damping factor, the accuracy with which it controls the speaker. There’s only one way to improve this: a heavy core with lots of wire.
You need the basic mods, especially the power supply stiffening, to get the most out of any upgrade output transformer.
Dumb question but here goes…Is it neccesary to remove the PCB to install the TO20 in the Super Champ XD? I hear removing the board from the SCXD is quite a bit more difficult than the BJr. Thank you
It is not necessary to remove the circuit board in the SCXD to replace the OT. And a good thing–it’s a bear to remove!
bill,i wanna buy a to20 transformer and install it in my n.o.s. jr. how easy is it to install for an amature ,and will it make a noticable improvement w/out any other mods?
You’ll hear some improvement with the TO20 transformer, but you’d hear more if you did the basic mods–the power supply stiffening helps you get the most out of any transformer upgrade. And while you’re in there, it makes sense to do the tone stack and adjustable bias too.
Im considering your TO20 for my PRRI,but in your info section you said “Choose this transformer if you dont need an aux speaker jack…”. This may sound like a stupid question, but how will this affect the aux jack I already have in my PRRI?
The reference to the aux speaker jack is for Blues Juniors, not PRRIs. The TO20 works fine in the PRRI whether you use the aux jack or not.
Hi Bill,
Well, I got the T020 OT but decided to take it to a tech after an initial attempt to do it myself. I have a greenboard US version and was intimidated when it came to removing the circuit board. The improvement is very huge. My bandmate has a MIM BJr but always uses an effects unit so I had not heard his amp straight up. I wish I had borrowed his sooner after making the previous adj bias, tone mods and reverb mods, JJ power tubes and Hellatone 16ohm speaker. The A/B comparison after installing T020 was absolutely stunning – night & day – 2 completely different amps. The stock amp was terribly boxy, poor bass response and somewhat lifeless. Mine sounded HUGE, great bottom, beautiful articulation across the spectrum and about 25% louder, even with the 16 ohm. I could not be more pleased – amazed actually. I will soon borrow my bandmates Deluxe Reverb R/I and I expect my BJr to give it a good run for the money. I got my BJr used and guess I have about $525 invested – still less than the way inferior stock amp. I’ll do a follow-up after the DRRI A/B. Thanks mucho again! PEACE, Richard
What is the primary impedance of this new TO 20 transformer Bill ?
8K ??
The impedance is 6,600 ohms.
Hi Bill,
Thanks Bill.
How come so low? I thought Princeton Reverb OT’s were targeted at 8k primary impedance? 6.6K sounds more like a Deluxe reverb OT Primary impedance.
How will the different impedance affect the tone or performance of the Princeton reverb?
An aside, I have always wondered why a deluxe reverb has an OT with ~ 6K primary, whereas the Princeton reverb (that also uses two similarly biased 6V6 output tubes) used 8k as its primary impedance.
You can pull a couple of more watts out of the tube with a little less impedance. Back in the 1960s, people were putting Deluxe Reverb OTs into Princeton Reverbs for better performance and tone. The whole point of the TO20 is to get Deluxe Reverb OT performance in a bolt-in size for the PR.
Hi Bill,
After finding your site I recently installed the T020 OT in a PRRI. Everything else in the amp is stock. Do you know if the amp will now be able to run 6L6s (after rebias) or are there other components/values that would mean trying this would be a mistake?
Thanks.
6L6s run considerably more filament current. It’ll cause your power transformer to run pretty darn hot. Try JJ 6V6-S tubes. Their plates are nearly the size of 6L6s, but they draw less filament power.
Hi Bill,
I play harp and have your mods on my Blues Jr.(Cream Board). Will a T020 transformer work well for distorted blues harp sound?
Thanks’
Roger H.
The TO20 will give you richer lows and better sound quality, maybe not what you’re looking for in a harp amp!
I just purchased a BJr for the first time. After reading through your site I decided to purchase the basic mod. Is this the right place to start? I am not gigging at this time but who knows? Just want to make sure I get this right.
Thanks
The basic mods are always the best starting point–that’s why they’re the basic mods! Definitely the most bang for the buck.
Hi Bill,
What kind of change can be expected for a SuperChamp XD with this transformer. I had read your other info on the XD and it seemed you had come to the conclusion that apart from tubes and speaker swaps, there weren’t mods that were worth the effort involved, i.e, the Op amps.
Is the swap to this OT a “plug and play” type operation?
Thanks!
Phil
The transformer swap is plug and play, but you should check the bias when you’re done. The OT gives a fuller, rounder sound, especially in the bass. Coupled with JJ 6V6s, it sounds very nice in the SCXD. The JJs like hotter bias than the stock tubes. I run mine at 50mV instead of 40mV.
I just want to join the chorus on how great the TO2O plus the basic mods are. My green board BJr is a finally after 12 years, a really great “Fender sounding” Fender amp. Fuller, deeper, richer, more dimensions to the sound … more clean, more touch response, more smooth clipping — and when cranked up, a lot more “party,” with real tone and nuance control — sounds better than any PR I’ve heard, covers the tweed gamut, and seems to go further, say almost into Dumble territory. And with Bill’s clear directions, the mods are actually fun to do for an afternoon or two.
Let me make sure I understand. I would like to install a T020 into my Superchamp XD. Is this a plug-in mod, or will I have to be soldering to a PC board? (Never done that). Thanks in advance.
There’s no soldering to the board. The OT plugs in and the leads are color-coded.
Hi Bill,
I just installed the basic kit for the cream board and everything turned out great! I’m looking into purchasing and installing the TO20. In terms of difficulty, how would you rate the installation of the transformer compared to the basic kit?
The transformer is plug and play, but you have to partially remove the circuit board again, or get it loose enough to run the black and green wires from the chassis hole to the speaker jack.
i just did some mods including this and i cant believe it. This is probably the best sounding amp ive ever owned. Next on the list is those octal sockets
Hi Bill, I’m just in the process of installing the transformer but I’m afraid I didn’t note the order in which the green and black wire were on the jack daughterboard – green at the front when facing the back of the amp or black? It isn’t noted in your printed instructions. Does this matter at all – I don’t to stuff everything up.
Thanks
ok, I’ve just spotted GRN (front) and BLK (rear) on the PCB – must get my eyes checked. Have to say that the mods I’ve done so far, the basic kit and presence control etc have really transformed the amp into something I’m REALLY enjoying playing. Cheers.
hi,
will the to20 fit/work on a pro jr.?
do you have a 220volt (eu voltage) model for that amp?
thanks.
The TO20 works well in a Pro Junior. There’s no difference between 120/220V operation for the output transformer. The power transformer takes care of the voltage conversion; all of the other electronics in the amp are the same, regardless of the mains voltage.
My blues jr’s low end seems to be very “overwhelming”. However, if I turn down the bass, it sounds really thin. I think this is called the bass being too “loose”? Should I invest on an output transformer?
Have you done the basic mods? The BJr’s stock tone is very unstructured and the tone controls interact heavily. I think it’s essential to get the electronics and basic tone squared away before giving it a “premium” sound with a better output transformer.
Bill,
About 1-1/2yrs ago I bought all of your mods and had them installed by a reputable tech. I loved the mods and it was a great improvement. Now here is the dumb question. Was the OT in the older mods different than the T020 Low-profile or are they the same only the newer version is-low profile? Thanks, John
The older output transformer, the TO22, is still available. It has 4- and 8-ohm windings, while the TO20 is lower and wider, with only an 8 ohm winding. They sound pretty much the same. Our goal was to get TO22 performance in a size that wouldn’t hit larger speakers in the BJr cab.
Bill,
I just have to thank you for your amazing customer service.
After ordering the wrong OT you had no problem sending me the right one and answering all of my questions.
I installed the OT in my Corona Cali Blues JR and, to me, the tone is outstanding. Everything just seems cleaner and crisper. It allows me to crank the preamp volume and get that real overdriven sound without it getting all muddy. Works great with my tele and les paul and makes all my pedals sound better.
I would recommend this inexpensive alteration to anyone with a Blues JR.
Thanks again,
Justis
Hi Bill,
Just got the TO20′s in and installed one into my old green board and my newer cream board BJ’s. This combined with your other mods have made these two amps sing. I have a stock tweed reissue that I’m using as a refference for what the amps used to sound like and I can’t believe the difference. Thanks for all your hard work on making these amps the best stereo rig I’ve ever owned!
Hey, I believe my power transformer is done. I recently noticed smoke was emitting from power transformer, so i disconnected it and have been researching for a trannie with a little more head room to keep the amount of heat at a minimum. Do you have any recommendations?
The replacement power transformer from Mojo Musical Supply is an exact fit, but has a little more core. It runs cooler. I like it.
Hi Bill
If I purchase a USA blues junior is it an easy job for me to swap out the power transformer so I can use the amp in the UK?
If so what power transformer would you recomend for the job? I don’t need an upgrade just a standard replacement.
Thanks
Shay
It’s not difficult to change the power transformer, but it is hard to find it. Connecting the jumper wires properly for 230 or 240V can be a little confusing, but the schematic has a diagram. You may be able to get the Fender transformer from a dealer in the UK. The only non-dealer source I know of for the transformer outside of the dealer network is Tube Amp Doctor, in Germany.
Wow, that was the last piece of the tone puzzle! The mud is gone, and there’s a sparkle and clarity the amp never had before, not to mention a much better defined bottom end! This baby’s got back!
Is this OT suitable for a Silverface Princeton Reverb? An easy solder job I’m assuming?
Thanks!
Nick
Yes, it’s a drop-in for any Princeton. The color codes on the wires are the same.
Just did this mod too. Sounds great. Farty bass is gone! Sounds like a boutique amp!
I’m presently moving my Super Champ XD chassis to a larger cabinet to accommodate a 12″ speaker. It is a Jensen C12r if it matters… It is a 16 ohm speaker which leads to my question. I’ve considered two options. Option one – add a 15 ohm, 25 watt, cement type wirewound resistor wired in parallel with the speaker (dropping it to roughly 8 ohms). Option two – just live with the mis-match and hope for the best as the speaker jack states “8 ohm minimum” and I seem to recall seeing you state on another thread somewhere that the SCXD will take the 16 ohm load no problem.
I’d love to know two specific things from you if possible:
1) What option above would you suggest and why? (How would it change tone/volume if at all… fyi – I DON’T want more volume as a default – just the best possible tone)
2) I’m intending to upgrade to this TO2O transformer in the near future – does that change your answer at all?
Thanks in advance for your help!
Trying to match impedance with a resistor is a waste of time and a waste of power. You’d be better off living with the mismatch and MUCH better off getting a better speaker with the right impedance. I have a poor opinion of the 12″ R cones, although the C is much better than the P12R.
A few users have experienced oscillation problems with the TO20 in the SCXD. I’m not recommending that application until I research it further.
Thanks for the quick answer! Seems like everybody loves the Ragin Cajun in the SCXD but I’m not a fan – at all… I don’t want more volume as the amp “stock” is just the right volume. A louder speaker means I’d need to bring my attenuator which brings the “convenience” factor and tone quality down a few notches… I love the tone of the old Princetons amps hence the Jensen C12r speaker… I could purchase a C10r in 8 ohms if you think that would work better – I’ve just always preferred 12” speakers over 10”s as a blanket statement (personal preference obviously). On the eminence website – the 10” Legend 1058 sounds way better to my ears than the RC… Any other thoughts or direction on that?
I’ll also be eager to hear what output transformer you do suggest as I hear that can make a huge difference in an amp… You are wonderful to deal with and I’ll absolutely be purchasing your products in the future…
A louder speaker means I’d need to bring my attenuator which brings the “convenience” factor and tone quality down a few notches…
Since the SCXD has both volume and gain controls, I can generally find my tone at most any loudness level.
The C10R sounds really great in a Princeton Reverb; no idea how it would work in a SCXD. I like the 1058 too–a classic speaker. Any uncolored 12 would work well.
I’m sure that the TO22 would do a good job in the SCXD. You’d have to drill a new hole for one side of it; make sure you use a drill stop so you don’t hit the circuit board!
Bill,
Is the TO20 transformer available for the Super Champ XD? If so do you supply all parts and instructions for the mod?
Thanks, Robert
A couple of users have reported oscillation with the SCXD, but many others love it. I’m holding off until I do more research.
Hi Bill ,what’s the status of this?
I have a new SCXD that I’m planning gigging with, and to that end I’m looking for improved low end and as much additional volume as I can get semi-easily. Will your TO22 OT upgrade and JJ 6V6S’s biased at 50mv add both bottom and level? I’ll also be adding an Emi 1058 or Copperhead most likely as well.
One mod that does help is the addition of Line In to create an FX Loop, so for now I’ve got an EQ in it that’s adding bottom and a little level (MXR 10-Band).
Thanks for any advice etc!
Doug
The upgraded OT will be slightly louder, but it’s mostly improvement in tone quality and extended bass performance.
hey Bill, what OT would be best if I wanted to go with your Octal socket conversion kit for 6v6′s mod and your aux jack to run a 16 ohm cabinet?
The 8 ohm-16 ohm mismatch isn’t too bad, so either OT would work. If you want maximum efficiency, maybe you can rewire your cab for 4 ohms and use the 4 ohm lead on the TO22.
Thanks a lot for the education on how to make this amp sound great. I Just installed the TO20 & basic mod & twin stack after switching to JJ output tubes, Electro Harmonix preamp tubes, and a Texas Heat speaker. Wow. This is NOW an awesome amp.
Each of these was one step closer, but combining them all was the real key. I appreciate your specific directions and resourceful web site, they made doing it myself seem easy.
Bill – Have You done any experimenting with the speaker cable? I see these Monster combo amp speaker cables that claim to “deliver tight, punchy bass and incredible dynamics”. Just wondering what you thought of those/ if you’ve tried them? if it would make any difference at all?
Thanks, Scott.
For a 15 watt amplifier, 18 gauge wire is fine. It’s rated for 1200 watts in hair dryers and such. If you want to go larger, fine, but all that stuff about oxygen-free wire and the super-thick cables is completely unnecessary.
Bill,
I’ve been playing (and building) tele’s for a long while and I enjoy solid clean to country-blues SRV tones. I would like to build an amp like the BJ and I’m interested in building one with many of the modifications that are shown on your site But I’m not starting with and amp, just schematics you find in service manuals etc. Some questions I have are what transformer would be recommended with 5881 tubes? and what power transformer would you recommend? Between the schematics, could you direct me with what design “mods” I should build into the amp. I would incorporate ‘real’ pots in the construction and whatever good sense things that should go into an amp, like the on-standby- progressive switch. And the presense control.
Thanks!
Glenn
I wouldn’t try to build a Blues Junior from scratch. For what you’re describing, an Allen Amps Sweet Spot would be an excellent choice–and you’ll have a real boutique amp when you’re done. If you want to go lower-rent, a Weber Princeton kit would be good, too.
Developing a layout from scratch is a lot of work. Sourcing all the components is also time-consuming and expensive. A kit will save you money and probably give you a better end result.
Bill, I am building a Blackface Princeton Reverb from scratch, but am having trouble choosing the OT, TO20 or TO22? I play surf music, and favor Jaguar and Jazzmaster guitars – thanks
Either will work fine. The TO20 is smaller; the TO22 has 4/8 ohm switching. They sound pretty much identical.
Hi Bill,
I just sold my 100 watt Marshall and started gigging using a BJ with pedals. I love that I can crank on this thing and get a nice tone and reletively low volumes. I replaced the speaker in one with a Celestion Greenback and in the other with a Vintage 30. (I bought two BJ’s cause I love them so much!) I wanna run an extension cab. The speakers in the amps are 8 Ohm. The cab can be switched to either 4 or 16 ohm. I’ve been running it in series, 8ohm amp speaker with 16 ohm cab, giving me about 24 ohm load I’d guess. I was thinking maybe this transformer upgrade would allow me to run series with an 8 ohm amp speaker 4 ohm cab giving me about 6 ohm. Would a tranformer upgrade allow me to safely run down to 4 ohms? What would you do? How touchy are the Juniors once you start moving away from 8 ohm operation?
Thanks
I prefer speakers in parallel. 24 ohms is too high, and can cause damage. You should try running the 16 and 8 in parallel, although the 8 ohm may hog some of the output. Tube amps generally prefer lower impedance, not higher. So the 16 and 8 in parallel would give you 6 ohms. With that, you could run either the 4 or 8 ohm tap on the TO22.
Thanks for the quick reply. I’ll need to order a new T022 next week then. Do you mind me asking we do you prefer speakers in parallel? Also, what is being damaged by running at 24 ohms? It’s my understanding that its ok to go higher than recommended just not lower, or is that only with solid state amps?
Speakers in series interact more with one another, usually not in a good way. It’s worse on low notes and especially bad for bass. Also, if one speaker fails, you have an open circuit, which is very damaging to the output transformer. It causes flyback voltages and arcing inside the transformer or output tubes. The BJr has suppressor diodes to absorb flyback voltages, but it’s best not to have them at all. High impedance has the same effect as an open circuit. The amp tries to push current into the speaker and fails. Magnetic fields build up in the output transformer, and when they collapse, they cause high flyback voltages.
Solid-state and tube amps are opposites. SS can have an open circuit or really high impedance and not care. Low impedance or a shorted output can melt the output transistors. Tube amps need a low impedance and can run into a shorted output for a while without damage. That’s why tube amps have a shorting switch on the speaker jack and SS amps don’t.
Hi-
I have a Pro Junior. Your TO20 sounds very intriguing. I understand that the basic mods as you describe would provide the best results. Do you have a kit for the Pro Junior? Can I use the same kit as the Blues Junior?
Thanks
If you let me know it’s for a Pro Junior, I’ll prep the leads to the right length and install the right connectors. I don’t have a basic mods kit for the PJ, but the amp does respond well to power supply stiffening — doubling the 47uF filter cap. I also have instructions for installing adjustable bias.
A friend of mine and I are in the process of ‘modding’ my cream board blues jr. The instructions for the TO20 transformer says to solder blue capacitor across R30. This, according to what my common sense tells means, remove and replace R30? Not put it on the back side. Thanks, sorry if its a dumb question. I’m excited to hear the transformation when we’re through.
Peace
Leave R30 in place. Connect one leg of the blue cap to one leg of R30. Connect the other to the opposite leg. See here:
http://billmaudio.com/wp/?page_id=115
Last picture on the page (the cap is not blue in the pic).
BillM…..my Jr. died….just stopped working? Fortunately I have another. I already replaced the fuse with no luck. What’s next, transformer????
Unlikely that it’s the transformer. Is the pilot light on? Do the filaments light? Do you have a filament fuse as well as a main fuse in yours? Is there hum?
Thanks for the reply. No pilot light….no hum….tubes do not glow….it is just like it is turned off….nothing. I’m not aware of a filament fuse…its a stock unit, but I did put a properly rated Celestion 8ohm GreenBack in it and it worked great for a few months. I’ll go back and recheck the connections, but it was working fine! I turned my head to look at something on the screen and when I turned back it was dead. No snap, crackle or pop, no nothing cooked on the mother board, very strange. We were having summer storms that day, but nothing else re-booted, lights did not dim. I have a spare and I guess I could start swapping parts, but I’d rather just replace the defective part. Any guidance you can provide would be apprecieated.
Jerry
If the fuse is intact (check it with an ohmmeter) and it still doesn’t work, check the pairs coming off the power transformer for voltage. If nothing’s coming out, you probably need a new PT. Make sure first that AC is actually getting to the PT. If you can see AC on both sides of the fuse, if it goes on and off with the power switch, you’ve pretty much narrowed it down to the PT.
Hey Bill,
I have an unmodded UK 240v blues junior. I have just moved to Brazil where they run 110v. Can I drop in one of your 110v upgraded transformers straight into the amp and run it at 110v in Brazil, or would any other changes need to be made to a factory 240v amp?
Thanks
You just need the 120V power transformer. Everything else is the same. I don’t sell power transformers, but you can get it from Mojo Musical Supply. Their overseas shipping is expensive, so you may be able to get it less expensively from a Fender dealer or repair shop in Brazil.
Hi Bill:
Great site, best info source for Blues Jr and tube amps in general found anywhere.
My question, if I wanted to put a T020 and 6V6′s into a Pro jr, I would not be able to do the cathode follower mod because both preamp tubes are fully utilized. Would doing these mods without the CF mod be OK?
Thanks in advance
Yes, you could do the 6V6 conversion without the cathode follower mod and it would work just fine. 6V6s need more bias voltage than EL84s, however. With a 50K pot in there, you would probably have enough range, but I haven’t tried it or tested it. You might have to rework some other values in the bias supply.
Hi again Bill
One more question. Could the 5881 be run in the pro Jr, with the mods mentioned above. (T020 OT, octal sockets, bias rework)
The 5881 requires even more bias voltage than a 6V6 and the heater draws more current. At full power, the power transformer will probably not have enough total volt-amps to supply full heater voltage and high voltage. Proceed at your own risk.
Bill
I have a Blues Jr that I would like to mod but I am not wanting to spend a hundred bucks or more for a temp controlled weller in addition to the mod costs. I have a new 25 watt weller in hand. Will that not do the trick? I am thinking basic mods and output transformer to start. Also I put a 8 ohm cannabis rex in and have a extension cab with a 16 ohm v30. It sounds like its ok to run both together in parallel with the stock OT and your upgrade OT’s?
Thanks
A temperature-controlled iron makes the job easier, but if you have good soldering skills and work quickly and cleanly, you can use anything short of a blowtorch.
Yes, you can run the 16 ohm extension speaker in parallel. The combined 6 ohm load won’t cause any problems. The 8 ohm speaker will hog more of the signal because of the lower impedcance, however.
Hi Bill:
How do you feel about tube versus solid state rectifiers in amps in general and in the blues jr? Is it worth investing in if you are trying to get that clean vintage sound from a B Jr? If so what tube do you recommend?
Thanks again
The Blues Junior is what it is. I would not recommend trying to install a tube rectifier. The BJr has plenty of breakup and touch-sensitivity, especially in modded form.