Let's build a blues junior

[hesamadman]

Hey guys. Corey from RDK here. Been a while since I've been on. The last builds were a success. I've spoke with a lot of you guys personally about mods on it and I STILL have yet to do them. Ha ha (Silvergun. One of these days. I have a couple ideas I'll talk more about those later)

My beautiful lady and I are expecting our first little one so shop work has gone down a ton and field work (since I'm an electrician full time and that's where I make my money) has taken an increase.

Anyway. How about it? Anyone build a blues junior? Thinking about it since it's such a great little amp. What are your thoughts?

[HotBluePlates]

A quick internet search turned up an "In-Store Used" Blues Junior for $350. Ebay completed listings show them selling at that price or well below.

You might have a hard time building that for the same price you can buy it.

I'd look for a used one, and tweak it if necessary. I did exactly that with an Epiphone Valve Junior combo ($70 like new at my local pawn shop).

[hesamadman]

A quick internet search turned up an "In-Store Used" Blues Junior for $350. Ebay completed listings show them selling at that price or well below.

You might have a hard time building that for the same price you can buy it.

I'd look for a used one, and tweak it if necessary. I did exactly that with an Epiphone Valve Junior combo ($70 like new at my local pawn shop).

Thanks for the input man. It's not so much about owning one as it is hanging out in my shop and building it and watching the Billy Jack movies :)

[Willabe]

My beautiful lady and I are expecting our first little one.

What are your thoughts?

(Yes I chopped it.)

Here's my thought's!

Dad, amps and guitars come and go, but a wife and kids?

HEY, HEY, HEY!       A NEW BABY given to you and your wife!!!!!!       
   

         Prayin for you and yours to be,    Brad   

   

[tubenit]

Anyone build a blues junior? Thinking about it since it's such a great little amp

I might consider buying one if the price was low enough, but I personally would never build one. I don't think they sound that great.

IF you are wanting an 18w type amp with reverb, I think there are many better choices available.  Geezer's HoSo56 would probably be my first choice.  IF you are interested in that, I will draw up a layout board design for you. 

I'd rather build an incredibly great sounding amp than a just "OK" amp that I could go buy. Having said that,  IF you truly prefer the Blues Jr. tone, I think you should build that.

With respect, Tubenit

EDIT   2-1-2019     I've revised the ExpressSCH schematic with minor changes and added a matching layout.  CHECK for ERRORS!

[jjasilli]

I say go for it.  IMHO the Blues Jr. sounds great stock; better with some tweaks (see the Bill Machrone web page).  But Fender's build quality is poor.  The amp doesn't stand up to use.  The same circuit on eyelets or turrets, with chassis mounted tubes and pots is a fine plan.

Alternatives:  buy a used or broken one, or even a new one cheap enough.  Use it until it inevitably breaks; then gut it and re-build. 

[SILVERGUN]

Hey Corey, welcome back and CONGRATULATIONS!
Most of what I've seen and heard about the Blues Jr. have been tweaks and mods, and like jj said,,,check Bill M's site
And then try to incorporate these mods into your initial build,,,,,so you wont have to work backwards
My friend brought me one of these and I did the "tone stack mod" and it was an improvement over stock

One of the biggest articles over @Bill M is where he builds a "special" blues junior, and converts to 5881 output tubes (which, in my mind, means it's not really a Blues Junior anymore  )
And that's probably what I would do too.....except then you need all new iron, etc., etc....
I personally am not a big fan of the EL84 output tube tone, and I wouldn't start a new amp build with that plan....this guy went to a lot of trouble to take a stock amp, and then change everything about it 

So I thinks it's a good idea to start fresh...
Just my 2 cents......and it might serve you well to let us know what you want to accomplish with this amp...tubenit has built and designed many great amps.....his advice is invaluable,,,,as well as all of the other opinions you'll get here....nothing beats experience

I wouldn't want to talk you out of what you want to do, but I would like you to be as informed as possible to make sure you build something that you will LOVE......many guys have built many amps only to find out that they weren't exactly what they wanted them to be.....so sad

[phsyconoodler]

Ok. I had a fried Blue Jr come across my bench a few years back.What to do,what to do.
  I looked at the charred board and proceeded to gut it and built a Princeton Reverb into the chassis.I used all the same control descriptions on the panel but it was 100% Princeton Reverb inside.I used the transformers from the blue jr as well.
  The result? A killer sounding,low voltage Princeton Reverb with a master volume,treble mid bass controls.
It is still in regular service and sounds amazingly good.I simply bolted on Belton tube sockets into the existing holes in the chassis,added one extra preamp tube hole(easy) and Voila!
  Install great sounding amp where a mediocre Blues Jr was before.The stock transformers actually worked great too!It is fixed bias with basically the same bias supply as a Princeton Reverb taken off one leg of the Primary PT winding.

[tubenit]

I looked at the charred board and proceeded to gut it and built a Princeton Reverb into the chassis.I used all the same control descriptions on the panel but it was 100% Princeton Reverb inside.I used the transformers from the blue jr as well.
  The result? A killer sounding,low voltage Princeton Reverb with a master volume,treble mid bass controls.
It is still in regular service and sounds amazingly good.I simply bolted on Belton tube sockets into the existing holes in the chassis,added one extra preamp tube hole(easy) and Voila!
  Install great sounding amp where a mediocre Blues Jr was before.The stock transformers actually worked great too!It is fixed bias with basically the same bias supply as a Princeton Reverb taken off one leg of the Primary PT winding.

I think that is an excellent idea!  I like it.

with respect, Tubenit

[Parkside]

Hi There

I was going to start a post on this topic, but I did a search and PsychoNoodler has done exactly what I want to do.  (though this thread is old this seemed like the best place to start)

I want to gut a cream board Blues Junior that I own, and install a hand wired Princeton Reverb circuit. 

Looking through the Hoffman page Im not sure what parts I'll need to order, so I wondered if anyone here could shed some light on the subject. 

From the BJ, I have the Cabinet, Chassis, Reverb Tank, Speaker (a 12" which I may change for a 10" with corresponding baffle board), and all the other bulky heavy-cost-to-ship items. 

I need to buy a turret board (Im assuming I'll buy the Blues Junior board and wire the princeton schematic..?) and I Guess a handful of resistors, caps etc. 

Just wondering if anyone could offer a bit of guidance on this.  I have modded amps before, repaired a few things, but this would be my first build. 

Thanks everyone
Dave

[hesamadman]

Size wise, the correct Hoffman Princeton board should be fine but measure to be sure. Reverb tank is an 800ohm in and like either a 1200 or 2200 out. I'm thinking that probably won't work like it should with Princeton tube reverb. BJ reverb is solid state. I also don't think you will like the results of the OT of the BJ with the 6v6 of the Princeton. But then again you may like it.

[sluckey]

The BJ PT is wrong for the PR circuit. It doesn't produce enough B+ or bias voltage.

[Parkside]

Hmm.  Thanks guys

Ok, full disclosure.  The BJ I'm trying to mod has already been modded.  I put in the BillM Octal conversion kit 6v6 instead of el34's and upgraded Transformer.  Made it 40 watts...but I don't like it (did this maybe 2 years back)

I like the princetons Reverb 15w sound with the 6v6.  Essentially I want to turn the amp up to 9 and not have the band throw things at me for it being obnoxiously loud.  I tried a PRRI at the shop yesterday and it seemed right on the money.  turned in up to 9, a few ppl looked over annoyed, but the whole store wasn't running over to strangle me. 

I own:  A 67' BF super reverb, way too loud past 2 (no break up), A 71' Vibrolux, way too loud past 2 (no break up), a 67 BF Deluxe Reverb (way too loud past 3, bassy, no break up), and 2 BJ's; a slightly tweaked el34 original, and the Octal converted one we're talking about.  The el34 one is ok...but, not great, and I don't like the Octal as is at all. Just flat and lifeless (lots of tubes/speakers have been tried)

So Basically Im thinking Hoffman PR kit, in a BJ box

[Willabe]

I put in the BillM Octal conversion kit 6v6 instead of el34's and upgraded Transformer.  Made it 40 watts...

The blues Jr. has EL84's not EL34's. And your 2x6V6's is maybe ~20w not 40w.

Unless you meant 6L6's? But the new PT must have enough B+dcv and B+ current to get ~40w output.

I like the princetons Reverb 15w sound with the 6v6. ..........

......... a 67 BF Deluxe Reverb (way too loud past 3, bassy, no break up), .......

There's not much volume difference at all between a PR (~15w) and DR (~20W). Yes the PR has a 10" speaker and the DR has a 12" speaker but if you put the 2 side by side and A/B them with the same guitar/same settings not much difference.   

[labb]

Does anyone build the Marshall 18 watt any more? Use to be pretty popular.

[Parkside]

Yes right, I did mean 6l6's

Here's the link: http://billmaudio.com/wp/?page_id=1098  and its 30 Watts not 40.

There's not much volume difference at all between a PR (~15w) and DR (~20W). Yes the PR has a 10" speaker and the DR has a 12" speaker but if you put the 2 side by side and A/B them with the same guitar/same settings not much difference.   

I can only comment on my experience.  Anything past 3 on the BFDR and I'm the loudest thing on stage by a fair margin.  Not sure why, its just loud, breaks up around 5 or 6 with the bias run a bit on the hot side.  The princeton was loud'ish' at 9, but loud like "this is a normal volume to play at with a drummer, a little aggressive for a music store"   The DR at 9 they would have flipped out. 

Maybe i'll rent one and see, but I think its what I'm going for.  I want the amp to do 90% of the heavy lifting overdrive wise and pedals to just take it that last bit over the top.  Currently all my amps get to about 2-3 and are clean and then the pedals create all the grit. 

[eleventeen]

I am surprised at your BFDR commentary. But maybe you could "tame" it by substituting lower-gain tube(s) most especially for V1. The "grail" tube for this type of thing is a 5751 or a 12AY7. When we say "V1" we generically mean the first tube your guitar signal sees inside the amp. The "V1" of the REVERB channel in a 2-channel BF or SF Fender amp is going to be the SECOND small tube.


But you can try this for free, very easily, by swapping the 12AT7 phase inverter tube which is the small tube closest to the power tubes, with what we now know is V2 in your BFDR. Or if you happen to have a spare lower-than-12AX7 gain tube in this family. I'd certainly try it.


Gain factors:
12AX7= 100
5751  = 70
12AT7= 60
12AY7= 45
12AV7= 41
12AU7= 19




A 12AT7 is the normal reverb driver tube (the third small tube) and many folks find themselves with too much reverb in a Fender. I myself never turn the reverb up over "4" and it's on the hairy edge of "too much" up there. Solution? Many folks replace the 12AT7 with a 12AU7, the lowest gain member of the family.


But with very little effort, you can at least try out a 12AT7 for your first preamp by making the swap reco'ed above.

[sluckey]

With that PT you should be able to build a PR (or DR) in your BJ cab. You will need a 4AB3C1B reverb tank. It's 16.75" long. Hopefully the BJ cab is wide enough.

[Parkside]

Thanks guys

Ive messed around with the tube stuff, know my Plates from my Cathodes, My Phase inverter from my rectifier, etc. 

The minimal experimentation I've done with the topology of the the DR, pulled V1 for faster break up in 2nd channel (I only use the 2nd channel), and I tried putting the 12AT7 in V2.  I just...didnt like it as much, it was slightly quieter, but a lot of the gain left with the volume.

I think theres a reason that the Deluxe and Princeton exist, too.  I don't know if I just have a loud Deluxe, but like I said, its pretty ripping (messed with different speakers too, I own and use an attenuator sometimes, though I feel it does colour the tone somewhat)

The other thing that I think bares mentioning (which is often not discussed in amp tones forums) are the guitars used.  When certain guys say, "my Dr isn't that loud" it makes sense, especially when it turns out the poster is using a Strat or a Tele, with single coil pickups.  I play a Gibson SG (Derek Trucks signature) so, these are the results I'm getting, in relation to that guitar. 

Thanks for all the advice, I definitely consider it all helpful.

Dave

 

[Ritchie200]

Hey Corey welcome back!  SO, the big sparky has a little spark on the way?  Oh how your life will change - for the better!  Are you sure you shouldn't be concentrating on a headphone amp?

Jim

[Willabe]

Anything past 3 on the BFDR and I'm the loudest thing on stage by a fair margin.

I am surprised at your BFDR commentary.

Me too.

You must be playing with a very experienced drummer with great stick handling control if your DR on 3 is louder than the drummer.

I don't know if I just have a loud Deluxe.....

There are other possibilities if there's that much difference between your PR and DR, there's something wrong with the PR (bad/worn/weak/tubes, failing/dying filter caps, weak/dying cathode bypass caps, drifted resistors.....) and/or the speakers in 1 or both amps are causing it.

There's more than just a speakers size and wattage ratting, there's also a db sensitivity/efficiency rating. Some speakers are more efficient and are surprisingly louder with the same amp than less efficient speakers of the same size and wattage.   

I think there's a reason that the Deluxe and Princeton exist, too.

Sure, price point for sales/market. It wasn't about a big jump in volume. Fender just squeezed out the last few watts available from a pair of 6V6's in PP, class AB, grid bias.

The PR was a single channel amp, DR was a 2 channel, so you could plug a 2nd instrument or a mic it too. PR was more of a student model albeit with reverb and tremolo (Fenders top of the student line model?) and the DR was a bit more because now your buddy/band mate could plug in too or you could plug that mic in and sing along with your guitar playing in your 1st garage/basement band.     

The other thing that I think bares mentioning (which is often not discussed in amp tones forums) are the guitars used.  When certain guys say, "my Dr isn't that loud" it makes sense, especially when it turns out the poster is using a Strat or a Tele, with single coil pickups.  I play a Gibson SG (Derek Trucks signature) so, these are the results I'm getting, in relation to that guitar.

If you are comparing the 2 amps in an A/B test with your (same) SG then it shouldn't matter if their bucks in it or single coil PUP's. Now if you were running the SG through the DR and a Strat through the PR with both amps volume and tone controls set the same then there there will be some/more difference in output volume. But there still shouldn't as much difference in output volume as you describe it.     

Going from Strat single coil PUP's to a Gibby with bucks for the most part only causes amps to break up sooner on the amps volume setting. (I have played both types for 30+ years.) Once you get to a certain point on the amps volume control the amp doesn't really get any louder, it just breaks up more.

Any amp can only put out so much power/db's because it's being governed/limited by the amps power supply, it's preamp/PI, the power tubes and the speaker(s). 

[Parkside]

sooooooo....

....Anyone know how to build a PR into a Blues Junior?   

[sluckey]

You strip out everything you don't need then start putting PR stuff in.

It would help to see some pics of the outside and inside of the chassis to see what you're up against.

EDIT... I just looked at the pics of Hoffman's BJ conversion. You're gonna have to plan this carefully. The PR needs 7 tubes so you will be adding two. Check the measurements of Hoffman's PR board to see how it will fit your chassis.

I suggest you start a new thread on this project.

[hesamadman]

sooooooo....

....Anyone know how to build a PR into a Blues Junior?   

Lets just start from the beginning. You will get any help you need here I promise. Gut the amp. Are the sockets onboard? If so you wont be needing those. Are they chassis mount? If so, re-use them. Leave transformers intact (for now). Post some photos. We can go from there. 

[hesamadman]

Hey Corey welcome back!  SO, the big sparky has a little spark on the way?  Oh how your life will change - for the better!  Are you sure you shouldn't be concentrating on a headphone amp?

Jim

Hey Jim,


I posted this thread in 2013. Parkside saw the post and found interest since he is building a BJ into a PR. I however did not build the BJ. Instead I focused on a 30 watt el84 amp at the time. I have built myself 3 variations so far. My little girl is now 2 years old  . Believe it or not I don't have a single amp at home. Just my acoustic. But youre right about the headphone amp. I actually moved my shop before my daughter was born as I knew I would never get any work done with all the naps. 


Since shes 2 now I think I'll bring myself an amp home.

[Parkside]

Ah, thats a good start, i didn't see the BJ conversion photos before. 

Looks like reverb needed to be scrapped entirely (neither solid state or tube driven, from what I can see...just no reverb.)

Ill post some photos asap. The original BJ Tube sockets were mounted on a separate circuit board.  As shown in photo 1:  http://el34world.com/Hoffman/Blues_Junior_Build.htm

After the Octal conversion I did, the 2 6L6 sockets are mounted to the Chassis, and the PCB they used to be mounted to, was cut in half, like this: 

http://www.duhvoodooman.com/miscimages/musical/BJr/BJr_mods_rear-down.jpg

So, the initial big picture problems are going to be: 

Im going to need to add another preamp tube, as BJ's only have 3 12ax7's
Im going to need to add a Rectifier tube.  I think I have the physical real estate, but haven't measured. 
And I may need to abandon reverb (which may be a deal breaker, the compromise makes it less interesting to me)

Either way I'll post photos and more info as I go.
Thanks guys

Dave

[Ritchie200]

I actually moved my shop before my daughter was born as I knew I would never get any work done with all the naps. 

[/quote]

Her naps or yours!

Wow, I didn't even look at the date on this....  Old age.  I got to thinking that I've seen you post recently, but again.... Old age.

Jim