1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

Pro Jr. based on a previous amp design?

Discussion in 'Amp Central Station' started by klasher, Aug 18, 2019.

  1. jsnwhite619

    jsnwhite619 Friend of Leo's

    Age:
    36
    Posts:
    3,237
    Joined:
    Sep 10, 2013
    Location:
    Georgia
    One thing I've noticed while comparing Pro Jr schematic to other amps is that it seems like the Pro Jr has way more components than I would expect for a "simple little amp". Glancing back just now, I see up to R33 and C21 on there - I may have missed something. That's 54 resistors & capacitors plus everything else to make it work, all for a single input, two knob amp. That being said, I really have loved mine though it's in a pine cab with a Ragin Cajun now. And I have been reviewing PJ stuff the past couple days because I think I'm ready to recap it and maybe mod try a few common mods to it.

    But, there just seems to be a whole lot in there for such a "simple" amp.
     
  2. fasteddie42

    fasteddie42 Tele-Afflicted

    Age:
    31
    Posts:
    1,224
    Joined:
    Dec 10, 2016
    Location:
    Tip of the Mitt
    uh...

    pro juniors deftly cop a "fender tone"
     
    stefanhotrod and tery like this.
  3. E5RSY

    E5RSY Doctor of Teleocity

    Posts:
    10,949
    Joined:
    Mar 5, 2009
    Location:
    Georgetown, TX
    Be interested to know what you end up doing relative to any mods and the results.

    The only thing I've been tempted to do is to cool off the bias a little by changing the appropriate resistor (R25, I think???).
     
    Last edited: Aug 19, 2019
  4. jsnwhite619

    jsnwhite619 Friend of Leo's

    Age:
    36
    Posts:
    3,237
    Joined:
    Sep 10, 2013
    Location:
    Georgia
    The bias is definitely high on the list. Probably increase the filter cap values. After realizing it doesn't have any bypass caps on either preamp tube, I'm curious how that would sound. Maybe cooling off the bias to a comfortable level and a bypass cap on V1 would balance each other out -- boost the preamp gain but clean up the power tubes? I never run it maxed out like a lot of people seem to do, so earlier overdrive would suit me ok I think on the preamp.

    Probably try to find something to cut some brightness. It's way too bright after 4 or so on the tone and always has been. Unlike my tweed style amps that just increases crunch with the tone knob cranked, my Pro Jr seems to just increase the high end bandwidth to painful levels as you crank it.

    I'm not in the mindset of completely transforming it, I like it well enough. But, a little more bass and smoother top end would probably make me fall in love with it again.
     
  5. zombiwoof

    zombiwoof Tele-Afflicted

    Posts:
    1,235
    Joined:
    Oct 17, 2008
    Location:
    Tujunga California
    There is a good reason why Fender and other amp makers suddenly came out with EL84 amps. Some years ago there was a period when NO 6V6's were being made. In order to still put out lower wattage amps, they all adopted the EL84 tube, which had only been used sporadically in the past. That is the reason, no 6V6's being made at all. Within a few years modern tube factories started making 6V6's again, and the 6V6 amps started returning. We went through the same thing with EL34 tubes when the last factory (Tesla) making them shut down. Even Marshall had to change to Sovtek 5881's for a while, which they would never had done if there were modern EL34's being made. As soon as more EL34's came out on the market, Marshall reverted to them.
    Many players don't remember or weren't around when the last great US and Euro tube factories went under, there was a period of time when we didn't know if we were ever going to get new tubes made again in the popular types. It was a weird time, but the Russian and Chinese factories got it back on track.
    Al
     
  6. jrblue

    jrblue Friend of Leo's

    Posts:
    2,280
    Joined:
    Nov 14, 2010
    Location:
    Santa Barbara
    My first-issue, USA-made Pro Junior is a phenomenal amp, not because it is an old Fender retread, but because it isn't. Given the tube complement, it's going to be its own thing, and if you're looking for a cheap recreation of some particular vintage Fender, what the heck are you doing with an EL84 based amplifier? There are some crappy components in a PJ and some cheap build methods used, and if you change out that crap (as I did) it becomes a much better, reliable amp. Jeff Beck has toured with the PJ, so those who claim it to be a lousy amp because it doesn't emulate old Fenders can keep that hangup to themselves. I did a bunch of mods to mine, and some tube swaps, too, and the end result is loved by all who hear it or play through it. A bigger OT, a choke, removing a treble bleed cap, and beefing up the filter caps made mine a tone monster. My more $$$ amps are largely silent because the PJ gets the use.
     
  7. Dacious

    Dacious Poster Extraordinaire

    Posts:
    8,863
    Joined:
    Mar 16, 2003
    Location:
    Godzone
    Marshall didn't deviate from EL34 tubes except in limited models like the budget JTM30. They even went 6V6 in the Studio 15.

    I don't think a lack of manufacture was the reason Fender went EL84. Price and marketing were more likely the cause.


    There's always been 6V6 and EL34 tubes available from one vendor or another. The Deluxe Reverb Reissue has been in continuous production since 93 - the same year the Pro Jnr was released. Sovtek and Chinese tubes were available.

    Fender and others probably went EL84 because the buyers were in a PR-driven thrall to Voxoid amps (this was also when Matchless, Trainwreck, Bogner and other boutique makers plus Mesa EL84s amps like Studios and Callibers were headline news) - and the tubes were a fair bit cheaper to use taking into account the smaller transformers/real estate needed. PV got into Classics around then plus Vox made a big resurgence with the Brit AC 15, 30.

    Fender's tube amp offerings were dying in the market in the early PCB red-knob/black knob era. Trying EL84s has arguably brought them back via the bloodbath entry amp market - but all their pro-grade and Custom Shop amps certainly don't use them.
     
    King Fan and peteb like this.
  8. jsnwhite619

    jsnwhite619 Friend of Leo's

    Age:
    36
    Posts:
    3,237
    Joined:
    Sep 10, 2013
    Location:
    Georgia
    Sounds about right to me.

    From a Dave Hunter article in Premiere Guitar:
    From the late eighties to late nineties no reliable current-manufacture 6V6s were available, so few manufactures designed new amps around this tube. This is the course of events that led to the virtually unthinkable release of smaller Fender amps that used EL84s, such as the Blues Junior (the early-sixties Tremolux, which briefly carried EL84s, being something of an anomaly). The release of a rugged and reliable 6V6 first from Electro-Harmonix, then from other contemporary makers, has led to a renewed popularity for this tube, and it proliferates again in the twenty-watt-and-under range.

    https://www.premierguitar.com/articles/Everything_You_Ever_Wanted_to_Know_About_Output_Tubes?page=1
     
    redchapterjubilee, King Fan and peteb like this.
  9. peteb

    peteb Friend of Leo's

    Posts:
    4,208
    Joined:
    Apr 25, 2003
    Location:
    Cascadia
    Pro junior date of first production 1993

    DRRI date of first production 1993

    Blues Jr. date of first production 1990



    EDIT: source is Wikipedia.
     
    Last edited: Aug 20, 2019
  10. E5RSY

    E5RSY Doctor of Teleocity

    Posts:
    10,949
    Joined:
    Mar 5, 2009
    Location:
    Georgetown, TX
    The Blues Junior was actually the last to join the series, originally called "the Tweed Series" (Blues Deluxe, Blues Deville, Pro Junior, Blues Junior. Fender also included the solid state Bronco in the series, too.).

    I know Wikipedia says 1990, but the Teagle & Sprung book says the Blues Junior came later, in 1995, whereas all the others were 1993.

    I trust the book.
     
    peteb likes this.
  11. El Tele Lobo

    El Tele Lobo Poster Extraordinaire Silver Supporter

    Posts:
    5,639
    Joined:
    Oct 21, 2014
    Location:
    Florida
    I would just save up for a tweed champ clone...but, in a pinch, the Pro Jr. is not bad. I liked the Blues Jr better originally, but only later learned to truly appreciate the Pro Jr.. Now, I'd rather have the Pro Jr. than the Blues Jr., if I had to choose between the two.
     
  12. jsnwhite619

    jsnwhite619 Friend of Leo's

    Age:
    36
    Posts:
    3,237
    Joined:
    Sep 10, 2013
    Location:
    Georgia
    Here's two Pro Jr sound clips I've done in the past. Both in 16x20x10 pine cabinets with birch baffles, one with a 12ax7 in V1 and an Alessandro 12" speaker. The next was with a 12ay7 in V1 and a Cannabis Rex 12" - actually, the cabinet in my avatar. Both sound like Fender amps to me. The 12ay7 clip has great Fender clean tone.

    So, as far as design inspiration, I don't know how much lineage it has to the old classics, but it still is a Fender to my ears.

    Dirty tone with Alessandro.


    Clean with C Rex
     
    Daytona.57 and peteb like this.
  13. maxvintage

    maxvintage Friend of Leo's

    Age:
    61
    Posts:
    4,971
    Joined:
    Mar 16, 2003
    Location:
    Arlington, VA
    IMHO the Pro Junior is a great amp

    I'm a jazzbo and usually play on the neck pickup. I'm looking for kind of a kenny Burrell sound. The pro junior is great for that out of the box. I made a 12 inch pine cab for mine and put a weber alnico in it. I put a 12at7 in V1. Gets a really fantastic tone, ot of clean headroom, really nice mild breakup, not too edgy but lots of clarity.
     
    Daytona.57 likes this.
  14. Commodore 64

    Commodore 64 Friend of Leo's

    Age:
    45
    Posts:
    4,180
    Joined:
    Mar 1, 2010
    Location:
    Kent, OH
    Same here, though I didn't bother with the choke.

    Also, to OP. Depending on when your PJ is made, it may have a bypass cap on V1 cathode. They stuck em on there after 1998. I like it better without, more than enough gain in that circuit to drive an EL84.
     
  15. peteb

    peteb Friend of Leo's

    Posts:
    4,208
    Joined:
    Apr 25, 2003
    Location:
    Cascadia

    Thanks. I also find T&S to be a very reliable source.





    It’s like the eternal question.




    Which came first, the pro jr or the blues jr? I could see it going either way.





    If the DRRI and the pro jr both came on line in 93 could it be that there were 6V6 tubes available but not enough to go around? Not enough for the tweed series, which they predicted would be a huge seller.
     
    E5RSY likes this.
  16. scelestus

    scelestus Tele-Holic

    Posts:
    534
    Joined:
    Jun 24, 2018
    Location:
    Michigan
    I certainly won't disagree about Fender's move to EL84, but Marshall definitely produced flagship amps with 5881 output tubes. The JCM900 4100s were produced with 5881s for several years - there are loads of forum posts online where people debate about them and discuss converting to EL34 bias specs.
     
    SixgunElectric likes this.
  17. Little Ricky

    Little Ricky Tele-Holic Silver Supporter

    Posts:
    917
    Joined:
    May 11, 2008
    Location:
    Mid-Atlantic
    The easiest change is the swap the 12AX7 in V1 for a 12AY7, or even lower gain 12AU7. This makes the off/on volume change at 2-3 on the Volume knob less dramatic. After this change I keep the volume around 8. It gets loud around 5, around 6 more bass comes in, and it’s perfect for me at 7-8.
    I also put a 12AT7 in V2. I think this tube is higher current and this is beneficial for the phase inverter (not sure if I’m right about that).

    Since I was already opening the amp to change the filter caps,

    I lowered the bias a little by switching one resistor.
    I added 25uF bypass caps to V1 and V2. This adds just a bit of bass and clarity to the sound.

    I have an older one with blue alnico speaker.
    I totally recommend changing V1 to 12AY7, very cheap and easy.
     
    Last edited: Aug 20, 2019
    Daytona.57 and jsnwhite619 like this.
  18. Dacious

    Dacious Poster Extraordinaire

    Posts:
    8,863
    Joined:
    Mar 16, 2003
    Location:
    Godzone
    You're right - the early 4100s did come with them. But that didn't last long. One of the retailer's here noted one shipment only.

    Given the 900 was Marshalls 'CBS era' cost would probably be a big factor.
     
    scelestus likes this.
  19. scelestus

    scelestus Tele-Holic

    Posts:
    534
    Joined:
    Jun 24, 2018
    Location:
    Michigan
    I think the 6100s came with them too, but they were indeed quickly replaced.
     
  20. jsnwhite619

    jsnwhite619 Friend of Leo's

    Age:
    36
    Posts:
    3,237
    Joined:
    Sep 10, 2013
    Location:
    Georgia
    Yeah, I built a 16x18 pine cab for it a few years back. Ragin Cajun. A 12ay7, a Blues Driver, and my Les Paul can get some heavenly rock tones. But, who says you can't make it even better?!

    Really, the ice pick treble is my only complaint. And I have some F&T caps on hand that ought to do a little better than what's in there at this point.

    Sent from my XT1585 using Tapatalk
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.