Pro Jr. based on a previous amp design?

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

  1. klasher

    klasher Tele-Holic

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    Any idea what previous amp Fender based the Pro Jr. on? Or is it a unique design?
     
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  2. maxvintage

    maxvintage Friend of Leo's

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    It was designed, according to the internet, by Bruce Zinky. The internet claims it’s similar to a tweed tremolux. I don’t know enough to understand if this is true
     
  3. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    EVERY amp is based on a previous design. There are only so many ways you can hook up a 12ax7 and make it amplify. Fender pulled their stuff back in the 40s straight out of the RCA tube manual, which is why the older tweed amps have the "circuits borrowed from" sticker next to the tube chart.
     
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  4. peteb

    peteb Friend of Leo's

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    The most vintage feature of the pro jr is the tone control.

    Tone controls were used on many older circuits, big amps up to about 55 and the small amps kept the tone control thru the brown face amps.


    The pro jr has a push pull power section, a long tail phase inverter and a negative feedback loop.



    The 5g9 tweed tremolux has all these features except the NFB loop.



    The brown deluxe has all these features plus tremolo
     
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  5. William Pugh

    William Pugh TDPRI Member

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    So then, if the brown deluxe is the Goldilocks of "not too clean, not too grindy, but just right", how close does the pro jr get to that sound (w/o the tremolo, of course)? Or is the tremolo the main attraction of those amps?

    I have NO chance at all of playing any vintage amp (other than a silverface if I'm willing to put out the funds) so I read, really, much too much about this stuff. You guys keep me addicted.
     
  6. E5RSY

    E5RSY Poster Extraordinaire

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    The "Junior" is a bit misleading. I don't think it is the direct descendant of any earlier amp. Definitely tweed-ish, especially with a 12AY7 in V1, even though the EL-84s don't really jive with "tweed".
     
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  7. stefanhotrod

    stefanhotrod Tele-Meister

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    An EL84 couldn‘t generate that typical Fender tone. You‘ve already got a Pro Junior?
    If not, I would highly recommend a little Fender vintage amp: a SF champ or a Vibro champ are still close to the price of a Pro Junior, but they‘re a LOT more amp!
     
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  8. SnidelyWhiplash

    SnidelyWhiplash Friend of Leo's

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    PJs get a bad rap,but i think they are great little amps. :cool:
     
  9. E5RSY

    E5RSY Poster Extraordinaire

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    I don't think that's an accurate statement. What are you calling "typical Fender"? Tweed? Brownface? Blackface/Silverface?
     
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  10. Commodore 64

    Commodore 64 Friend of Leo's

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    My impressions of the Pro Jr are below. Not quite what you asked, I know, but it does give some insight into the circuit. It's a pretty vanilla circuit. It's all about power tube overdrive. I dunno what Fender circuit that makes it like, but it sure as heck ain't no Marshall derivative with layered gain, and cold clipping and cathode follower stages.

    https://www.tdpri.com/threads/wanted-opinions-on-fender-pro-jr.776978/page-4#post-7984227

    So those saying the Pro Jr. needs to be cranked to sound good, this makes some sense. If you look at the circuit (pre-1998), it doesn't have goo-gobs of gain in the preamp. It's not preamp clipping much, and it's designed that way. Neither of the first 2 triodes are bypassed, and both are biased the same (1.5k cathode resistor). That's a pretty vanilla tone heading out to the PI. Anything under 4V out of the pre isn't going to clip much in the PI, either. (PI gain ~26, 26*4 = 104. PI Tube probably clips at ~90V). EL84s biased at about -10.8V, so 21.6V peak to peak max signal before clipping to to feed the power tubes, in that amp.

    SO tone is going to be pretty linear (like a transistor) until you get to a certain point on the dial, and isn't going to get even/odd harmonics until we crank it a bit. Sweetness (or even/odd harmonics) isn't really being generated in the pre, it has to be generated by overdriving the power tubes, I believe it's commonly held that 5V is needed to fully drive an EL84 to max volume. So you've got to be a fair bit over that (I'm little fuzzy on power tube clipping/overdrive) to start getting some hair on the tone.

    So, this is also why the narrative of diming the Pro Jr (both knobs), and using the guitar volume control is so popular. It will allow you to eek out any preamp distortion you can get by running the pre with the least attenuation possible from the pots on the amp.

    This is also why the Pro jr. is such a compelling circuit, IMHO. Not much between the guitar and tubes. It's a very simple, lightweight tube amp. Doesn't break the bank OR the back. If you want some simple preamp distortion, a simple boost pedal can get you there. Or maybe even a hard strum is enough.

    If you want big, fuzzy sound, a pedal sending a lot of square waves can sound good, too, once it's been smoothed out by the softer clip of the preamp tubes. If you are into Marshall-layered, preamp gain stage tone, you aren't going to dig the Pro Jr. You just aren't...Unless you feed it with a signal from a pedal that approximates it. <--and luckily there's about 6,723 dirt pedals on the market you can try (and still not get there, maybe).
     
    Last edited: Aug 19, 2019
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  11. schmee

    schmee Poster Extraordinaire

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    I agree. The EL84 in whatever flavor isn't typical of Fender tone. It's a unique tone with a bit of "szzzzzz" on the top end, and punchy low mids, whether you are playing a Z Ghia, Z Maserati, Classic 30, Blues Jr, Monopprice 15, Delta Blues or Pro jr etc.
     
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  12. stefanhotrod

    stefanhotrod Tele-Meister

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    sorry
     
  13. tery

    tery Poster Extraordinaire Silver Supporter

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    I don't know what the Pro Jr does … but it works :cool:
     
  14. stefanhotrod

    stefanhotrod Tele-Meister

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    This

    5BD2C520-198A-4DD4-8FE2-D0F3995A3940.jpeg

    is typical Fender. Tweed, Brownface, Blackface/Silverface are all typical Fendertones with their own character. The pureness of a tweed, the rougher brownface tone or the shimmering Blackface/Silverface- they‘re all 100% Fender. A EL84 is a lot more british- not good or bad- with it‘s own characteristic. I never get why Fender went to those Power tubes, on the other hand compare their prices...:)

    The Pro Junior is a nice sounding amp but- to my ears- no Fender vintage tone. Nope.
     
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  15. Luthier Vandros

    Luthier Vandros Tele-Holic Silver Supporter

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    Kind of agree with this. To this day - and it makes no sense when you look at it on paper - the BEST cranked clean channel tone I ever had for Texas-styled blues was a Classic 30 I owned back in 2001.
     
  16. E5RSY

    E5RSY Poster Extraordinaire

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    Good question, and there must be a good reason. I imagine Zinky had his reasons. I would love to know why he made that choice when he could have designed it around any tube he wanted.
     
  17. fendrguitplayr

    fendrguitplayr Poster Extraordinaire

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    I don't really know or care, but they do sound great!
     
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  18. stefanhotrod

    stefanhotrod Tele-Meister

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    But what are we talking about?
    Classic Fender tone or something different? More modern sounds?

    I was referring to Fender vintage tone.
     
  19. Commodore 64

    Commodore 64 Friend of Leo's

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    Everything about the preamp design to me indicates minimizing preamp distortion, maintaining linear behavior. That's be a rather boring amp, IMHO, so perhaps zinky was looking to highlight power tube distortion? If I were going for power tube overdrive in a small amp with readily available, current production tubes, I'd go EL84.

    EL84 also run at lower voltage than a typical 6V6, might be a factor in cost of transformers?

    BTW, looking at Tweed Tremolux circuit, the onlything they have in common is a Volume and Tone knob.

    https://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-Pro-Junior-Schematic.pdf

    http://www.thevintagesound.com/ffg/schem/tremolux_5e9-a_schem.gif
     
    Last edited: Aug 19, 2019
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  20. maxvintage

    maxvintage Friend of Leo's

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    I love the pro junior, although i made a pine 12 inch cab for mine. It gets fizzy if you have the volume low and the guitar volume high; it works better with the amp volume hig and the guitar volume backed off. As mentioned it seems to be all about hitting the power tubes hard. It's "tweed-like" in that it doesn't have the blackface/silverface mid scoop, but it has tighter bass.
     
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