Rivera Fender Concert mods

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by doc, Feb 18, 2005.

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  1. Bigbud

    Bigbud Member

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    You can also replace the 6L6 with KT-77 tubes, which have the same pin-out as 6L6s and EL-34 tonal characteristics. Biasing required though.
     
  2. John Phillips

    John Phillips Member

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    Yes, most likely. It's worse than just fixed-bias too (from this point of view) - it's non-adjustable fixed bias... the Output Tubes Matching control is for balance, not overall bias.

    It's a fairly easy mod for a tech though, and worth doing if you have to adjust it anyway, which involves changing a fixed resistor, so you may as well make it adjustable.

    Fender's logic was correct at the time though, since their tubes were close enough to the spec that they didn't bother with matched sets, and it was better to be able to balance them. Now it's the other way round - tubes vary widely but it's easy to buy matched ones, so an overall bias adjuster is more useful.
     
  3. cestlamort

    cestlamort Member

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    Thanks for the insight!
     
  4. Fuchsaudio

    Fuchsaudio Member

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    I agree with John Philips (sort-of, lol).

    If your tech is adding a second control, instead of bias/balance, I would make it bias/bias. Add a 1-ohm resistor to each power tube cathode, and set the amp up so each tube can be set optimally. Very easy to wire up, and worth doing.

    It's something I could never understand was often overlooked in (most) guitar amps, yet pretty much a given in audiophile tube stuff.
     
  5. bosstone

    bosstone Member

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    That would be certainly be worth looking into. He has a whole kit and DVD for that conversion and that guy really knows how to make an amp sound great.
     
  6. drwx

    drwx Member

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    can anyone fill me in on how hard it is to blackface ch1? maybe a schematic or directions or something.

    i'm going to do the donnyjaguar tonestack mod sometime this week.
     
  7. lostcause

    lostcause Member

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    Hey every one. Newb here.
    Ive actually been following this thread for a long time. Ive had a concert II for about 14 yrs,gigged with it for a lot of that time. Always used pedals for gain.
    The only mods Ive done to it are very recent and include thd yellow jackets and changing out the original speaker for a celestion greenback.
    I could have saved a lot of money if I had done this sooner instead of buying other amps.
    My question is this; What sort of tones are you getting from the amp now that you've done the donnyjaguar mod? What style of music is the gain suited to?
    Thanks guys
     
  8. lostcause

    lostcause Member

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    Ive never done this before....... but....... bump :rolleyes:
     
  9. drwx

    drwx Member

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    i've yet to do the donnyjaguar mod. i really want to get a new speaker first. i'm waiting on corner music to get in the speaker that i want, eminence red white and blue. after that, i will switch out some of the ****** mesa preamp tubes that the guy that had this amp before me had put into it. i've had this amp since the week after christmas...still discovering what it needs and doesn't need.

    there are so many different sounds you can get out of ch2. if i like it after i switch the speaker (it currently has a cbs fender 12f, that's all it says on it) and switch the preamp tubes to some that don't suck, i will decide on if i want to do any mods.
     
  10. lostcause

    lostcause Member

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    I just like the sound of the mod......."The donny jaguar mod".
    If a mod ever gets named after me it wont sound like such a good idea.. "the lost cause fiasco":jo
     
  11. tlpruitt

    tlpruitt Member

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    I have seen both the Torres mod and the Lee Jackson mod for the Concert.

    The Torres mods are actually pretty good and it kinda transforms the circuit into a Dumble like circuit (5uf caps and 1.8k resistors on the cathodes, 150k resistors on the plates, replace the 3M gain pot wired as a variable resistor with I think a 250K pot wired as a voltage divider, and a few other changes). The Torres kit also includes an optional post PI master volume control.

    The Lee Jackson mod involves moving the reverb control to a different location and replacing the wire going to the reverb control with a shielded wire and then putting a rotary switch in the hole where the reverb was that changes the value of the cap connecting V2A and V4A.

    I agree that the Rivera Concert needs a good speaker. I have good experience with a Weber California in the Concert. The Emi Red, White and Blues is probably a good choice too. EV and JBL were the premium speaker choices when these amps were new.
     
  12. Shinequwa

    Shinequwa Member

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    Has anybody here tried an extension cabinet with this amp? I'm looking at both 1x12 and 2x12 cabinets, but not sure which direction I should go as far as size, speaker choices, and open/closed back. Any advice?
     
  13. lostcause

    lostcause Member

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    Ive run it with a 212 cab loaded with v30's and a 212 loaded with G12 ms. Both cabs can be open or closed backs. I like both cabs better either way than the stock speaker it came with. Ive changed out the speaker for a G12m. I like it.
    The g12m is only a25 watt speaker tho and the amp is rated at 60 watts. I run my concert with THD yellow jackets which reduce the output so I think Im covered.
     
  14. donnyjaguar

    donnyjaguar Member

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    Howdy all. I'm posting an update for my channel two modification of the Fender Concert. It was brutally cold this weekend so I took advantage of it by staying in and trying another modification to my Concert. Basically this is an update on my modification which moves the tone controls from the front to the end of the circuit. The tone controls are fed from a signal off V4 which has a 22k and 82k resistor in series on the plate. The original modification uses the tap point to drive the tone controls. What I tried was feeding the tone controls directly from the plate itself. The result is basically the same but now the volume levels are more closely matched. I know at least five people from here have done the modification so I thought I'd mention. I'll update my schematic when I get a chance but just thought I'd share in case someone was about to start into the mod.

    DJ
     
  15. donnyjaguar

    donnyjaguar Member

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    As promised, I finally got around to updating the modification schematic. Click on this LINK to see the image.

    DJ
     
  16. burnydee

    burnydee Member

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    Hi all,

    I've just purchased an 82 Concert II yesterday (in Australia!) and have been avidly reading everything I can find on the net about it. Thanks everyone for your highly informative posts, although because I'm not a technician, a lot of it has gone over my head :)

    I have a question about the reverb in these amps though. The reverb on mine, when set on 10, can barely be heard. I'm all for subtle reverb, but I think there's something wrong here? I do notice that when I turn the reverb knob up, the noise floor / hiss also increases noticeably.

    Could it be a bad tube?

    Also, I have a spare Eminence Red Fang speaker. Do you guys think it would be worth swapping the stock Fender unit out for the RF? Of course, I'm going to try it anyway, hehe, but I was just wondering if you have any opinions on this speaker swap.

    Thanks and regards,
    Daryl
     
  17. jay42

    jay42 Member

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    Something is very wrong with your reverb. It could be V3, V5, or some other problem. If you swap V3 and V7 and it sort takes the whole amp out, you should buy a fresh 12at7. V6 represents a spare 12ax7, as long as you aren't using the effects loop.

    The stock Fender speaker must die :Devil If you end up with a 4 hole speaker like a Celestion, the speaker lugs are removable from the front. They are reverse threaded. You'll also find that the cabinet was built for castors. The major holes are already under the tolex.
     
  18. donnyjaguar

    donnyjaguar Member

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    Agreed on checking the 12AT7 tube driving the reverb. Check also that the reverb is not plugged in backwards. :) With it set to 10, it should be dripping in reverb. People always **** all over the stock speakers but mine sound fine, and not just by my reckoning. Agreed on the castors, I've installed a set. Speakers mount through the back on my cabinet, no need to remove the baffle anchors.

    The best modification you can do to that amplifier is *mine* :)

    YMMV
     
  19. burnydee

    burnydee Member

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    Thanks guys, your advice is most helpful :) I'll definitely check the tubes and let you know how I go. Pre-drilled holes for wheels could most certainly come in handy because I'm amazed at how heavy this baby is!

    Speaker wise, the guy who sold it to me swears it's a JBL, but labeled as Fender. Any idea if that was the case or is he lying through his teeth?

    DJ - hehe your mod is on my list of priorities already :) I'll give myself some time to get used to the amp first.

    Cheers,
    Daryl
     
  20. donnyjaguar

    donnyjaguar Member

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    Take a picture of the back of the speaker and post here. You can tell who made it by the codes on the basket.

    Just ribbin' y'all about my modification. I'm just so happy about it I don't miss an opportunity to extol the virtues. :)
     
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