Rivera Fender Concert mods

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


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  1. doc

    doc Member

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    I finally opened up my Concert II and took out several of the caps bridging the preamp tubes, rearranged a few of the leads, and changed out a couple of tubes, and am very pleased with the results. I now actually like the overdrive (sounds like a Boogie), but the clean channel is not quite to my taste yet. If I can get the clean to sound like a blackface or tweed Fender and the overdrive into Dumble territory I'll quit. I know Dan Torres has a "mod kit" out for this, but I'd rather not blow the $50, and it sounds like his mod is more drastic than I'd like anyway. I really don't like the idea of one master volume for both channels. I also don't think the Jackson mod really does what I want either. I have the schematic but with the switching being somewhat complex I have a hard time following the signal through it in different modes, otherwise I'd make a stab at tweaking the preamp a bit more myself. Any suggestions? If anybody has a copy of either of the above mods they'd like to give some details on I'd be interested - maybe I can incorporate some of what they did. I also don't understand in this amp why Rivera in 2 places ties both sides of a 12AX7 together and runs signal through both as if its one gain stage - it seems he wastes a whole tube that way. (and he DOES waste half a preamp tube later)
    I know I was advised to leave the amp alone, but I'm an inverterate tinkerer and couldn't help myself. I now plan to try rearranging the overdrive preamp tube component values to more "Dumblelike" specs and am considering using the unused half of tube to give one more gain stage in the overdrive mode. I'm also thinking I'll change most of the preamp to metal film resistors and solid core wire. The problem I think I'll run into is that the amp is fairly complicated, and I'll probably run into noise and oscillation problems as I proceed. I might be better off to simply put the caps back in, sell it and buy a Two Rock or Fuchs later (but I'm also a cheapskate). Any thoughts?
     
  2. John Phillips

    John Phillips Member

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    The single biggest improvement you can make to that amp - by far - is to ditch the stock Eminence speaker (if that's what it's got, still) and fit something much better. The stock speaker is harsh, flat and farty all at the same time - which is quite an achievement ;) - and especially doesn't like being really pushed. It doesn't sound great (I would say quite sterile) on the clean channel, but is even worse on the dirty one.

    I would highly recommend a Celestion G12-65 for a 'RF'-type blues tone, or possibly a G12K-85, which I think is what Rivera uses in some of his current amps, for a heavier sound. I've fitted quite a few of them with 65s, and only one so far with the 85, which I just had lying around, but was quite impressed.

    BTW, if you're in there anyway, check that the 47-ohm 1/2W carbon-comp resistor on the tag strip next to the transformer has been replaced with a 1W metal-film or wirewound. It's in the bias supply, and they have a nasty habit of failing and blowing the power tubes.

    Other than that, I'd leave the circuit alone actually...
     
  3. hawkeyeinexile

    hawkeyeinexile Silver Supporting Member

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    i've still got my '82 head. do you have the original (or replacement original) power tubes? that would be key to the clean sound, i'd guess. also to getting the full output. they were Syvania STRs (357? 387? i forget, am using svets right now)

    :cool:
     
  4. doc

    doc Member

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    Thanks for the suggestions. I did already replace the speaker with a Celestion and did note a significant improvement. I'll have to check on the resistor next time I'm in there as I put it back together after my first foray, but I'll definitely look at it.
     
  5. Jon Silberman

    Jon Silberman 10Q Jerry & Dickey Gold Supporting Member

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    Keithrick, welcome to the board. :)
     
  6. vbjamin

    vbjamin Member

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    I put Groovetube Substitubes in my Rivera Concert head and it burnt up, literally!. Groovetube is going to cover the repair, but it has sat at the shop since December 04 as Fender sends the parts one at a time. Sounded great for 10 minutes.
     
  7. Radax

    Radax Member

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    Stock tubes but I switched to a EVM 12L. Good move.

    Mike
     
  8. vbjamin

    vbjamin Member

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    Whoa Happy happy Days!! Got my Concert Back, retubed, new caps, NOS AU7 in V2 and Groove tube Substitubes 2 x EL84. WOW IT SOUNDS GOOD! No buzzy gain, rich detailed clean and I can crank it tot 10 and not blow the windows out. So happy, can,t wait to gig with it
     
  9. darkbluemurder

    darkbluemurder Member

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    I also have a Rivera era Concert. Great amps because they have the same output transformer as the blackface Bassman.

    I use a Jensen NeoDym 12''. Great match for this amp. To brighten the clean sound, just remove the plate to cathode caps in the preamp, remove the 820k resistor between the tone stack and the clean channel volume and rewire the bright switch to blackface Fender. This is a very good starting point. I am still experimenting with the driver circuit - I already raised the PI output coupling caps from 0.01 to 0.1 uF. The effect wasn't too noticeable. I will probably increase the grid loads in the PI from 330k to 1M and reduce the FB resistor as well to increase the bass more.
     
  10. stratopastor

    stratopastor Member

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    I collect Rivera-era Fender serial numbers (it's a long story and I don't want your pity). Let me know your amp's serial number and I'll date it for you. If you tell me the transformer date codes (606-xxx) it'll sharpen the picture for the next guys...

    cheers

    SP
     
  11. hawkeyeinexile

    hawkeyeinexile Silver Supporting Member

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    this one is F415340

    :cool:
     
  12. stratopastor

    stratopastor Member

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    Jeff, yours comes from the last batch they made - '84 or '85 - info is a little scanty...

    best wishes

    SP
     
  13. hawkeyeinexile

    hawkeyeinexile Silver Supporting Member

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    thanks, SP. i really like these amps. have had 4 of them. one sold, one mod'd by Andy Fuchs, one traded (a 4x10) (in part) for a Rivera S120, and one left.


    :cool:
     
  14. TheAmpNerd

    TheAmpNerd Member

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    Hey SP, would that include the Fender Concert
    amp from say 78 - 83?

    I just serviced on of these for harp player.
    He had 2 x 12 Alnico version.

    Do most folks consider these 78-83 amps Concert IIs?
    Even though some of these just say Concert
    on their faceplates.

    Of course neither of these should be confused
    with the Brown Face concert amps.

    Now I'm wondering.
     
  15. stratopastor

    stratopastor Member

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    Nerd, the Rivera-era Concert was made '82-86ish, and has serial numbers beginning F2, F3 or F4. It's popularly called the Concert II because that WOULD HAVE made sense, as most of the other amps in the range were also IIs. However it's officially called the Concert, just like all the other Concerts that came before it, even though it was a completely new design. Hey ho.
     
  16. Jon Silberman

    Jon Silberman 10Q Jerry & Dickey Gold Supporting Member

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    I sold the Rivera Concert I bought NOS in '87 in '95. It was one of the ones with the stock EV. It was just too damn heavy.
     
  17. darkbluemurder

    darkbluemurder Member

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    The comments about "Concert II" are correct - that would have been the most logical way to name these amps.

    The only downside my amp has is that the power transformer gets very hot and stays hot even after the amp is switched off and the power tubes have cooled down. Since none of my other amps have this I cannot accept this as "normal".

    Has anyone experienced a similar problem with these amps and what can be done (besides adding a cooling fan)?

    Any input would be very much appreciated.
     
  18. donnyjaguar

    donnyjaguar Member

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    Howdy all,

    I just found this forum and although some of the postings are a little old I'm hoping there are still folks listening. I'm in the process of fixing up my Fender Concert amplifier and can probably add some value to others doing the same thing. I've been running the amplifier on EL34 tubes for years. Why? I just like EL34s because they are a true power pentode and not a beam-deflecting type. And besides, most of my other gear uses EL34(6CA7) so I have plenty of spares. They work perfectly fine and the amplifier has lots of grunt. Soundwise is still certainly sounds like a Fender.

    I'll write more later if there is interest.

    FD
     
  19. vbjamin

    vbjamin Member

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    Did you just slap the EL34 in, in place of the 6l6's,OR DID YOU HAVE TO DO ANY OTHER MODES TO MAKE THAT COMBO WORK? if so I am going to try this.
    I am currently using an AX7 IN VI, AN au7 in V2, an at7 IN V3 with JJ EL84s in GT Substitubes in place of the 6l6s.
     
  20. deeval

    deeval Supporting Member

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    Did you have to rebias since there is no bias pot just a matching pot did you change the bias resistor,and anything else did you mod?:D
     
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