Rivera Fender Concert mods

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

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  1. donnyjaguar

    donnyjaguar Member

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    This is probably a safe swap now that I think of it. The cathode resisotrs are 82k & 100k in most cases and with more than 13k on the cathode there isn't the opportunity for much current to flow in this section of the amplifier anyway. I'll have to try this myself. :) I'm guessing the difference in tone will be more apparent with the neg feedback reduced (or eliminated).

    DJ
     
  2. darkbluemurder

    darkbluemurder Member

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    What I recently did to my Concert was to put it back into its head enclosure, increase the PI coupling caps to 0.1uF and the grid loads from 330k to 1M. The amp sounds way fatter now :)

    With the OD channel I tried something different. I changed Rk/Ck of V2b from 1k5/25uF to 10k. This decreases gain somewhat but the sound is less muddy and more touch responsive. However the amp needs to be turned up quite a bit for full effect. Haven't tried it with the band yet.
     
  3. donnyjaguar

    donnyjaguar Member

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    Interesting on the coupling caps & bias resistors. My Concert II sounds so thick already I didn't bother modding this part of the circuit when I did my latest mod's. I will however experiment the next time I have it apart for a checkup. :)

    As for modding V2B, the only danger I see here is you won't have enough volume when cranked. :( If you put a 22uF across the kathode resistor in V5a it'll bring the gain (and noise) up quite a bit.
     
  4. darkbluemurder

    darkbluemurder Member

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    Good point on V5a, I added the cap because almost every 60s BF and 70s SF has it. Hiss did increase slightly but not in an objectionable way - perhaps I am not too sensitive to hiss - I certainly am to hum or buzz).

    I can assure you that even after the mods to V2b the amp is still plenty loud - I need to keep the attentuator set very low to try this at home. My favorite OD channel setting with the mod is Vol. 4, Gain 10, Master 10, Treble 8, Mid 8 and Bass 6-7.
     
  5. donnyjaguar

    donnyjaguar Member

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    Nice. Now the problem with my Concert is if I put your tone settings the same it's gonna sound different. I re-configured the 2nd channel moving the tone stack from the input further down to the output. This is a worthwhile modification as it gives much more crunch and much better control over the resultant tone. That is if you're going for crunch of course.

    I also replaced the 2x 4uF cap's with 33uF ones. My math could be wrong, but I calculated that the optimum value is more than twice that. The 33uF were handy (and good for 350V) so I put them in. I did so many other mod's at the same time I can't say for sure if they made much of a difference though.

    I can upload my modded schematic to my FTP site if you or anyone else is interested.

    DJ
     
  6. vbjamin

    vbjamin Member

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    [​IMG]
    My Concert, New caps, Svetlana 6L6,S and 3 prong plug.
    Love to keep her but I want to raise $$ for a Matchless Lightning 15.
    All offers consdered, stock speaker box.
     
  7. EBGB

    EBGB Member

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    Do any of you guys live in or near New York City? I have a mid-80s 60w 1x12 Rivera Concert I might like to mod. Do any of you feel your mods made this a really 1st-rate, no compromises amp? I like mine and have used it since high school but it can be a little sterile, harsh, high freq piercing-- and buzzy mushy on the overdrive.

    Does anyone use ch.2 as their main clean sound? Suggest settings?
     
  8. darkbluemurder

    darkbluemurder Member

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    I am in Germany. I have not yet the Concert in a state that I really could say it's a no compromise amp but I am very happy with my Deluxe Reverb II which I've modded to a *umble style clone. This is really a do-it-all amp from spanky cleans, clean with a slight grit/drive on 2-2,5 on the gain channel, crunchy from 3-4 on the gain and everything beyond that with smooth sustain. By now there are not many original parts left in that amp except for the power transformer, tube sockets, jacks and some of the pots whereas the Concert is still close to original. I am planning to do a similar mod to the Concert soon.
    I never used ch.2 for clean sounds - you would have to turn down the guitar volume and have a lot of hiss.
     
  9. darkbluemurder

    darkbluemurder Member

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    It's done now - I implemented the *umble architecture into the Lead Channel of my Rivera era Concert. I took the amp to a gig the same day and was very satisfied with the sound. All I am about to do with this amp now is fine tuning - there is still some harshness which I cannot dial out with the knobs.
     
  10. donnyjaguar

    donnyjaguar Member

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    Darkblue, what is this *umble architecture of which you speak? Do you have a schematic to share?

    DJ
     
  11. darkbluemurder

    darkbluemurder Member

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    It is the 1977 schematic - please check www.ampgarage.com under the D Files section.
    BTW the harshness I spoke about was due to high voltage on the plates of the overdrive tube. By swapping two resistors in the power supply (2k2 for 10k and vice versa) I lowered the voltage to that tube and got rid of the harshness. For the *umble circuit the voltages on V1 and V2 are critical - that would be V1, V2 and V5 (or V4?) in a modded Concert.
     
  12. mike.mcglone

    mike.mcglone Member

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    I just swapped a Concert s/n F409529 faulty for a working HotRod with a mate who wanted a reliable amp for gigs and I now intend to repair and restore the Concert for myself but feeling a bit rusty in that I have not worked on amps for years now.

    I believe the unit was one of the first export versions into the UK and has a history of noise, poor sound and blows HT fuses. On inspection all the pre amp tubes where Chinese Golden Dragon 12AX7, including the Reverb and Phase Inverter instead of 12AT7, and a pair of odd sized bottle 6L6GC groove tubes in the output. The mains transformer and possibly the coil looks like it has been a bit hot in its history but other wise the amp looks great. Replaced output tubes with some 80's Fender USA tubes I happened to have and adjusted tube matching pot on scope. Now the amp sounds a lot better however intermittently still blows 500mA fuses - even when replaced briefly with 1amp quick blow whilst investigating - the mains TX does not feel too hot but the amp does not sound very load, especially compared with the Hotrod Deluxe which was only 40W? Tried comparing HotRod cabinet which didn't improve sound or volume.

    I have ordered a new set of HV caps and a matched pair of output valves from TAD Germany - any thoughts? 47ohm in the matching circuit ok but 100k across V6 measures a little high so replacing this. The amp is in immaculate condition with 2 standard - not EV speakers. I also have a Super Champ EV F414283 in mint condition that I picked up in the eighties and a 66 Black Face Super Reverb.
    cabinet which didn't improve sound or volume.

    This looks like a great thread any advice and info welcome, I have purchased the Torres mod but on reflection don't think I will be fitting this...
     
  13. Fuchsaudio

    Fuchsaudio Member

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    The Rivera era Concert is one of the better Fender platforms, like the Fender-75, it has decent iron, a nice high plate voltage, and we have boards and panels all designed for an extremely professional end-product.
     
  14. John Phillips

    John Phillips Member

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    That's quite funny... slightly ignoring the fact that the Concert isn't actually working properly at the moment. But fix it right, and it still will be long after the Hotrod is in a landfill :). They're one of the best-built amps ever, by any maker.

    They do have one particular weak spot though. On the tag strip next to the PT is a 47-ohm, 1/2W carbon-comp resistor that feeds the low-voltage supply for the bias circuit and the switching system. It's not up to the job, and often fails, which leaves you with no bias on the power tubes and will definitely blow HT fuses (and tubes). It can crack, and so become intermittent, rather than failing entirely. Many techs replace it with another 1/2W one, sometimes even carbon... which just delays the problem coming back. Replace it with a 1W (or higher) metal-oxide or wirewound instead, and cure it permanently.

    I'm not sure if this is going to fix all the problems at one go (I'd guess not, from your description) but it's the first place to start.

    You should also check the condition of the 1K5 grid stopper resistors (replace with metal-film ones if there's even the slightest question about them) and the 470-ohm screen grid resistors (replace with 3W or 5W wirewounds), especially if the bias supply resistor has failed, since the tubes will generate a huge amount of heat and cook these resistors even faster than usual.
     
  15. mike.mcglone

    mike.mcglone Member

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    It was the 47 ohm despite measuring ok!
     
  16. mike.mcglone

    mike.mcglone Member

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    Has anyone tried this mod and if so howdoes it sound?

    Thanks
     
  17. epluribus

    epluribus Member

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    Hey SP. Love your website, I've been on it many times. Required reading for us Fender/Rivera fans. FYI, recently I got a phishing warning when I went there, thought you should know.

    As for S/Ns, I have a DR II, an '83 by the S/N, speaker and component codes, etc. As far as I can tell, I'm the first person ever to get inside it, and the cosmetics are very nearly flawless. Needs caps and a bench check, but OEM except for the Weber 12F150 I just stuck in it. Anyhoo, S/N F329529.

    Picked it up in a flea market from a veteran blues guy--thread in itself. Suffice it to say he was an inspiring guy for many reasons, his generosity among them.

    Glad I got a chance to type at ya.

    --Ray

    BTW, for our other readers, there are quite a few Rivera/Fender threads in the archives, tons of good ones, and most seem to be about the Concert. Huge useful to me, my thanks to the contributors--worth checking out for sure!
     
  18. epluribus

    epluribus Member

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    Hey John.

    I just stuck a Weber 12F150 in mine, and I gather from play-testing that it's a much more efficient speaker besides the other mechanical differences. Possibly its greatest asset. (It does break up in a much more articulate way than the Emi, BTW.)

    I played the amp in before the swap, and set both channels up just beyond the point of harshness and low-end flab. Ch. 1 was set for conventional blackface drive, while ch. 2 was set for preamp drive with lots of gain and mid-boost, relatively clean power end. After the swap, the flab and edge were long gone, and the gain structure points on the controls moved considerably. Also, the clean tones seemed to have more richness and roundness, like stronger harmonics or something, which may also be a bennie of better-fed power tubes and OT.

    Anyhoo, my provisional conslusion is that a big part of the improvement is due to the improved efficiency allowing the power supply system to keep up better.

    Incidentally, I've not found efficiency specs on the Webers anywhere--anybody got a good source for speaker specs?

    Opinions?

    --Ray
     
  19. mike.mcglone

    mike.mcglone Member

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    John, my amp is working fine now that I have replaced the 47ohm and the HT caps, what speakers would you consider as a replacement for the 10" units? From what I have read the Eminence units are not as good as others on the market. I saw your note about G12-65, would you recommend the 10" equivalent? Cheers Mike
     
  20. tudor@cavernmus

    tudor@cavernmus Member

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    I've just bought a 2x10 Concert and I too am getting that nagging feeling that the stock Emi units aren't doing it any favours. I too believe a speaker upgrade would be worthwhile, but there's almost too much choice and you can only tell so much by reading the specs and data.

    Does anyone here have any suggestions?
     
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