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taming the reverb question, DRRI

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by cbnutt, May 18, 2011.

  1. cbnutt

    cbnutt Member

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    i recently picked up a DRRI as a back up to keep around if my old SFDR quits in the middle of a gig, anyway, when i first looked at it in the store the reverb didnt work, so they said before i bought it, they would order a new pan, problem is it seems to get wayyyyyyyy to much reverb very quickly when just starting to turn up the knob, so i remembered on my old silverface that i put in a 12U7 tube, and it tamed it down tremendously, very easy to control, even turning up high, so on the DRRI i did the same with a 12U7, but,, it still seems to have almost as much as before, just cracking the knob up to about 2 or more is like my other amp on 7 or 8, i know the 12U7 tube trick has always worked great in the past on all the amps ive had, so, could the pan be the wrong one for the amp ? or something elese be wrong ?
     
  2. CharlyG

    CharlyG Play It Forward

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    Don't know about those tubes, but I put a 12AT7 or 12AY7 in my Fenders for reverb.
     
  3. wizard333

    wizard333 Member

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    12AU7 would be the thing I'd suggest. 12AT7 is the stock tube which is much hotter, 12AY7 is the wrong tube for that application; its a low gain tube like a 12AU7 but a reverb circuit needs the high current of a 12AU or 12AT.

    Since the 12AU7 didn't work to tame it, you could try a different pot. Stock is 100k Linear, you could try 50k Linear or even 25k linear and see if you like that better.
     
  4. RussB

    RussB low rent hobbyist Silver Supporting Member

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    Perhaps the replacement reverb pan wasn't the proper unit?
     
  5. cbnutt

    cbnutt Member

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    yes 12AT7 is normal, but a 12U7 will usualy drasticly reduce reverb, its basicly a very weak tube, but in this case didnt do much, the pot thing might be right ? are the pots differant in the DRRI compared to a older silverface ?
     
  6. wizard333

    wizard333 Member

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    The pots are physically different. New ones are pcb mounted. But the values should be the same.

    Its highly unlikely it was a wrong tank; if it were, it either 1) wouldnt work at all, 2) would be weak, 3) would hum badly due to impedance mismatch. It wouldn't be too strong.
     
  7. cbnutt

    cbnutt Member

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    yea i wandered about that , dindnt know how much that can affect he amount of reverb.
     
  8. CharlyG

    CharlyG Play It Forward

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    Yer right, I put the 12AY7 in V2......I "mispoke"! {;^)
     
  9. cbnutt

    cbnutt Member

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    i was thinking several years ago i had done the 12U7 thing in another DRRI i use to own and it cut it down alot, and its diffantly way down and managable in my silverface. if i remember corectly for referance, i read that a 12ax7 is ratted at 100, and the 12U7 is only like 15 or 20 ? diffantly a weaker tube .
     
  10. RussB

    RussB low rent hobbyist Silver Supporting Member

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    Take out the reverb tank and post the numbers you find on it. It may even be some off-brand.
     
  11. wizard333

    wizard333 Member

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    Forget about u (amplifaction factor) for a second. In a reverb circuit its best to have a high current driving tube, that means 12AT/12AU family, rather than the 12AX/12AY family. Conversely, in a pre-amp stage, the 12AX/12AY generally sound better as that is what most amps were designed for. The 12AU/AT family biases different ( your pre-amp tubes are cathode biased). So if you are going to sub something for a 12AX, use a 5751 or 12AY. If you are going to sub for 12AT, use a 12AU. You can violate that without the world blowing up, but that will give you the best results.
     

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