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700RB problems

Discussion in 'Amps and Cabs [BG]' started by Montgoda19, Aug 20, 2012.


  1. Montgoda19

    Montgoda19

    Jun 6, 2011
    Pittsburgh
    Well i turned on my head for practice the other day and It started to smell really weird like electrical. Then white smoke started to come out of the lid! I did some research and found that the culprit is the resistors. Now heres a picture but i can tell the color bands on them nor can I find any schematics on the head but as you can see its is slow r73 and r74. does anyone know the right resistors i should replace them with, i work at radioshack so i can pick them up right away! but here is a picture! http://i.imgur.com/sB5Xf.jpg
     
  2. craig.p

    craig.p

    Sep 28, 2008
    New Hampshire
    Don't bother. I suspect those resistors aren't the problem, they're just involved in the circuit where the problem lies, and the real problem is a shorted output stage due to one or more failed output transistors. But that's just a guess.

    Also, you'll need to repair any burned board traces that were smoked by the heat.
     
  3. craig.p

    craig.p

    Sep 28, 2008
    New Hampshire
    One more thought: That amp's fan is functional, yes? And if the amp is racked, it's racked in a responsible manner?
     
  4. john m

    john m Supporting Member

    Jan 15, 2006
    +100

    The resistors did not cause the problem, they took the hit.

    Lots of bass? High gain? Poor cooling?
     
  5. Balog

    Balog

    Mar 19, 2009
    Mukilteo, WA
    I recently picked up a 700rbii that was pulled from a combo. The fan on the heatsink doesn't start running when you turn it on, is this normal? Not sure if it has an always on fan or if it responds to heat load?
     
  6. craig.p

    craig.p

    Sep 28, 2008
    New Hampshire
    Normal. The fan will begin spinning based on amp load and (to a lesser extent) ambient temperature.
     
  7. Balog

    Balog

    Mar 19, 2009
    Mukilteo, WA
    Awesome. :) Now I just need to find a time to crank it up enough to get the fan to go.
     
  8. Bassist4Eris

    Bassist4Eris Frat-Pack Sympathizer

    I'm normally a big GK fan, and was considering a 700RB recently, but a lot (and I mean a LOT) of online user reviews are reporting similar problems to OP's. I fear the 700RB may be a lemon.
     
  9. I totally disagree with this statement - but out of curiosity what amp do you have now and what amp are you now considering?
     
  10. Bassist4Eris

    Bassist4Eris Frat-Pack Sympathizer

    I had an ancient 400rb. It was cutting out, so I took it in for repair, but was considering a replacement. They had a used 700rb, but because of the online reviews, I balked. I actually picked up another 400rb. It's plenty loud for my level of gigging (local clubs).
     
  11. will33

    will33

    May 22, 2006
    austin,tx
    The old 700rb (not the II) is many, many years old and did have some problems. It was replaced a long time ago by the 700rb-II, which cured those issues as well as upped the power. Same story with the old 1000rb and the 1001 being made now.

    I've seen guys beat the crap out of older 700rb's with no issues and others with repeat failures. Don't know if it varies by production run or year or what.
     
  12. ok thanks, I’ve used a few GK 400RB amps over the years - great little amps.
     
  13. will33

    will33

    May 22, 2006
    austin,tx
    I would think older models still in use today may not be the problem amps, but, for peace of mind, if i was shopping used now, I'd probably stick to the "II" models. They have the sort of rock-solid reliability you expect from GK.
     
  14. Montgoda19

    Montgoda19

    Jun 6, 2011
    Pittsburgh
    The fan works fine in the amp and yes its rack mounted and i left an empty slot open right above it for proper air movement and i keep the eq cut below 12oclock along with with highmids .
     
  15. JOE EDO

    JOE EDO Supporting Member

    Aug 28, 2007
    Central New York
    Smoked 2 of them years ago. Loved the sound but not enough to endure on going failures. Moved on....
     
  16. Montgoda19

    Montgoda19

    Jun 6, 2011
    Pittsburgh
    Well i decided to just get a new head then so I picked up a GK Fusion 550 and wow what a good choice
     

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