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removing tubes

Discussion in 'Amps and Cabs [BG]' started by Dutch, Jul 24, 2002.


  1. A sound guy told me the other day that it's quite common to remove one (or more) tubes from a guitar amp to get an overdriven sound (sounds kinda logical to me since you're stressing the remaining tubes). Does this work the same way for Bass amps or will I fry the amp or something? And if so, does it matter which one is removed (there are three 12ax7's in my SVT-IIp)?
     
  2. PICK

    PICK

    Jan 27, 2002
    Sydney, Australia
    Hopefully you realise that you can get an overdriven sound out of an SVT 2 Pro without removing any tubes.
     
  3. CS

    CS

    Dec 11, 1999
    UK
    Pulling tubes normally refers to power tubes because the owner found out the hard way that the amp is way too overpowered for 99% of the situations it's used in.

    What you do is remove the outer 2 and adjust the resistance of the speaker cab. All you get is a 3db attenuation which can be achieved by changing speaker cabinets (look at te db numbers on the cabs).

    Removing preamp valves will just make something not work. If you have three ECC83's in an amp with no effects (reverb trem etc) you will probably need them.

    Some players remove the trem circuit valves if they dont use trem like Brian May who runs his AC30s full chat and wants to get the temperature lower.
     
  4. If you remove any of the 12AX7s it won't work at all. Whilst I don't know the amp in question, the usual 12AX7 configuration is #1 and #2 = mix, gain, tone shaping, etc. #3 = phase splitter for the output valves: you need all these in circuit.

    I'm not enough of a valve tech to say exactly what would happen if you removed a pair of output valves (assuming it has at least 2 or more pairs). And it would have to be one valve from each side of the output transformer, not just any old 2 valves.

    However, removing valves would make the HT voltage rise which would increase the static disipation in the remaining output valves. This would be likely to put added strain on those valves and possibly take them outside their max, ratings. Increased HT would put more voltage across capacitors, which they might not like very much :eek: The output and mains transformer may suffer, too.

    If you want the overdriven sound, why not just crank the gain right up?

    John
     
  5. I'm sorry guys, I guess I wasn't clear. I'm talking about an Ampeg SVT-IIp preamp (the predecessor of the SVP-pro. The SVT-IIp has no gain so I was looking for another way to overdrive and I hoped this could do the trick.
    Right now I just set the master of the preamp to maximum and adjust the volume with the (SS) poweramp (= Ampeg AP3350) but it doesn't give me that famous ampeg growl I was hoping for.
    Any suggestions?
     
  6. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany
    I recommend getting a line booster. If you make the input signal hotter, the preamp will distort more.
    This is much easier and safer than messing with the preamp. Also makes it switchable.

    What's the rest of your setup? Bass and cab matter too.
     
  7. CS

    CS

    Dec 11, 1999
    UK
    My amp is not an ampeg but it does growl-it has 4 KT88's.

    re the line boosters if you have the cash look into the SHO by Zachary Vex and the Fatboost by Mike Fuller

    http://www.fulltone.com
    http://www.zvex.com

    both gentelmen will answer questions but Mike Fuller has been reported as being ''short' (although he has been nice to me) zvex has an Q and A on the forum on his site.
     
  8. a Line Booster? Never heard of those before. Is that some kind of a stomp box that does the same as active pickups do?

    My bass is a Japanese Fender Precision and I have an Ampeg 1x15 and a Trace 2x10 cab.
     
  9. Golem II

    Golem II

    Jan 4, 2002
    Macon, GA, USA
    How about a simple distortion pedal?
     
  10. jokerjkny

    jokerjkny

    Jan 19, 2002
    NY / NJ / PA
    IMHO,

    i dont think a SHO or Fat Boost would really give you that grind. they're only clean boosts. i wouldnt go as far as say they're "line boosters" perse. you'd still have to crank the pedal pretty hard to achieve any extra clipping, all the while blowing out your speakers from the mind numbing volume.

    if you're willing to drop on a pedal, like Golem said, just get a Sansamp BADI, or Fulltone BassDrive for simplicity sake.
     
  11. Paul A

    Paul A

    Dec 13, 1999
    Hertfordshire U.K!
    Build One!
    They are SO easy the EH LPB1 or 2 (linear power booster) works great for bass OR the "Hogs Foot" which I beleive was a bass booster.
    Heres the schematics:
    :D
     
  12. Thanks a lot to all of you for all the input!! Upon reading all of your posts I think that the clean gain boost probably comes closest to what I am trying to get. I don't want to distort the signal, just a 'slight' grind or growl (i.e. Matt Freeman) is what I'm looking for.