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Peavey 2x12 with Fender Bassman 100? URGENT!!!

Discussion in 'Amps and Cabs [BG]' started by goran, Jan 9, 2003.


  1. goran

    goran

    Dec 17, 2002
    Croatia
    Endorsing Artist: Bartolini
    I have a silverface Fender bassman 100 and I'm thinking about buying Peavey bass cab with 2 12" and horn (originally a 412TVX cut in half).

    Thing that concernes me is that my amp can run on 4 ohms, but cabinet's impedance is 8 ohms. How will it affect amp's performance? I know that power will decrease, but how much?

    I guess that I'll have to run amp nearly on maximum of power. Is it good for it?


    Please answer as soon as possible because I have to return it in a few days if I don't buy it.
     
  2. From what I've heard, running a 4ohm head into an 8 ohm cab will only give about 50-60% of the output it would give into 4ohms.
    As for running the amp all the way up, it shouldn't really hurt the amp too much unless it gets really hot or starts to clip. If it starts clipping you can damage your amp aswell as your speakers. If I were you I would get a used head with more power of just shell out the money for a head with more power so you have some headroom to work with. It will make your amp last longer and your tone should be better. Hope this helps...
    -Bill
     
  3. goran

    goran

    Dec 17, 2002
    Croatia
    Endorsing Artist: Bartolini
    I noticed that I have to set both master and volume on almost 9 to achieve enough volume. Hope It won't overheat...
     
  4. CraigV

    CraigV

    Jan 8, 2002
    Sounds like this isn't the cabinet for you. There are plenty of great 4ohm cabinets out there. Why not just wait and find one of them?
     
  5. goran

    goran

    Dec 17, 2002
    Croatia
    Endorsing Artist: Bartolini
    Problem is that where I live there is not much bass cabinets available, especially for that price (abot 250$, and new 412TVX is about 1000$, here in Croatia). If I don't take this one, I will probably have to wait maybe a month or two until something shows up. And I need it now.

    Such a pitty. Wish I had more money... Anyway thanks for any advice
     
  6. CraigV

    CraigV

    Jan 8, 2002
    You know, I was just thinking (rare, I know), are you sure the Bassman is rated 100w at 4ohms? I was under the impression that all of the old Fender amps were rated at 8ohms. Most tube amps won't reduce output at all into any impedance for which they are rated. Your volume problem could just be that the cab is very inefficient, or maybe the amp's got tube problems???
     
  7. zoran

    zoran

    May 10, 2002
    croatia
    You can try call Dino at 01/3025588. He can get to you ashdown cabs for 500-600€. Or Music shop 01/6155766, they have good deal with Eden (I don't know how it works after factory is selling) and Ampeg, but if they don't have anything on stock you have to wait for 2-3 months for delivering.
     
  8. Zoran and Goran.
    That's so cool.:D
     
  9. zoran

    zoran

    May 10, 2002
    croatia
    Yes, in our country every bassist name finish with ...oran. According to state law;)
     
  10. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    I've heard this too, can anybody confirm it? Do vintage tube amps really not care about ohmage (as long as it is above the rating)?

    For $250, can't you get an Avatar? A peavey cut in half doesn't sound too cool to me.
     
  11. Not exactly. Tube amps want to see exactly what they are asking for - in the Bassman 100 case, 4 ohms is all it wants to see.

    An old Ampeg V4-B has a switch that let's you choose 2, 4, or 8 ohms. Marshall tube amps are good for 8 or 16 ohms. Most tube amps have multiple output impedance taps of some sort, although a lot of times they are invisibly switched when you use the "Extra" speaker jack. I prefer a switch so I can set it myself.

    The neat part is that a tube amp will put out full power into any of its selectable impedances. The Ampeg V4-B will put out 100 Watts into 2, 4, or 8 ohms. A newer Marshall 100 Watt tube head will put out 100 Watts into 16 ohms or 8 ohms.

    Tube amps aren't like solid state amps where you get the highest power with the lowest rated load. The output transformer is used in a tube amp to match the speaker impedance to the tube impedance, and by using multiple taps on the output transformer it's possible to make the amp capable of driving many different loads to full power.

    Chris
     
  12. Another thing about tube amps that is backward from common knowledge of ss is that if you use a higher impedance than the output calls for you risk damaging your amp. The higher impedance causes a rise in plate voltage and your bias current may become insufficent to keep the amp out of runaway.

    You can go LOWER impedance with power loss but no damage, but when you start raising the impedance across the secondary(speaker output) of the OT, your plate voltage can get dangerously high. Running an 8 ohm cab off a four ohm tap is riding the line. Typically most tube amps don't get too picky until you go over a 100% impedance mismatch, (which is what 8ohms into 4ohms is) but I wouldn't use an 8 ohm cab off a 4 ohm tap; it's a good way to toast a set of output tubes, especially with bass notes generating larger amounts of plate current than guitar does.
     
  13. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    So if my amp has both 8 and 4 ohm jacks, can I use them both at the same time?

    I just reread and saw that Goran is overseas - Avatar probably doesn't ship there. :(
     
  14. Nope. Just use (1) of the taps feeding the appropriate load.

    Chris
     
  15. goran

    goran

    Dec 17, 2002
    Croatia
    Endorsing Artist: Bartolini
    For what I know, running a 4ohm amp with 8ohm cabinet can't really hurt amp (if I don't put everything on 10 ;) ), at least not a solid state one.

    This is the first time that I hear that tube amp don't tolerate more then 200% of their classified impedance. I'm quite sure that I shouldn't use 4ohm amp with 2ohm cab or sth like it. Anyway, I'll try with something else.
     
  16. Ohh! Can I be the third member....moron?
     
  17. You're not dealing with a solid state amp. The rules governing how the outputs should be run are different.

    Going lower than rated impedance with a tube amp will result in LOWER power. The plate voltage is drawn into the core of the output transformer by the lower than expected secondary impedance. The core saturates, heats up, and the plate voltage drops. This makes the tubes themselves put out less power. It doesn't hurt the amp, but you do lose power.