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Using the preamp out on an all tube head

Discussion in 'Amps and Cabs [BG]' started by i_got_a_mohawk, Jul 2, 2005.


  1. I was just wondering about this, because i dont think it will bypass the power section, so if you were wanting to use just the preamp out, you would still need a load plugged into the amp :eyebrow:

    So doesnt that make a preamp out on an all tube head pretty useless?

    (probably not, just wondering)
     
  2. You must keep a speaker load on a tube power amp, yes, but the preamp out wasn't designed so you could use the preamp by itself. Since tube bass amps are usually woefully underpowered, the preamp out was put there with the intention of slaving multiple amps together.
     
  3. woefully underpowered?

    anyway, aye, i can see that being a point, multiple poweramps n such
     
  4. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    On some amps I've played, the preamp stage works while the power amp is in standby.
     
  5. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    I knew this all along.
     
  6. Fealach

    Fealach Guest

    Apr 23, 2003
    Gone to a better place

    Is that a comment designed to stir up a @#$%storm, or are you serious about the "underpowered" bit?

    I seem to recall reading in the manual for the dreadfully underpowered Mesa Boogie 400+ that supposedly you could leave the master volume at 0 and use its preamp section without needing a load. I never tried it, it just didn't sound right to me.

    Of course I eventually sold it, it being so anemic and all. I bought KISS's old touring rig from the stadium days, the one that took all those semis to haul around, and filled the stadium. That's almost powerful enough for a bedroom practice amp.
     
  7. Because of the way tubes work im sure you really need a load attached whether the master volume is at 0 or not, i could be wrong tho
     
  8. dood

    dood

    Dec 9, 2004
    sitting down,facingforward..UK
    Endorsements: Shuker Guitars, Dingwall Designer Guitars, D'Addario, Planet Waves, Barefaced Bass
    yea, you must keep any valve poweramp loaded, even if the volume is down. However, I have heard that you can get/make dummy loads or use a similar 'power break' product to plug in instead of a cab so the amp is loaded but negates the need for a cab.
     
  9. yeah, i started a thread on it, seems to be more hassle than i can be bothered to do really
     
  10. dood

    dood

    Dec 9, 2004
    sitting down,facingforward..UK
    Endorsements: Shuker Guitars, Dingwall Designer Guitars, D'Addario, Planet Waves, Barefaced Bass
    ;o)


    no surprise there then LOL. I'm not sure how many manufacturers make powerbreaks etc.. and I'm sure there must be reasons why resistors hanging off the back of the amp aint to great!! lol
     
  11. oi!

    Probably because all 300 watts of energy going to the resistor is released as heat?

    And id imagine it could get pretty toasty :p
     
  12. dood

    dood

    Dec 9, 2004
    sitting down,facingforward..UK
    Endorsements: Shuker Guitars, Dingwall Designer Guitars, D'Addario, Planet Waves, Barefaced Bass
    ;o) that wasnt aimed directly at you, lol, more that i certainly would bother running around trying to find out whats right and not for building a load for *my* svt amp.

    Yeah, I gues you could set up a mini grill with the heat coming off one of them!!


    heh heh.. I could just see my singer nipping round the back of my bass cab to have a quick burger whilst we go off on a 20 minute self endulgent widdle fest he he he
     
  13. Yeah I'm serious. That's my opinion and I'm sticking to it. 300 watts isn't much by today's standards and you'll be hard pressed to find a tube amp much bigger than 300 watts. I'm an ex-SVT owner myself and I used to run short on power quite frequently.
     
  14. 8mmOD

    8mmOD

    Mar 20, 2005
    USA
    I endorse & use Tech 21 pedals, Eminence loaded cabs, EMG pickups, Jim Dunlop picks & Ernie Ball Strings, BC Rich Basses.
    Wow... then I feel bad for the guitar players and their little 100 watt tube amps. :meh:
     
  15. Fair enough if you feel that way, but 300 watts of tube power can go alot louder than 300 watts SS

    And i know for a fact that there is a 600 watt all tube head, its only 10 grand :bag:
     

  16. It's not strictly necessary unless there's signal passing through the OT. If your amp has a master and you keep it all the way down, there isn't much chance of damaging anything. However, I'd generally reccommend connecting an appropriate load all the time.

    Having to have a load on a tube amp doesn't really have much to do with the tubes as much as the output transformer.

    I'm not getting into the whole SS vs tube argument other than to say that I've never had any issue being heard with my SVT.
     
  17. I thought it was always a thing to do more with the output tubes, but ach well, learn something every day :)

    I dont think ill fire up my amp sans a load, i just wouldnt feel comfortable doing that

    Should try and see if the pre works when in standby, and post back results, hopefully without blowing anything up
     

  18. The pre won't work in standby. The only things that would be on in standby are the filaments (heaters), the high voltage supply would be off.

    You can actually design tube amps without output transformers that you can run with no (infinite) load no problem.
     
  19. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    Yes.

    So doesnt that make a preamp out on an all tube head pretty useless?[/QUOTE]

    Well, for use just as a preamp, then yes, an all tube head certainly is not the best choice. But, the ability to slave another amp can sometimes come in handy. I like to mix and match tube and ss amps, so you could slave a good ss amp off of an all tube head. Or, if you just need more tube volume, then you can drive an additional tube power amp.

    Tom.
     
  20. Yeah, it was actually my curiosity to see why the SVT II preamp sounded like through the power section of my peavey

    Yeah, i have too much spare time :p