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Tubes - discuss

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  • Perhaps one of the tube guys can recommend and add a few TOP choices for a few different wattage's of amps. To get the convo rolling.
  • I currently have two tube amp projects started.  I won't be working on them until it's it cold outside.
  • I have a very nice preamp but i am interested in a high quality/value tube preamp. Maybe something I can integrate with one of the class d boards and build a nice wood chassis for it.
  • This is just my opinion, based soley on the tube amps and preamps I have built and listened to:

    DIY tube preamps and smaller wattage tube amp projects are fun and make sense.

    Trying to build a higher wattage tube amp to replace your 100+ wpc Carver, or Adcom, or Rotel, or... doesn't make sense.

    Dollars per watt goes up exponentially with tube gear.  Mostly due to the iron (transformers).  

    And 8 wpc tube amp can be built for a couple hundred and can be great for filling a small room with with wonderful sound using reasonably efficient speakers.  A 30 wpc amp is less than 6 dB louder but would cost much more than a grand.  It would be big and heavy and throw off tons of heat.  No thanks, give me a nice Class D instead.
  • Another thought on tube amps:  the best thing about tube amps is the clarity and natual sound of the mids and highs.  The best at doing that in my opinion is single ended tube (SET) amps which run in pure class A mode.  Because of this 8 to 12 watts per channel is about all you're gonna get unless you start paralleling tubes, which in my estimation would ruin the clarity and natural sound.  Also SET amps aren't the best for controlling woofers and deep bass.

    So with that said I really only see two options to running a SET amp in your main system.  Option 1 (most popular):  use extremely efficeint speakers, like 98 dB or better so you can get loud and not run out of headroom.  Think all pro drivers or line arrays (line arrays... hey Roman ;)  )

    Option 2 (my favorite): go three way active. Use a miniDSP to feed a big solid state amp that drives your woofers.  Then feed a SET amp that drives a passive MT.

    Make sense?
  • Does anyone know anything about the expensive tubes themselves? I was looking at some.. 300B Chinese make that seem to demand hundreds of dollars per pair. Snake oil?
    = Howard Stark: "This is the key to the future. I'm limited by the technology of my time, but one day you'll figure this out."
  • Think that's alot, check out Western Electric NOS B300's.  Thousand or more per pair.  Mostly marketing and people telling themselves they sound that much better.  There are many cases where the cheaper Soviet replicas (like JJ) test better than mega buck NOS. MHO is that the circuit's design and the output transformers have far more influence vs. the brand of tube.  Now do different model of tubes sound different???  Absolutely yes!  An EL84 tube sounds very different than a 6L6.

    If anyone is interested in a small, affordable, DIY SET amp I'm working on a design that is still in the prototype stage.  It'll do an honest 5 wpc for around $250.  That is using high quality components everywhere.  It would make a great desktop or office amp.

    BTW a B300 SET amp could easily cost  $1000+ and be good for only about 3 wpc.
  • I Like option 2... the would make the most sense. and while you are at the DSP, take care of the Bass mid integration, BSC, and any other nasty stuff....

    Why 5 watts? That seems like an odd figure, the most common SET is around 8 watts. How efficient the MT needs to be for 5 watts?
  • It also depends on the size of your room and listening habits.

    I have a pair of Manley Mahi monoblocks that deliver 20w in triode configuration(double in Ultralinear).  For me, they're enough for a high 80db efficiency speaker, but I don't listen at concert levels either.  On a CD and SEOS24, 20 watts could be deafening if need be.

    As for 5 watts or less, IME, it can work well on a small nearfield setup, a large horn, or as mentioned above, possibility on the TM section of an active speaker.  I have a small 2 wpc amp that I can post images of later.
  • Yes very good points Face.  I bet those Manley Mahi monoblocks sound awesome!!!

    Ani, the power rating of 5 wpc on my prototype amp is simply based on the tube's rated plate power dissapation.  The 6V6GT has a max rated plate dissapation of 14 watts.  This rating is pushing the plate voltage to the max rating, and cathode/plate current to max.  Tube life is directly proportional to how close to max ratings you drive them.  Every design is a tradeoff of course.  Because tubes do wear our and die, and the difference between 5 watts and 10 watts is only 3dB I chose to run the tubes at a very easy bias.  They will probably live for 3000 to 5000 hours.
    These 6V6's will be operating in ultralinear mode.  I like how UL sounds, better bass.  In triode mode the amp would only make 2.5 -3 W (spud amp).  Looking closer at my BOM this amp could be built for around $180 if you have a few parts in your bin already like speaker binding posts, a power cord, power switch, etc. The actual tubes and iron aren't terribly bad.
  • Could you make like a 1Wpc SET and use it as a Preamp? I know Schiit makes those 6W headphone/pre-amps.
    deadhorse - leviathan - harbinger - shockwave (wip)
  • PWRRYD said:
      Think all pro drivers or line arrays (line arrays... hey Roman ;)  )

    Problem with many pro drivers is their 3-rd order motor generated distortions in the potential x-over region. In my experience, ideal line arrays consist of 6 to 9 drivers and with HiFI drivers it only gets you to 90-93 db sensitivity. Perhaps a horn loaded line array? That would get us close to a 100db and SET wouldn't even be working hard. I've been toying with the idea of horn line array for last year or so but my non-existent horn skills are a problem.
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