high wattage class A amps?

Discussion in 'Amps and Cabs' started by dave s, Aug 21, 2005.

  1. dave s

    dave s Member

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    Comment while playing out last night. A guy asks me if my matchless amp was 100 watts. I told him it was only 35w and he was amazed for some reason.

    Which got me to thinking ... most of the class A amps I know about are matchless, VOX and a few others. Most of which are in the 20-40 watt range and utilize EL84 power.

    Are there any real high-wattage (not that I NEED one!) class A amps out there? More than 50w? 100w?

    thanks in advance for the info.

    dave
     
  2. Scumback Speakers

    Scumback Speakers Gold Supporting Member

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    I'm in the design/features stage of a single ended Class A amp right now. Leaning towards a dual 6550 or dual EL34 amp. It will be awhile before it's ready, though. Likely next year.
     
  3. TaronKeim

    TaronKeim Member

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    Bad Cat makes a 100W version of their Hot Cat using EL34 tubes and it is still cathode-biased Class AB. And I think Matchless used to make a 100W amp as well (might be 50W, can't remember) called the Super Chief.

    -TJK
     
  4. heybulldog

    heybulldog Member

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    the super cheif was 100 watts but it was not cathode biased. mcintosh made or still makes 75 watt amps i belive they are class a

    hey dave- im gonna have my clubman and es410 at the lime spider on saturday night. for more info check out:

    hometown.aol.com/jamgtr
    james
     
  5. theelectic

    theelectic Guest

    Can anyone else confirm this? There's a chassis pic of a Super Chief here:

    http://www.acplink.com/chassis/display.aspx?curpage=94

    Check out the huge, heatsinked power resistors on the left. What else could they possibly be used for except as cathode resistors?
     
  6. Gary Brennan

    Gary Brennan Old cavorting member Gold Supporting Member

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    The original Groove Tubes Soul-o 75 and 150 amps were supposed to be about 70% of those power ratings when run in class A, so this would be around 50 and 100 watts. I don't know enough about it to know if they are ligitimate class A.

    gb
     
  7. heybulldog

    heybulldog Member

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    phill jamison stated that those amps needed to have the bias set-and where not self biasing- i have never seen one (chassis) i did see sara lee play one with the b52s(for bass!)
     
  8. theelectic

    theelectic Guest

    True Class A can only be at most, 50% of the max plate dissipation of a tube, and in reality, will usually be less. So a single 6L6GC that can dissipate 25W max, will at most dissipate 12.5W in Class A, and more likely, 10 or 11W.
     
  9. Onswah

    Onswah Member

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    I read somewhere that in order to have a true class A at 100watts you'd need something redonkulous like 10 power tubes to make it happen...
     
  10. glynn

    glynn Member

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  11. JacksonAmpworks

    JacksonAmpworks Member

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    That's pretty accurate. I know that Allesandro has a 4x EL34 amp that puts out 25W of Class A power. So yeah, make it with 16 EL34's and there you are! :)

    Funny thing, you add 12 EL34's and you only get 6dB louder, doesn't make sense does it? Also considering the real estate and the GINORMOUS Power Transformer that you would have to use to power the heaters from 16 EL34's. (25.6 AMPS!!!)

    I would not really be practical, but it might sound REALLY cool.
     
  12. r9player

    r9player Silver Supporting Member

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    But Wattage is not just about louder .. it is also about headroom no?
    Also and I am not sure why but oft people will feel that a 40W version will sound better then the 20W version etc.
    I sure notice the increase in headroom on my Holland Brentwood now a 100W head with Monstrous headroom vs. before my 35W Brenwood which had a lot of headroom but could be overdriven with single coils.
     
  13. John Phillips

    John Phillips Member

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    I don't know, but that looks like a fixed-bias amp to me. Look at the two small filter caps nearest those resistors - they appear to have their positive ends grounded and their negative ends linked by a resistor - that's a bias supply network. The blue component half-hidden by the wiring loom (with the 33K resistor going to it, from the ground end of the caps) looks like a chassis-mounted trimmer.
     
  14. Kiwi

    Kiwi Silver Supporting Member

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    Dumb question:

    If the Clubman is cathode-biased, does that mean it's self-biasing? So if I swap power tubes, I don't need to rebias?

    Kiwi
     
  15. VacuumVoodoo

    VacuumVoodoo Member

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    That's correct for EL34 in triode mode. You'll get more power in pentode mode but then you may lose some of the sonic advantages of triode mode. Such a scheme would be, as so correctly pointed out, pretty ridiculous.

    I've had pretty nice results with the EL156, ca 25W in SE class A1 in pentode mode, can be scared to well over 50W in PP clas A1 with cathode bias. This was a Telefunken original and is now back in production by Shuguang and, can't rememebr who else...

    A very interesting tube.
     
  16. Shea

    Shea Member

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    Some '68 Twin Reverbs are cathode biased, sort of .

    Shea
     
  17. Roe

    Roe Member

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    the biggest matchless is the 200w thunderchief (4xkt100/88).
    it's a bass amp. less than 100 amps were made. (my band has been using one for a year or so.)
     
  18. Tony Foran

    Tony Foran Member

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    I have a cathode biased Silvertone with 4-6l6s. It was rated at 150 watts,but I imagine it's closer to around 60.
     
  19. theelectic

    theelectic Guest

    I was googling around and found a link where it was said the Superchief runs 540V on the plates and 54ma idle. If the cathode resistor was in the typical EL34 range (say, 300 ohms) that would put 16V on the cathode, 540-16V = 524V*54ma = 28W idle per tube... yikes!

    Then again, looking at that pic:

    http://www.acplink.com/images/6superchief.JPG

    It looks like the grid resistors (pin 5) are 10k, and the big 10W sandbox resistors are on the screens (pin 4). The four power tubes appear to have different coloured wires on the cathodes (pin 8) two have red, two have black, which run under a hidden wiring loom. If the cathodes are supposed to be grounded, why not just ground them close to the sockets (OK OK noise/hum/etc. considerations)?

    But then, what the heck else could those huge power resistors be for? Filter cap bypass? Then what are those 220ks straddling the filter caps for? They look to be at least 2 inches long, which would put them in the 50W range. Check out these Ohmite ones:

    http://www.ohmite.com/cgi-bin/showpage.cgi?product=hs_hsn_series

    I doubt it could be any other Matchless amp - what else would have four power tubes and two rectifier tubes? Maybe it's an early/custom Superchief that's cathode biased?
     
  20. monstermike

    monstermike Member

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    Either way, I bet that big Matchless makes an excellent space heater in the winter...
     

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