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Trace Elliot VA400, VR350, & Hexa Valve

Discussion in 'Amps and Cabs [BG]' started by tombowlus, Sep 9, 2005.


  1. tombowlus

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

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    Okay, being the gear freak that I am, and having quite the Trace Elliot tube gear fetish, I have recently picked up a VA400 and VR350, and I have a Hexa on the way (already have a Quatra Valve, Twin Valve Combo, and a V-8). Yes, I know, out of control. :meh: But, I need some help from you guys/gals in the know.

    The VA400, VR350 and Hexa Valve all employ what appears to be a similar tube output section. They all have six 6550/KT-88 tubes, and visually, there are a lot of similarities. But, not being the tube amp guru (and not being able to find a lot of information on-line), I was wondering if anyone had any information to share regarding the differences between these three. I do have the schematic for the VA400 (which I found on British Audio Service's website), but can't find one for the other two (and in truth, while I can somewhat follow the schematic, being a "layman" with regard to tube amps, it does not answer all of my questions). Any insight? Also, the VA400 and VR350 have a low, mid, and high setting for output power. Any ideas as to what exactly these controls do, and what the relative output might be at the various settings? I know that the V-8 allows you to run one or both banks of four output tubes (for 4 or 8 tubes), and I am wondering if this sets it for 2, 4, or 6 tubes?

    Any tips or references on biasing? The VR350 and VA400 have bias adjustments (I don't believe the Hexa will, as my Quatra does not).

    Finally, I have a question about the inputs on the VA400. It has a "valve preamp" input as well as active and passive inputs on the GP12 preamp section. My suspicion is that the valve preamp sends the signal to the driver tubes (like using the "instrument input" on the VR350), but yet the Gain and Master controls still have an impact on the overall volume (though the EQ doesn't seem to be in the signal chain at this point). So, my first question is what exactly is in the signal path when I plug into the "valve preamp" input. My second question is what exactly is in the signal chain when I plug into the "green" inputs on the GP12 portion of the VA400? From the schematic, it looks like I go through one half of the V1 preamp tube when I plug into the GP12 inputs, but I go through both sides of V1 when I use the valve input.

    And of course, any general comments/observations/comparisons about any or all of these amps would be appreciated.

    Thanks!

    Tom.
     
  2. Most of the useful information that I have on the Trace amps of that era came from Psycho Bass Guy. While we're waiting for him to make an appearance you may want to do an advanced search using his handle and the the amp in question. Plenty of good stuff in there.

    The only other useful tidbit that I can offer comes from one of my phone conversations with Trace's UK service manager. He told me that the service technicians hated working on the Valve Series amps (Twin, Quatra, Hexa). The subsequent models were much easier to service.
     
  3. DEVILMAN

    DEVILMAN

    Nov 24, 2001
    New York,NY
    IME, I can see why working on the Hexa style amps is a pain. Very tightly fitted internals. You have to take EVERYTHING apart to get access to the pwr sect & they have NO bias adjustability to see what's going on or to make changes...

    my $0.02
    ~S~

    PS: Tom B RULES!
     
  4. tombowlus

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

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    Lots of good stuff from Sir Psycho, for sure! :D He is an excellent resource.

    Tom.
     
  5. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    +1

    We are very fortunate to have him around.
     
  6. Total agreement here. I had previously asked PBG's permission to quote some of his wisdom by proxy, so hopefully he won't mind that I do it again here. In a short period I was able to gather a little bit on the amps you asked about. Pulling this together in one place seems a worthwhile effort so here we go:

    In reference to the VA400 (head) / VR400 (power amp):
    On tubes (related)...
    Hexa...
    I'm not intending to cause death by quotation, but this is just a small example of some of the knowledge PBG shared in past threads...
     
  7. Don't worry about it; it's wrong.

    It's a switch that lifts the cathodes of each respective pair of power tubes from ground, which leaves the tube in the circuit, but 'turns off' its emission. That's about the only simple way to reduce power level without getting into screwy impedance problems you would get if you just removed the tubes altogether. The cathode switch maintains the same primary impedance since all the tubes' plates and screen grids are still connected to the output transformer and your secondary (speaker) ratings don't change like they would have to if you just pulled pairs of output tubes: low power= one pair of output tubes putting out power; medium= two pair putting out power, and high= all six tubes putting out power.

    Yep.

    Good tubes are MANDATORY for the VA400!

    You're bypassing the GP12 preamp, which is entirely s/s, and going directly to the preamp tubes.

    The other side of the tube is for make-up gain for not using the GP12. I use my VA350 this way. The preamp doesn't sound as good as just going through the green input.
     
  8. DEVILMAN

    DEVILMAN

    Nov 24, 2001
    New York,NY
    ...hmmm, so the Hexa's pre tubes do exactly what if the pre is s/s? Does it act like an Eden Navigator & just the 2 pre tubes as a "tube front" to help color the input/sound to the s/s pre?

    ~S~

    PS: Like Dice Clay once said: "Either ya are, or ya ain't!"...
     
  9. The GP12 can be completely removed and still leave a fully functioning tube power amp. The idea is that if you want the graphic EQ and pre-shapes, then you use the GP12 preamp, but if you want tube sound with no EQ, you use the other input. The tubes are AFTER the GP12 if you go through it.
     
  10. DEVILMAN

    DEVILMAN

    Nov 24, 2001
    New York,NY
    Ok. Now, can I slave just the pwr sect of the Hexa from another pre source, totally bypassing all the Hexa's pre functions?


    thanks
    ~S~
     
  11. popinfresh

    popinfresh

    Dec 23, 2004
    Melbourne, Aus
    PBG - Are the plate voltages high on a V8 as well? Or not really.. If so, is there any better power tube for the job than others?
     
  12. I don't know about the V8. I've never even seen one in person. If anyone has a schematic, it should have voltages listed on it.
     
  13. tombowlus

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

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    Currently, it is loaded with JJ ECC83s's and (fairly new) Sovtek KT-88's, so I feel pretty good about that configuration.

    Thank you for all of your input (past and present). Very helpful stuff!

    Tom.
     
  14. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    NO WAY! Finally a tube head which PBG has never seen! It is very appropriate that the head is the V8 though...