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Inside a Marshall VBA 400

Discussion in 'Amps and Cabs [BG]' started by EASonBass, Dec 27, 2006.


  1. Had to open up the Marshall VBA 400 to replace a pre-amp tube (ECC83) that'd gone microphonic. So while I had it open I snapped a couple of pix of the innards for your viewing enjoyment.

    Here, you can see the 2 torroidal transformers for the tubes and power supplies and a large output transformer. The power tubes are 8x6550s and the pre-amp tubes from right to left (V1-V4) are ECC83, ECC83, ECC82, ECC83. In the pic are 2 12AX7s from a Mesa, the original Marshall sourced ECC82 and a GT7025. Ended up with the 7025 in V1 (initial gain stage).
    IMG_8779.

    In the pic below is the power tube "platform". In this pic (and the one above you can see the purple and orange wiring for the output tubes. While there are 3 PCBs for pre-amp, power supplies and backpanel, the power tubes are hand wired. I couldn't lay the amp over a snap a pic at the same time. so you could see it from the bottom. The amp was "wired" by Hazel and inspected by John t.
    IMG_8783.

    Ah, the smell of glowing tubes!
    IMG_8780.
     
  2. anderbass

    anderbass

    Dec 20, 2005
    Phoenix. Az.
    Sweeeeeet.
     
  3. tplyons

    tplyons

    Apr 6, 2003
    Madison, NJ
    That's a beautiful amp. I'd love to try one out one day.
     
  4. BillyB_from_LZ

    BillyB_from_LZ

    Sep 7, 2000
    Chicago
    Thanks for the pictures! There's a whole lotta iron in that amp.

    Really makes me miss the Marshall Major I had 25 years ago...
     
  5. okabass

    okabass

    Mar 19, 2005
    Finland,Lahti
    HI

    Thank you.
     
  6. Willem

    Willem

    Dec 26, 2005
    Belgium
    Hey man
    can you give a review? Is this amp capable of loud, clean and punchy? Or only overdriven?
     
  7. pablomigraine

    pablomigraine Commercial User

    Feb 9, 2005
    New York
    VP & Managing Director - Willcox Basses
    yeah, Id love a review and comparo on this amp. A few people who've used both switched from Ampeg SVT + 810e to the VBA400 + VB810

    Whats the scoop?
     
  8. nysbob

    nysbob

    Sep 14, 2003
    Cincinnati OH
    I got to check the VBA400 out last summer. It's an impressive amp...gobs of power as you would imagine, and with that much on hand you can certainly keep it clean. If my SVT ever tanked (and I wouldn't hold my breath on that) , it would be on the short list.
     
  9. Rockbobmel

    Rockbobmel Supporting Member

    Equalisation.???
     
  10. BillyB_from_LZ

    BillyB_from_LZ

    Sep 7, 2000
    Chicago
    An absolute necessity. Helps control tonal colour!;)

    Btw, that's how it's spelled in the remainder of the English speaking world (Canada, UK, Australia, etc.)
     
  11. Gothax

    Gothax

    Apr 22, 2006
    Heerlen, Netherlands
    Endorsing Artist: Jim Dunlop strings
    sooooooo.. it has a fixed bias?
     
  12. No, it's adjustable.

    I'll get to a review for you all when I get a few cycles.
     
  13. Fixed bias is the kind you can adjust! The other kind, cathode bias, adjusts itself.
     
  14. Makes perfect sense to me PBG. Thanks, I think I've got it. So, yeah it's the adjustable fixed bias.
     
  15. Just bought a Major a few weeks ago for 750.00, definately needs some work done but I'm looking forward to using it soon
     
  16. thumbman

    thumbman Love that low end

    Nov 2, 2005
    Melbourne, Australia
    The VBA is a killer head.

    i run it through the VBC 412. There is enough clean power there to rip apart a human being...and if you want to dirty up the tone, then you can break down buildings and such...

    umm...its kinda hard to get a nice lemmy-esk ultra dirty tone at a good volume though (by good volume i mean under the thresh-hold of pain)...

    so if thats what you want...earplugs..and a hard hitting drummer

    anyone else find that or just me?

    but yeh...400 watts of all tube power...there is enough clean power...if you need more volume, then tell you guitarist to leave 3 of his stacks at home, lol
     
  17. Gothax

    Gothax

    Apr 22, 2006
    Heerlen, Netherlands
    Endorsing Artist: Jim Dunlop strings
    you could just take out 4 power tubes ;) since they're all on the same channel..
     
  18. You asked for it. Here’s my review and comparo to an SVT II (non-pro) which is one of my favorite amps.

    First, the features that you can’t see in the pics above; on the back is a fan switch (high/low), ohm selector switch (2/4) 2 speaker outs, a DI ground lift and an effects loop. The speaker outs cut the output unless a speaker cable is inserted to protect the output transformer. The effects loop is post the tone controls. I’d prefer it pre tone controls so that changes on the pre-amp didn’t go through the loop.

    The 3 position contour switch sets the overall character of the tone. Position 1 is similar to the bass cut position on an SVT, position 3 reminds me of an SVP-CL ultra-low switch in setting 5; deep dub. Position 2 is somewhere in between and my preferred setting.

    Without the bright and deep switch engaged the sound is rather bland. Bright and deep bring things to life. The tone stack is much like that in Marshall guitar amps. There is not a great amount of boost/cut available. An SVT tone stack has much more cut and boost capabilities then the Marshall. Just to level set things, I’ll use the SVT II as my reference tone. I run the II with ultra-low and bright on, bass and mid a little north of noon and treble straight up through an Ampeg 8x10. On the Marshall, with bright and deep engaged, contour in position 2, bass and treble dimed and mids at noon, the Marshall sounds much like the SVT II set as described above. The Marshall has a little less low-end boom and a little less high-end sheen then the SVT. I attribute the difference to the SVT’s greater range in its tone controls. The Marshall sounds very sweet to my ears when set up like this.

    The gain control provides for uber clean to ripping pre-amp overdrive similar to an SVT-CL. As you might gather from my liking of the SVT II’s gain control-free design, I don’t really use pre amp OD. With the Marshall I run the master up high and control the amp volume via the gain control. As with most tube amps, the tone, gain and master are a bit interactive and alter the overall tone a bit.

    Let’s talk volume. This amp is stupid loud. I know the 100 watt difference over an SVT shouldn’t translate to much more actual DB (2x electrical power = +3db) however the VBA 400 is one really loud amp. I think that’s the difference with amplitude, which is measured, and loudness, which is perceived. I can’t run the master up full as then the gain setting is barely up at all before it’s too loud. I’ll run the master at about 3 o’clock and that allows me to bring up the gain control up a bit. Then after about 10 minutes of pumping the low-end, it’s nothing but nice power-tube drive.

    Serviceability is pretty lame. To get to the tubes, the whole internal chassis must be removed from the wood case. This entails removing the back fan panel’s 6 screws and 8 bolts that hold the chassis. Then you have to carefully slide the 70lb chassis out of the case. It’d been nice if they’d made the front vent panel removable. At least then you could remove the preamp tubes without major surgery.

    Summing things up, I prefer the VBA400 with active basses as the somewhat limited tone stack can be augmented with the tone controls on an the bass. The head also sounds quite nice thorough an SVT 610HLF where a touch of horn adds a little more high-end presence.
     
  19. Great pics & Thanx for the review. I was thinkin of one o'these but bought the Bassman 300PRO instead & I LOVE IT! But if I was given an op. to buy a VBA400 at a good price....well then..... we could do BIZ.
     
  20. The 0x

    The 0x

    Aug 24, 2003
    Timonium, MD
    I REALLY want to try one of these amps out.
     

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