Custom V4B build from scratch...

Discussion in 'Amps and Cabs [BG]' started by kiljoy, Jun 29, 2008.

  1. Hi guys, I'm about to embark on something of a mammoth task which is to build an early 70's style V4B from scratch with some power section modifications. I wanna keep the preamp as is but switch out the 7027s for KT88s and feed them the right power via a bigger power tranny to get the output to 200w. I have a good tech who will be doing the actual build as I'm fairly ******** with a soldering iron.

    Are there any hints, tips or advice anyone can share?

  2. Stand back and watch?
  3. That's what I'm gonna do. :cool:<---solder-proof goggles
  4. anderbass


    Dec 20, 2005
    Phoenix. Az.
    Sounds like a very cool prodject, but it might be easyer (and much-much cheaper) to just have him modify a real V4/V4B.
    I've seen-em going prety cheap ($200-ish) in need of a replacement tranny...
  5. Bassmec


    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    I agree its much better to get an old blown up one and mod that. I do that all the time you get a decent pair of transformers and a good choke
    some better faster diodes a few muticaps and replace all the lytics
    and you are there. I always copy the Hiwatt Dr 201 output Schematic
    and I always use matched Gec KT88 tubes in fact the tubes always come before I buy a suitable amp. There is no point in going off half cocked.
  6. kringle77

    kringle77 Supporting Member

    Jul 30, 2004
    Massena NY
    1) Thats a great idea! A really great amp that could use a hundred more watts!

    2) Why not just get an old SVT? They will weigh about the same and the preamp sections are nearly identical. It would probably be cheaper too.
  7. Thanks for the replies fellas. I'm in New Zealand which happens to be the arse end of the world so even if I did find a V4B on ebay or the like it'd cost about twice as much in shipping to get here and that's if the vendor could even be bothered to ship here because most don't.

    I prefer the sound of the V4B's preamp to that of most SVTs, It's a bit dirtier and less subtle. I just need extra volume, headroom and bandwidth which is what I'm hoping to get out of the KT88s.

    Is there a transformer upgrade anyone can recommend? My tech has an old guy that custom winds them but I think he may be quite pricey. Also recommendations on chokes, caps and any other related stuff would really help me out.

  8. Sounds like a killer project. Good luck and keep us posted.
  9. metron

    metron Supporting Member

    Sep 12, 2003
    Not to be discouraging but that is going to cost a small fortune in labor and parts. Probably more than the price of an SVT shipped all the way around the world? One way or the other, good luck!
  10. gillento


    Oct 15, 2005
    Luxembourg, Europe
    Nordstrand pickups
    What about a Hiwatt clone:

    100watts, 200 watss or 400 watts....

    I'll be getting one of these later today :)
  11. BassmanPaul

    BassmanPaul Inactive

    You will need a power transformer capable of delivering 600V for the plates and 400V or so for the screens. Negative 60V bias and 6.3V AC at about 10A for heaters. Output transformer rated at 200W with a primary impedance suitable for paralleled KT88. IIRC about 18/1900&#937; plate to plate. These will be big, heavy and expensive. Be prepared that you will end up paying more for this beast that you would pay for a commercial offering. The other side of the coin is that you will know the quality of the components that you used.

  12. Would a Marshall Major power tranny do the trick? Or maybe a Hwatt Custom 200?
  13. Looks like we're going with a custom wound power transformer and a Mercury Magnetics Hiwatt 200 output tranformer.
  14. chicago_mike


    Oct 9, 2007
    Chicago - LA - Rome - Dallas
    Endorsing Artist : Genz Benz
    Dynaco used to make the trannies for the Sunn 2000s. I dont know if those are still around but they are very nice and dont have to be run ultralinear so you get 240 watts rms off of 4 kt88's. I was always thinking of building my own Sunn 2000s with an swr style preamp.
  15. Ok, after much deliberation with my tech guy we've decided to can the build from scratch idea. It seemed to be a cost effective idea in the outset but ended up calculating far too high in price. So... I've just bought myself an Ampeg V4BH which I know is nothing like the original V4B but it was all I could find in this half of the world.

    I'm still considering the upgrade to KT88s and potentially a transformer upgrade too. Does anyone know of any preexisting modification to do this?
  16. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    Why are you considering a tube change and a transformer change when you haven't even heard the amp yet? Who knows? It might be perfect as it is.
  17. I've played through a friend's V4BH once before and although I liked it I found it too 'guitar' sounding. I find 6L6's are very focused in the mids and don't sound good bs power tubes in bass amps (the Mesa 400+ is a perfect example). We've now decided on 6550 instead of KT88's as the tubes are mounted upside down in the chassis and will be more reliable.
  18. playibanez


    Apr 3, 2006
    I don't know much but just want to butt in for one thing.

    You said you like the V4 because it isn't as subtle. But isn't this because its a 100 watt tube amp and breaks up faster. And adding another 100 watts might change this character of the amp.

    Again, just a thought.
  19. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    I don't know if I buy that. My B-15's have 6L6's, and if you record a direct out from the OT with a Red Box, it sounds pretty flat IMHO. Plus if they were that heavy on the mids, guitarists wouldn't use them as prevalently as they do.
  20. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    My 70's V4 has been modded for 6550's. The tech that did it is a good friend and he said it's a fairly easy mod, one that he's done a lot over the years before 7027 became readily available again. I'm not sure how easy it would be for the V4BH, but that might be an issue you could PM someone like Jerrold Tiers on to get some better insight.

    -> From what I understood when he explained what he was going to do to my head, in the 70s amps its mostly just an issue of changing out a few resistors and such. But there may have been a few details that slip my mind right now. And again, I dont know how that would pan out for a V4BH