Ampeg V4B ?

Discussion in 'Amps and Cabs [BG]' started by MJS, Jan 22, 2005.

  1. MJS


    Dec 30, 2001
    Malibu Ca.
    I just purchased a V4B, 76-79 that appears to be in xlnt condtion. It has all original tubes (magnavox) and sounds fine. I was going to buy a new model of this amp and saw this one For $ 500.00. Is this price about right and what are the main differences. It has 7027 power tubes and if they need to be replaced can you safely change these out to 6550's. I play thru a ampeg B4r now, this more for the fun of having a vintage amp playing small to medium rooms or mikeing for bigger venues. All info welcome, thanks, Mike
  2. MJS,

    Congrats on you find!
    I haven't really been keeping up with those as far as price goes.
    But hey, If the caps are in good shape and you don't need to send it out for any repairs, you're O.K.
    It's a great amp and at 100 watts should have more than enough headroom for your average rock band.
    What are you running for cabs?
    They call the V4b the, "Baby SVT".
    I had one for a couple of years and decided to sell based on the weight.
    IMO, There was always a clarity of tone from those vintage Ampeg's
    As I remember it had more grind than an SVT so it should shine for rock and roll.
    While I'm not an expert on tubes I recall the 7027's being very close to 6L6's.
    I do beleive you can set the amp up with 6550's but never went that route.
    It did the job for me with the 7027's.
    Post a picture of your setup.:bassist:
  3. Decent price if the amp is in good condition.

    7027's are readily available brand new (Sovtek makes them), a quartet from Parts Express was $80 or $90.

    6550's require a minor mod, there's a very minor power increase, IMHO it ain't worth the trouble but some people think it's worth doing...

    If it sounds fine, keep going with the original Magnavox tubes.
  4. TyKao


    Jun 29, 2003
    I've heard of people doing this tube conversion from 7027s to 6550s. I think the bassist for Rainer-Maria did it. How much power does one gain from that?
  5. The 0x

    The 0x

    Aug 24, 2003
    Timonium, MD
    I think it only boosts them to 120-140 watts.
  6. I've seen claims it'll bring it up to 130 watts. However, somebody--Psycho Bass Guy I believe--said he only measured 110 watts after the conversion. Since the amp already makes an honest 100, a 10 watt increase isn't enough to worry over, IMHO.
  7. Passinwind

    Passinwind I Know Nothing Supporting Member

    I have one on my bench right, which I'm renewing for a fellow TB'er. It has 6550s, and is outputting around 105 watts at clipping right now. That may go up a bit when I put in new filter caps and tweak the bias. The AC in my house is generally a bit higher than normal, so I often measure a bit more power in amps on my bench than what they'll do in a typical club.
  8. After I completely recapped my early 70's V4, I measured exactly 100 watts when clipping was evident on the sine wave on my scope.

    This was with a completely mismatched set of old ancient well used tubes. So I replaced with the brand new matched set of Sovtek 7027's. I measured....exactly 100 watts, same as before.

    So if going to 6550's only gains me 5 or so watts, I figured, why go to the trouble (and risk damage to the power transformer from the extra filament current draw)???
  9. Nashvillebill,
    That's very interesting!
    Mismatched tubes made no difference in power output.
    What is all the hype about matched power tubes anyway?
    Can you explain?
    Did Ampeg match tubes back then ?
  10. Passinwind

    Passinwind I Know Nothing Supporting Member

    Matched tubes will produce less noise at idle in the typical guitar amp configurations, and may wear more evenly. IOW, the full power output of the amp doesn't tell the whole story. If you were to use a distortion analyzer, you would likely see worse results with the mismatched set. Your ears might moot this, however.

    Back in the day, many tubes seemed pretty well matched right off the production line, in my experience. But Fender used a balancing control in lieu of a standard bias adjuster for quite a few amps, which implies that they didn't think this was always the case. It's possible to have a circuit that combines both approaches, but well-matched tubes are readily available these days, so why bother?

    Edit: here's one manufacturer's take on the subject:
  11. MJS


    Dec 30, 2001
    Malibu Ca.
    Thanks everyone for the info, I will know after I have a tech look at it whether or not It was a good deal. Good to know the price was ok. Looking forward to playing thru it.

    Thanks again, Mike
  12. Rockbobmel

    Rockbobmel Supporting Member

    I bought my 72" used about 6 years ago. It has a set of GE 7027A tubes that were put in in 1986. I have NO intention of changing them. If I did, it would be 6L6GC tubes. Since the 6550s do not yield much more.
  13. For a completely irreverant view of tube matching and biasing, read through this site:

    Makes you think.
  14. Passinwind

    Passinwind I Know Nothing Supporting Member

    I think he likes the sound of distortion, mainly. :cool:
    But, at least he's upfront about that. I've enjoyed that site for years.
  15. well that was an intresting 2 hour reading.
  16. Apparently the 7027's were out of production for a long while, and that's what initially drove everyone to switch to 6550's.