Trouble removing Ampeg V4B from the case??

Discussion in 'Amps and Cabs [BG]' started by groovaholic, Nov 8, 2012.

  1. groovaholic

    groovaholic The louder the better. Supporting Member

    Sep 19, 2004
    Grand Rapids, MI
    I stumbled upon (and subsequently bought) an Ampeg V4B today; the version with two inputs, a 6K11, and the metal switches on front.

    One of the 7027s was cracked, but the amp still functions, albeit obviously not up to it's full potential.

    Cosmetically, the amp is dusty and cobwebby, but probably a 7/10.

    So, I wanted to install a grounded power cord, check the condition of the caps (the tubes were all original Magnavoxes, so I strongly doubt that a tech has EVER been inside this amp).

    BUT -- I'm stalled at the starting gate! I can't get the PT side of the chassis out of the case...something is stuck and I don't want to apply excessive force.

    It seems like it just needs to lift up a bit to clear the front grille, but I can't get that side of the amp to budge.

    Is there a trick, some common problem that I'm running into, or do I just need to eat my Wheaties and muscle up on this thing?
  2. groovaholic

    groovaholic The louder the better. Supporting Member

    Sep 19, 2004
    Grand Rapids, MI
    Alright...I got the amp apart and, as I suspected, it's a total time-capsule in there.

    I know the amp might have better resale if it's stock, but my instinct is to do some updates (caps, grounded cord, bias pot, upgraded screen resistors, etc) to make it a PLAYER.

    Part of that urge comes from the fact that one of the knobs is missing & replacements go for $30...***? I'm tempted to sell the remaining 4 to finance a retube, put some chicken heads on there and call it "custom"...

    It also needs a new power light -- so I'm thinking LED to prevent ever having to replace it again...

    Anyone have any thoughts or opinions on it?
  3. Foz


    Jul 26, 2008
    Jax FL USA
    Players got to play. I say set it up to run or sell it to a guy who wants a museum piece [unless that's you of course].
  4. No need to replace the screen resistors, also don't put chicken head knobs on they always look cheap :( Bulbs are real cheap to!

    my recomendation is replace ALL the electrolytics, then go through the amp and check every resistor, any thats over 10% out from the rating - replace it. Do the same with the caps. Also spray and clean all bases / pots and jacks.
  5. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Congrats on the new amp. Since it isn't a museum piece, performing needed maintenance is not going to lower the value. It will enhance it.

    I think that those metal knobs add to the look of the amp. I would be patient and try to find a replacement on ebay. You might find the lamp at They also have knobs but that one is rarely in stock. There is a section with NOS parts and they have Ampeg lamps.
  6. The pilot lights are actually neons with a resistor built into the case, and that resistor usually drifts way up so the light doesn't work anymore. You can either find an exact replacement neon assembly for it (I think it goes in a 1/4" hole), or if you have the skills, you can cut apart the old one, replace the little resistor with a new one of the same value (usually like 220K), and it will probably work again. My standby light has never worked, and my AC light flickers once every minute or so, so I've never changed them.

  7. groovaholic

    groovaholic The louder the better. Supporting Member

    Sep 19, 2004
    Grand Rapids, MI
    Bingo! The little resistor inside the heat shrink tubing was burned out. Mine was orange-black-orange, so 30K...that'll be an easy enough fix and I even have some of those resistors in my toolbox.

    While soldering in a 3-prong power cord, the soldered-in 10A fuse fell apart, so I'm going to wire in a fuse holder to simplify future replacements; I've heard that the flyback diodes tend to go south eventually and take out the fuses when they do -- and I don't want to be soldering a fuse in place every time.
  8. Bassmec


    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    Only very tone sensitive bass players will appreciate a V4B, so if you are, you obviously ain't heard or played through a V4B in your life.
    Or you would know why us old gits love them to bits.:bassist:
  9. groovaholic

    groovaholic The louder the better. Supporting Member

    Sep 19, 2004
    Grand Rapids, MI
    Got the ol' girl cleaned, retubed, and reassembled.

    I measured the plate voltage prior to biasing and it was at EXACTLY 540 VDC, just like the schematic said it should be!
    For it to be that close, it seems like most of the components must be holding their values.

    The amp only has 2 remaining issues:
    - I replaced the 30k resistor on the power light and where it was totally dark before, now it flickers. I'm OK with that; at least I have an indication of mains power when the amp is on standby. If it starts bugging me, I'll spend the $8 to get a replacement from Fliptops...

    - Channel 2 hums when nothing is plugged into it. I'm 99% certain this is a simple fix of getting the jack to short out when the cable is removed, but right now it's easier just to plug into Channel 2 or keep its volume all the way down when plugged into Channel 1.

    It's a pretty cool amp, that's for sure!
  10. Rockbobmel

    Rockbobmel Supporting Member

    Best sounding bass amp on the planet. Period! :bag: