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maybe buying a broken ampeg v4....whaddya think?

Discussion in 'Amps and Cabs [BG]' started by rokkitt, Oct 28, 2009.

  1. rokkitt


    Jun 7, 2007
    bronx, nyc
    so, I know I shouldnt do this,

    but I need a project to pull my hair out!


    here is the story-----

    Ampeg v4

    Powers up.

    Low volume bad volume scratchy and inconsistant volume

    Thoughts on how to fix?

    I have electronics skills. A volmeter and a few soldering irons...those things that get really really hot when you plug them in.....dont scratch your ear with them! -actually know someone who did this...ouch!--

    And I can read a schematic


    Is it worth say 300 to 350 dollars? they are asking $650

    Any one have a schematic they could email me?

    At least it powers up so it seems the power supply is good.


    (I know this is gonna turn out bad.....but could I get some serious answers on this? any of you guys repair these things?)


  2. rokkitt


    Jun 7, 2007
    bronx, nyc
    hi, just an fyi...

    I have heard that it isnt the tubes, that it was more than that....that is what the salesguy says.....but I dont know his technical ability though

  3. grifff


    Jan 5, 2009
    Towson, Maryland
    How does he know it's not the tubes? If he knows that it isn't the tubes then I would assume that he knows what's wrong with it/if it would be costly to repair. IMO.
  4. That is the price of a non broken V4.

    IMHO, even if it's an easy fix (bad volume pot), don't pay more than $100 or $150 for it.

    Could be a $7 pot, could be a $250 transformer (maybe not in this specific case, but I'm just saying in general)
  5. Thor

    Thor Gold Supporting Member In Memoriam

  6. I agree that that is way too much money for a non functional amplifier. What could be wrong is how techs make their money. As has been posted it could be anything. If you have had experience with tube amps the repair should be fairly easy. If not, heed the warnings about lethal voltages.

    If you feel you should continue, think how much you are prepared to put into this. At worst you will waste that much money. At best you'll have a learning experience and a working amp.

  7. rokkitt


    Jun 7, 2007
    bronx, nyc
    yah, the 650 seems if it is a full working unit

    they are willing to negotiate.....

    lemme check the schematic, and rethink this....

    hey at worse, if I trade it for an amp I am not using, --harkte 7000-- and it is a pile of parts, maybe I can get a few dollars out of it...

    but like I said, I do have some electronic skill, and maybe it is the tubes....who knows?

    any tips to diagnose it further? prolly just taking a shot in the dark at this point.

    thanks for the info so far....
  8. sounds like a bad output transformer + a few other problems. don't do it unless you get it real cheap
  9. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    Could be anything
    You don't want it to be OP transformer as that's the money item
    If it's at a good shop with a tech, and the fix was easy, it would be working and for sale at $650
  10. j_rod


    Oct 6, 2006
    Got my VT22 for $250, power light comes on but no sound at all. A couple resistors later and we are back in business.
  11. Yeah- they cost money. Tell him if its so easy to fix to get it fixed. My bet is atleast 150 for a tech to get it running if it is something simple. Which is about how much I would pay for a broken amp like that!

    Do you have any lab equipment to trace signals, generate tones, test voltages (is your meter rated for them)?
  12. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses

    a bad output tranny is my first guess too!
  13. $650 is how much a working V4 costs. For a non-functional one, that's a ripoff.

    I'd pay a couple hundred for it, tops.
  14. gerryjazzman

    gerryjazzman Supporting Member

    Dec 31, 2006
    New Jersey
    Assuming that you do get this for a price that you're comfortable with (for $650, even $500, look for another one that's working), the first thing I would do is after a visual check of the guts for any obvious signs of overheating, burn't resistors, etc (the preamp tubes have a cover on the top of the chassis that needs to be removed to expose the component side of the circuit boards), power it up and with the schematic in hand check all the voltages to make sure they're within probably 10% to 15% of their marked value. After that you can try narrowing it down to the preamp or power amp by using the external amp output to another power amp (make sure you always have a speaker connected to this though so you don't flashover the output transformer or output tubes). You can also try using another amp as a preamp and driving the V4 output section via the same external amp jack (works as an in or out). You can also carefully look for any bad solder connections. I found a number of bad (corroded?) connections of wires coming from the tone control pots on the front panel to the preamp board of my V4 which caused some intermittent problems with the tone controls (e.g. sometimes the mid control would have no effect). I had to reflow those connections.

    I also had a similar problem with my V4 with the volume wavering and practically cutting out and it turned out to be a flakey screen dropping (power) resistor for the output tubes in the power supply. I found this by monitoring the screen voltage while I played through it on the bench and saw it gradually decrease from about 500 volts all the way down to like 100 volts or so. Take Paul's advice and be REALLY careful when you do this kind of stuff (one hand in your pocket or behind your back if you go poking around inside). There is 550 volts inside of that thing.
  15. rokkitt


    Jun 7, 2007
    bronx, nyc
    good info---will probably end up getting this, and giving it a try...

    will keep you posted... and , thanks for the info on the voltage.

    yes, I would be careful poking around there....but thanks for reminding me!

    I have some pics somewhere, lemmme check
  16. rokkitt


    Jun 7, 2007
    bronx, nyc

    gotta change that knob! may be not, adds mojo! :hyper:
  17. rokkitt


    Jun 7, 2007
    bronx, nyc


    these are cell phone photos..... so a little blurry
  18. rokkitt


    Jun 7, 2007
    bronx, nyc
  19. Papazita


    Jun 27, 2008
    How about a V4 with cab, circa 1973 (maybe) for $750. Amp doesn't turn on at all... :eyebrow:
  20. Somebody added a master volume to it?????? Had to be a gui****! BTW the schematic should be on the top cover of the head when you remove it from the case.

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