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Ampeg V4BH Power Tube Replacement

Discussion in 'Amps and Cabs [BG]' started by V4BHDUDE, Sep 15, 2008.

  1. Hi guys, long time lurker first time poster to the best bass forum on the net.

    I have aquired my second Ampeg V4BH head recently and the previous owner was not completely honest about the age of the head or the condition of the tubes within. :meh: Having said that the amp is in superb condition for a 2002 head with what I think are six year old stock Sovtek 6L6 power tubes. Tube number designation near the base are 01 01 so I assume they are 2001 tubes?

    The amp seems to work fine but has a slight low frequency hum when the power is engaged with no instrument connected and volume and gain at 0. The hum remains constant and does not increase with more volume/gain. This caused me to check the condition of the tubes by turning out the lights to check how they glow when powered up. It seems to lack volume abit too. My other V4BH is dead silent and all tubes have a slight bluish glow when powerd up. In the one that hums only one tube has a bluish glow when powered up, the rest are slight orange like when in standby mode which makes me think the power tubes are all but shot.

    I have a new matched quad of identical stock Sovtek power tubes that were in the first V4BH I bought which were barely used but broken in and I was wondering if I could just install them to see if old power tubes are the source of the hum/volume problem without taking it to a tech immediately to have them biased? It looks like either way I will need to replace the power tubes at a minimum and perhaps the preamp/driver tubes too.

    In doing this am I asking for trouble? Would the bias voltage be so different I could potentially cause severe damage to the head/tubes or should I just take it to a pro?

    Please advise :help:

  2. Take it to a tech. I got a V4BH also & it was dead quiet at idle too. Now I got an issue with power tubes/ or biasing & there is a hum at idle.
  3. rod, any idea what caused the hum/power tube issue?

  4. Psycho >^}
    Any advice?

    I know from reading some of your previous posts on the subject an improperly biased amp will hum.


  5. That's my guess. It doesn't matter how much life is left in a tube, if it's biased wrong, it will sound bad. Also, the way tubes "glow" has little to NO bearing on how they're performing unless they're running away and the plates are glowing. I wouldn't be so quick to assume the seller mislead you about the tubes. I don't know what New Sensor (Sovtek) date codes mean, but if those are 2001 tubes, that would be in keeping with an amp made in 2002.
  6. Yeah- biasing may be it. I did try swapping pre tubes-as I had a few about- but no diff. Am taking mine to my tech Thursday. Wil let U know. As far as new tubes go, on the extensive online searching i did re 6L6GC's I found 'winged C' SED 6L6GC's to be the most popular /highly regarded by most ppl in the average price range. JJ KT66 might also be a good choice-but dunno if they'd actually physically fit in there!
  7. Thanks for your advice rod and Psycho. I have contacted a local respected amp tech to make an appointment to see him with the amp and spare power tubes today. Will post the results of his findings when I get the problem solved.

    Rod, please post your techs findings to as this may help the rest of the V4BH owners who experience this or similar hum problems.

  8. Will do. Am taking my V4BH to him Thurs am. & will let U know what happens
  9. Well I took my V4BH to My tech Yeasterday morn(Thurs) -haven't heard back yet, but he had a fair few tube amps there, so I expect it to be a li'l while!!! BUT Imagine MY surprise when I look in at the power tubes with him-spouting on about which 6L6GC will be the best for it, when I need a new set of pwr tubes --& they were SOVTEK 5881WXT tubes!!!!!!!!!!!!!!!!!!!!!!! AAAAARRGHHH What a DOPE!!

    So I see that many places list these AS 6L6GC & a few places list these as a different tube??????????

    So can I simply buy -say Winged C 6L6GC's & drop 'em in-with a re-bias of course, OR SHOULD I get the TUNG-SOL 5881 tube?? Or the same tube thats in there-Sovtek 5881 ??? THO I aren't really stoked in these- especially IF they need replacing NOW- after 1 year of use, at about 1x/week at MOST!
  10. Anyone???????????????????????????????????????????
  11. Still waiting for my Tech to get back to me so I can bring him the amp.....geez it's been almost a week now.:meh:
  12. Mine's been AT my techs for a week! Will let U know
  13. I'm still waiting for my tech to contact me but I went ahead and tried the almost new Sovtek 5881's that came out of my other V4BH. No change hum wise so I guess it's not the power tubes.

    I received a new set of TAD power tubes and a set of preamp/driver tubes today and I noticed something odd about the plate structure on one of the new power tubes. It had what appeared to be black carbon deposits on the plate where the other tubes did not. Is this normal for a tube that hasn't been in use yet or should I be contacting the store for a replacement tube?
  14. gerryjazzman

    gerryjazzman Supporting Member

    Dec 31, 2006
    New Jersey
    I'm just throwing this out. Does the V4BH have a hum balance pot (If not, I'll shut up :bag:)? The older V4's V4B's etc did (I've had a V4B and now a V4). It makes a big difference in hum level if it's adjusted incorrectly.
  15. I wish it was that easy....no hum balance pot on the V4BH.
    I'm going to have to look for an alternative tech as the one I contacted has not returned my calls in weeks.

    On the bright side, I got a nice matched quad of TAD 6L6 GC STR power tubes, a Jan Phillips 12AU7 and Tung-Sol 12AX7's for the re-tube from The Tube Store in Hamilton.
  16. The 5881 is a ruggedized version of the 6L6GB identified as 6L6WGB. It has less plate dissipation than the GC version and will give less output in given situation. Guitar players like them as they begin breaking up at a lower volume level. For bass not so good IMO unless you are the type of player that likes some distortion. Personally I would insist that the 6L6GC be fitted.


    P.S. How's the weather up north? :)
  17. Hey Paul,

    The weather is horrible....rain all weekend and a promise of snow for the trip into work on Monday :eyebrow: I hate winter....serves no useful purpose in my mind.

    I've had a set of TAD (Tube Amp Doctor) 6L6 GC's STR power tubes in my other V4BH for almost two years and they are still going strong. Good volume, very well constructed tubes and I really like the tone they put out but you have to crank them a good bit before they start to break up.

    You're quite right about the 5881's they break up too early for me and the volume is not as great.
  18. bluemushroom


    Nov 24, 2008
    I installed new tubes pre and power tubes 5881's set bias to 40mV and still have hum? on my V4BH bass head.

    I though it mite be the 47uf 450vdc filter cap? replaced it but still had the hum!

    I called and talked to Ampeg tech Scott, he thinks it mite be bad cap? coupling capacitor. Does anyone know? Where these are, I have the schematic to reference too if anyone can assist?

    Did (V4BHDUDE) get results from his tech what the hum issue he was having?

  19. gerryjazzman

    gerryjazzman Supporting Member

    Dec 31, 2006
    New Jersey
    Is the hum at 60 Hz (near the low Bflat on a 4-string) or 120 Hz (octave above that, duh)? If it's the latter (not an absolute, but...), it more than likely points to a power supply related problem (i.e. bad filter cap, either a main cap or a decoupling cap for a lower level, i.e. preamp stage). The power supply's full wave rectifier produces 120 Hz ripple that needs to be filtered by the caps. Could also be a bad/broken connection to one of those caps or a bad ground return related to the power supply. Hard to diagnose without knowing the exact layout/grounding topology of the amp.
  20. i agree with the above post. If your having a hum, its probably something wrong with the power supply, and that doesn't mean it needs a new chord, but the actually caps inside the amp could have gone bad.

    BUT its a 2002 amp...and usually those things are supposed to last a good solid 15-20 years ( on older svt's at least) IF THE AMP is used.

    if the amp has spent a lot of time sitting and not being played, the time could be quicker.

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