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Peavey VB-3 Service Manual/Biasing

Discussion in 'Amps and Cabs [BG]' started by TheCreature, Aug 22, 2012.


  1. TheCreature

    TheCreature

    May 22, 2002
    Dallas, TX
    I just received a used Peavey VB-3 and it has a mismatched power tube pair in there. There's a little hum when operating. Inside there's one knob labeled bias adjust, a switch for EL34 or 6L6 operation, and two test points for making bias measurements. I'm wondering, as long as the tube pairs are matched, is there any reason to do a bias adjustment other than changing to 6L6s?

    Does anybody know how to get my hands on a service manual?

    thx

    DaveJ
     
  2. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Contact Peavey they're very good with supplying needed information for their products.
     
  3. BbbyBld

    BbbyBld

    Oct 13, 2005
    Meridian, MS
    That depends. Since you bought it used, you never know if someone screwed around with it.

    What kind of tubes are in it?

    Just out of curiosity, is yours tolex covered or does it have the bedliner coating?

    You should be able to call in and get a full schematic set, but there is no service manual for it. I wrote a biasing procedure for the service centers, but I don't know if they give it out. I guess it doesn't hurt to ask.
     
  4. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    SEE!!! I told ya so!! :D

    Great job Bobby! :)
     
  5. TheCreature

    TheCreature

    May 22, 2002
    Dallas, TX
    It came with all JJs (7 of them), except for the one tube behind V6 which is a GT. All the JJs have a rating label reading 25. I'm guessing they're original. Can I use another JJ marked 25? I have a new matched pair of GTs - can I sub them in for the mismatched pair?

    I REALLY appreciate talking to the factory Bobby - thanks.
     
  6. TheCreature

    TheCreature

    May 22, 2002
    Dallas, TX
    It's Tolex BTW. It was on Ebay with the disclaimer "It works fine except you have to turn it on, then off, then on again before it turns on fully". I know SMPSs can be a little finicky so I bid $520 and won the auction. I have not experienced the power cycling issue the seller mentioned. Haven't had it to a gig yet...
     
  7. BbbyBld

    BbbyBld

    Oct 13, 2005
    Meridian, MS
    You got a killer deal my man!:bassist:

    I don't like GT tubes for anything. In my experience, they are just overpriced, regular tubes. I've never tried them in this amp.

    I would just order a 25 JJ either from Peavey or from where ever you can get one. Chances are the bias is still set from the factory and it will be fine.

    The VB-3 power supply is universal, meaning you can use it anywhere in the world without having to change anything. On the very first ones, sometimes the amp thinks you are running in a 230V country if your 120V outlet is running a little high. It will still power on, but the output will be low and distorted. The solution is to flip it off and then right back on again. That's what the seller is talking about. That problem was fixed 3 years ago. If it becomes an issue, the power supply is modular and can be replaced by either the factory or a dealer service center.

    I'm betting that this amp originally came from an artist, and is a beta unit. As far as I know, none of these shipped to customers with the power supply issue and with JJ tubes. The regular production units use Ruby BHT's.
     
    Mills567 likes this.
  8. TheCreature

    TheCreature

    May 22, 2002
    Dallas, TX
    Bobby - thanks so much for your insight. I did get a killer deal! The amp's pretty much spotless, no dust on the fan blades, etc. I'll look around for that tube. Got to be one here in Dallas somewhere.

    Thanks again

    DaveJ
     
  9. kilgoretrout1

    kilgoretrout1

    Aug 13, 2018
    Hey all, I realize that this thread is 6 years old, but there's not a lot of info out there on this beast. Also, after a conversation with the tech assistance dude at PV, there seems to be errors on the schem. This thread kept coming up in my searches, and I noticed that a dude that must've had a part in engineering this amp was on here. Hoping for a hand as I'm confused. I have one that was horribly abused. When I got it, it was blowing caps, and DOA. Turns out, the tech that I bought it from and had worked on it previously, plugged the cable assembly carrying the power rails that goes from the power amp pcb to the preamp pcb in backwards, sending B+ and B++ down the +-19vdc rails, and reversing polarity on the +-30vdc rails. I replaced all of the blown caps on all PCBs, Replaced all ICs on those rails, the smps seems to be putting out all of the right voltages. I have confirmed that the preamp PCB is now functioning, by plugging the preamp out into my OR-15 return. Now, everything seems to work, except the output is super low and distorted. According to my bias probe, I have 510 vdc on the plates of the power tubes, but the max bias current no matter where I set it with the trimmer on the PCB, won't go above 20mA. This explains why the output is low and distorted, and needs to exceed a certain amplitude to even be heard. I assume the bias circuit on the vb-3 is similar to that of the 6505+, 3120, xxx, etc, and the points only show the -VDC on the bias circuit, but the current on the cathodes is cold as f**k, no matter where the trimmer is set. Can I get that bias procedure you spoke of? or a bit of troubleshooting assistance??
     
  10. Passinwind

    Passinwind I am Passinwind and some of you are not. Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Since you didn't quote anyone, I assume you're talking to Bobby Baldwin, who used to be Bass Amps Engineer at Peavey? He hasn't even logged into TB for around six months. You could try PM'ing him (AKA "conversation"), but I'll also throw out a page to him like so, just in case: @BbbyBld
    Best of luck, and welcome to TB. I've never even seen one of those amps in the wild, so I'm afraid I can't help at all in this case.
     
  11. kilgoretrout1

    kilgoretrout1

    Aug 13, 2018
    Thanks man, I was indeed referring to him. Sorry, I'm a noob to forums. Also, I just found that if I poke the smps PCB with something (a chopstick), the plate voltage on my probe drops dramatically (as low as 180vdc). This is surely the root of the issue, and probably the issue the previous tech was trying to fix when he blew the darn thing to hell. Just hoping to salvage this thing ya know? I'll PM Bobby, and see if he has anything to say on the subject. Thanks.
     
    Passinwind likes this.
  12. Passinwind

    Passinwind I am Passinwind and some of you are not. Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Bobby's a very cool guy and is greatly missed as a regular here. If you can't reach him within a a few days please PM me and I will try to expedite.
     
    jwindham and BassmanPaul like this.
  13. kilgoretrout1

    kilgoretrout1

    Aug 13, 2018
    Thanks man. Good lookin out. I pm'd him. I'll let yall know how it turns out, and keep pokin at it in the meantime.
     
  14. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Please don’t. Have you not heard the axiom about poking the beast? Leave it be until you get it to someone knowledgable about the amp who can fix it for you.
     
    agedhorse likes this.
  15. kilgoretrout1

    kilgoretrout1

    Aug 13, 2018
    It's cool man. I have a lot of amp work under my belt, and I'm fully aware of how to safely work on a tube amp. This one with the smtp though is unfamiliar. Not many switch mode power supplies in tube amps. The poking I was speaking of is the old tried and true chopstick method wherein you poke and jab with a chopstick until you get a wobble on your scope and or meter to identify the problem area. Doing just that, I found that the component that seems to be giving me issues is T1, a current sense transformer. I can tap the components around it, but just the slightest tap on the toroid itself, and the plate voltage drops dramatically. I also noticed that when that happens, the slight switching noise stutters and quits. I assume that this is a function of the smpt, but it seems too sensetive.
     
  16. seamonkey

    seamonkey

    Aug 6, 2004
    Ferrite core? Sometimes the cores break when subject to mechanical shock
     
  17. kilgoretrout1

    kilgoretrout1

    Aug 13, 2018
    Not sure. I gotta call peavey and check the part specs. It seems to be the sensor for the overcurrent shutdown mechanism so it makes sense that it is killing the current when it freaks out. It's a starting point anyways. Damn technology. Troubleshooting a traditional supply circuit is a piece of cake in comparison.
     
  18. kilgoretrout1

    kilgoretrout1

    Aug 13, 2018
    Hey dudes. I set this one aside for a while, until I could afford a matched octet for it to rule out tubes. It's all up and running now. (Kinda) I resurrected the preamp section, and the power section, and I'm running a fresh octet. Now I'm getting the same issues that the OP of this thread had. HAHA! Dammit!
    It hums, and the output is low and distorted. On the High voltage DC output from the SMPT (Red Wire), I'm getting a fat distorted sine wave where I should be getting High voltage DC. (See scope shot) It is the proper voltage ~510V DC with about 1.5 volts of 60hz ripple. Anybody have any insight?
     

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