Re-tubing PV VB-2

Discussion in 'Amps [BG]' started by RockBobby, Nov 15, 2012.


  1. RockBobby

    RockBobby Supporting Member

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    Been reading some and heard the 6ca7 tubes had bigger better bottom than el34 or e34l tubes. I have a set
    Of JJ el34 in there and have to max
    Out the bass control to even get a modest oomph!
    It seems el34 tubes were
    meant for guitar amps.
    Any advise? I will prolly go on the cheap with EH or JJs.
    Any experience with these?
    Thanks. Bob
     
  2. BbbyBld

    BbbyBld

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    EL34's don't have any less low end than other power tube types. They generate a lot of harmonics in the mid range, which gives them a really full, but forward sound. If you change to 6CA7's, you have less harmonics, so the low end stands out a little more, kind of like if you turn the mids and high controls down, it can sound like you turned the bass control up. This also means that the 6CA7 sounds smoother. When you overdrive the power section, you'd get more grind and less grit.

    The VB-2 was designed with the deep low end rolled off so you get the maximum clean volume before clipping. What you're left with is the low end that cuts well in a mix. The resonance control can add a lot of the deep low end back if you crank it up. Also, instead of turning the bass up, try turning the highs and mids down a little. Also, Also, if you use the 200Hz mid shift setting, you're low control EQ center will move down lower to a frequency that may give you more deep low end.

    The Electro Harmonix 6CA7 is a fine choice for the VB-2 and may help get a tone you like better if you decide to go that route.
     
  3. iiipopes

    iiipopes Supporting Member

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    +1 on the ElectroHarmonix "big-bottle" 6CA7. Not as complex as an EL-34, but really big and clean, "bigger" than the standard 6L6GC. Same plates as a 6550, but not as "edgy" to my ears as a 6550.

    Actually, in their "linear" mode, the EL34 was designed for "hi-fi" applications. It's only when pushed do they give the tone associated with Marshall guitar amps.
     
  4. hdracer

    hdracer Supporting Member

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    EH EL-34's are nice but my favorite is TAD EL-34STR
     
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  6. jastacey

    jastacey

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    My favorite 6CA7's are the Sylvania if you can find them
     
  7. RockBobby

    RockBobby Supporting Member

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    Thanks Bobby,
    I cut and saved and printed your advice about the resonance. It was just a fuse untill I cracked a tube getting it back in the case.

    I have two more questions.

    1) Can I replace the broken tube by trying to get a "close enough" match, and 2) if not, can I pull another tube and run 4 tubes until I can save for a re-tube?

    I have other amps to use so I'm not desperate.

    Thanks, Bob
     
  8. RockBobby

    RockBobby Supporting Member

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    Here is the tube value in there now.
     
  9. Bassmec

    Bassmec

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    Back when tubes were made by proper british chaps like George Mullard
    who had a couple of fairly useful pentode designs, one was the EL34 and the other was the EL37 quite a similar tube in most ways and since RCA
    where fairly devoid of any tubes that could do 25 watts, George sold the
    EL37 design to RCA because GEC came out with the very nice KT66 and George had already Improved the design of his EL 34 to attempt to improve LF performance calling it the FX2 variant. So RCA called the EL 37 a 6l6GC and the EL34FX2 as a 6CA7. Since that glorious time the sort of Johnny foreigner red under the bed types, your nice (if a little left wing for my taste) Senator Macarthy didn't think that highly of, has been trying to make these things recently.
    No quality control luck yet, though the rotten little commie pinkos.
    NOS is the only way to proper reliability.
    The OP is using a loudspeaker cabinet is he not, odd that you and he don't consider its design and driver size/count might be relevant to the LF performance and advice here.:bassist:
     
  10. RockBobby

    RockBobby Supporting Member

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    Thanks. Have many variants. V-4, Sunn 2000S, GK 800RM, Ashy ABM500, Berg NV215, Fender215, Eden 410, MM115.
    I know LF performance.
     
  11. BbbyBld

    BbbyBld

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    1. If you order the tube from us, you can get a matching one. Just give the sales person the matching number. I'm sure there are other places to do the same thing. You won't have to re-bias if you do that.

    2. Yes, but use the next lower impedance setting on the back, so if you have a 4 ohm cab, use the 2 ohm setting. If you're unsure about which other tube to pull, the owners manual contains a diagram that illustrates how the tubes are paired up. The tone won't be optimal. Don't break any more tubes dang it!:p

    With some of the cabs you listed, you should be able to get good low end. While you're working on the head, make sure the driver tube is a 12AT7.
     
  12. Bassmec

    Bassmec

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    So do I.
    you just about could not make less difference to the performance of your amp other than changing the mains cable for a solid silver one or something equally daft. The only discernible difference would be if you changed the output stage to an ultra linear design at the same time.
    Nos RCA or GE 6L6GC JAN would get your amp very slightly more low frequency performance and last ten years or longer if properly re biased.
    Changing the cab from one type to the next and or doubling the driver count can however change performance several dB in LF performance.
    :bassist:
     
  13. RockBobby

    RockBobby Supporting Member

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    It is. Gotcha. I'll call Tiffany tomorrow. Thanks AGAIN!!!
     
  14. RockBobby

    RockBobby Supporting Member

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    I got it soldered in and pulled one tube, so it's working good now. I noticed a few scorch marks on a few solder joints towards the power in ?? I don't know what that means except it looks like someone may have replaced a few resistors? I took caution and pulled and labeled the 2 yellow and one of the red leads so I could solder it without touching anything. I know I shouldn't be screwing around in there without knowledge of it but I felt safe enough with what I did.

    The value is 22 on the remaining tubes and I think PV labels them that way. They are JJs. It was going to be 1/2 the cost of a retube set to replace one tube with them, so I am just going to live with 4 of 6 tubes till I re-tube, unless someone has a single they can part with that they think will match.
    Eurotubes said they will send me a single but it would be a crap shoot and no warranty. I get that.
    Does anyone know what the 22 is? Is it MV? I know there are more values to consider but no way to know what they are.
    Thanks,
     
  15. BbbyBld

    BbbyBld

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    The 22 is the plate current in mA when the tube is running in JJ's test circuit that they use for matching. That way when you set the bias for a matched set, all the tubes are running equally hot so to speak and will share the load equally.

    You called Peavey's parts dept. and they wouldn't just sell you one tube?
     
  16. RockBobby

    RockBobby Supporting Member

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    Yeah, They would but it was a dollar less than 2 and that was almost 50% of a full set @ eurotubes.

    So I could ask eurotubes to pick me a tube that cold as 22mv?
     
  17. RockBobby

    RockBobby Supporting Member

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    Got some 6ca7 EH coming!
     

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  18. spankdaplank

    spankdaplank

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    On BbyBld's suggestion I put a set of (8) EHX 6CA7 big bottle tubes in my Peavey VB-3. The difference was almost like night and day. It was an expensive "fix", but it opened up the potential of this amp. I always felt that EL34's were ok for guitar but limited tonally for bass. I also tried a set of 6L6GC's and found the tone to be somewhat bland. Of course these tone discussions are very much subject to personal preference and tone goals.
     
  19. RockBobby

    RockBobby Supporting Member

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    He advised me the same, but I have been reluctant to put money into fixing the 250v fuse problem. It was taking out a power tube and blowing. I replaced the tube but it happened again. I can run it on 4 tubes with no problems, but the sound is as described. I am just gonna bite it and have it fixed properly. I am already at a loss but I can't let a nice usable amp sit.
     
  20. okcrum

    okcrum in your chest Supporting Member

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    Good call. I've run an SVT that way temporarily. JJ 6CA7 work for me in my homebrew head. 22 might be mu (amplification factor) if that's what you mean.
     
    Last edited: Aug 10, 2014

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