12ax7 Preamp V1 Tube Turned White - Buy: Yeah Or Neh ?

Discussion in 'Amps' started by Lamf77, Apr 20, 2019.

  1. Lamf77

    Lamf77 Well-Known Member Supporting Member

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    I was looking into a Blues Jr. One popped locally, at a really good price.
    However, seller says all it does is hum, and his reason is the V1 preamp tube has turned white.
    I read this happens when the tube looses its vacuum.
    I may just contact him and bring a tube...it may work. Only issue would be a chronic problem.
    What else could cause such a thing, and if a tube swap on the spot seems to get the amp working...buy or pass? Buy anyway?
    Thanks!

    ecface187f797f9898fdafc21bd4d23a.jpg
     
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  2. mozz

    mozz Well-Known Member Supporting Member

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    If the price is right, buy it, don't fix it for him. Also, watch the top center screw, they are known to short to the circuit board becuase they are too long. There are different versions, creme board, green board. BillM is the go to website for this amp, he has passed but the website is still going. Be sure the back cover is included, it is foil covered and stops the hum.
     
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  3. jimytheassassin

    jimytheassassin Well-Known Member

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    Ya it wont work like that! replacing the tube is a must and it will almost definitely resolve the "issue". The only thing is, if you fix it for him, make sure you charge the difference in how much he raises the price afterward. Hah. Or will he want to keep it then. If the price is right and all else looks good, I might just buy it sight on scene. The preamp tube having gone bad like that should have nothing to do with the amp itself

    Sent from my SAMSUNG-SM-G930A using Tapatalk
     
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  4. 50 amp fuse

    50 amp fuse Active Member

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    Depends on how much the seller is asking for it as is. Other than that then yes a tube that turns white is indicative of loosing its vacuum. What gets me is.. Why doesn't the seller just install a new tube to resolve the issue before selling it, 12ax7's are cheap. Sounds a little fishy to me. But yea I'd say bring a tube and try it. If the seller tries to juke you on the price take your tube and go home.
     
  5. Lamf77

    Lamf77 Well-Known Member Supporting Member

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    Good point. I think he is some dude....non musician and may not want to bother. He only wants people calling no email or text.....old school? May call....offer and check it out. How could I tell if the circuit board is shorted? Screw Mark's?

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  6. Mickey

    Mickey Gandalf the Intonationer

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    @mozz is 100% spot on about @Billm's website is the go to place for info on this amp. I miss Bill, he was a good guy!
    Billm came up with a pot full of mods for this amp that turns it from a good amp into a great amp.
    I believe his son has taken over the website and you can still get the mods there.
    Even if you have to pay a tech to do the mods, they are well worth doing.

    And I agree, do not take a tube with you just buy it as cheaply as you can. :)

    @Lamf77 ::: If you look at the first pic you posted in the OP, you will notice three screw holes across the top.
    The one in the middle screw is the one @mozz was talking about, for when you put the back panel on.
    Use the shortest screw for that as too long a screw could short to sumpthin. :)
    In truth, you do not want any of those screws to be any longer than they need to be.
     
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  7. RiverDog

    RiverDog Well-Known Member

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    My concern is, it looks to have all stock tubes with the exception of V1 so methinks he's already tried swapping it out. May be nothing but something to consider.
     
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  8. 50 amp fuse

    50 amp fuse Active Member

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    Generally you can smell if the magic smoke's been let out of a tranny or PCB. Other than that just a visual inspection for anything out of the ordinary. And I also agree that the V1 doesn't look stock. But the fact its white suggests it's cracked and lost vacuum. Coincidence? Easy and cheap way to change your amps attitude is by swapping that V1. Perhaps all that happened here is someone got a little too ham fisted while doing the swap.
     
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  9. mozz

    mozz Well-Known Member Supporting Member

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    Edit from before, i think the center screw shorts to the pot, not the circuit board. It was a known problem and was fixed on later models. Tube looks like the others, JJ? Sovtek, Groove tube?

    I think i'd go $150 non working.
     
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  10. andrewsrea

    andrewsrea Well-Known Member

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    Mike: I have never seen a preamp tube get cooked by a circuit problem, to the point it lost vacuum. I guess the cathode resistor or by-pass cap could short to ground, but I've never seen it and that would be an easy thing to spot. Normally these devices fail 'open' (no connection) vs. 'short.'

    Normally these go white from being banged around or sudden hot to cold temperatures (like a patron spilling a beer on your tubes - happened to me).

    Output tubes (the taller ones) on grid bias amps (negative voltage applied to the control grid) can go white if they were underbiased and running cherry red. Normally even that condition they will fail before breaking vacuum. These output tubes are fixed bias (cathode biased) and it would be like preamp tubes, rare for the circuits to cause this and it be chronic.
     
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  11. idiotsdelight

    idiotsdelight Well-Known Member

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    I'm in the "play stupid" camp. If you fix it on the spot he'll renege on the sale.

    That tube does look toasted. How much is he asking? Could be a great gamble.
     
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  12. honyock

    honyock Well-Known Member

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    definitely play stupid, I've now flipped two of these for 2x my money just by buying right, and reselling as is.

    Well worth the gamble if you are looking at under $150
     
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  13. Lamf77

    Lamf77 Well-Known Member Supporting Member

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  14. honyock

    honyock Well-Known Member

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    The Made in USA ones have a lot of things that need to be corrected, if it is totally original, to get the most out of it.

    My 1st was was a MIA version, I modded it and it still wasn't as good as my MIM one I don't think.
     
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  15. Mickey

    Mickey Gandalf the Intonationer

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    So? As @mozz suggested, offer him $150 and see how he reacts. After all, there must be something wrong with it because it turned the tube white!
    Tell him you'll have to take to an amp tech and who knows what it will co$t you to get it working???
    :)
     
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  16. mozz

    mozz Well-Known Member Supporting Member

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    No to $250. I took $150 off the top of my head as max. In the ad he states it has the green circuit board, you would only know that if you are familiar with those amps, or did a bunch of reading on it, therefore, if it was only a tube, why didn't he fix it? Price is now lowered to $100 due to "something's up".
     
  17. Lamf77

    Lamf77 Well-Known Member Supporting Member

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    Best save my GAS/Slush Fund reserves for the Peavey Classic 20 or 30. Thanks!
     
  18. idiotsdelight

    idiotsdelight Well-Known Member

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    I agree. Me thinks seller is withholding info. If he knows enough to describe the CB he knows/suspects why the thing is wonky.

    IF you still wanted to try be as nice as possible explaining your concerns & make an offer. After he's insulted you'll know why.
     
  19. Poodlesrule

    Poodlesrule Well-Known Member

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    Or, leave a number with seller.
    he or she may reconsider.

    The Classic 20 is nice!:sneaky:
     
  20. Mickey

    Mickey Gandalf the Intonationer

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    Did you buy it? The ad has been deleted?
     

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