Troubleshoot my JVM

Discussion in 'The Workbench' started by Hard40sta, Oct 18, 2020.

  1. LPMarshall hack

    LPMarshall hack Well-Known Member

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    I googled some old MF threads that say they were discontinued.
     
  2. avspecialist

    avspecialist Active Member

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    I know I might be a little hot, I actually called The Tube Store told them my numbers, they thought they would be fine for their tubes. So far no red-plating, over the last month or so, just the best sound ever out of this amp.
     
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  3. Jethro Rocker

    Jethro Rocker Well-Known Member Silver Supporting Member

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    I got a Eurotubes bias meter. Same basic thing. Does 1 tube at a time. It was like 100 bucks. Shows PV and bias current. Still have to open up amp to adjust but hey, it's miles easier.
     
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  4. LPMarshall hack

    LPMarshall hack Well-Known Member

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    Serious question tho...

    so if you have to open up the chassis and adjust the little bias thingy anyway...what is the benefit of it?

    Is it doing something else for you that a multimeter won’t? Just trying to figure out how these things work as opposed to the “traditional” way...:cheers:

    edit: I watched some videos and it looks like the thing does the plate voltage and milliamps equation for you. All you have to do is adjust the bias pot to the desired tube reading. Is that correct?
     
    Last edited: Oct 19, 2020
  5. Shae201

    Shae201 Well-Known Member

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    Also, adjusting bias on one side affects the other. It's a balancing act to get both sides close to same DC millivolts.
     
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  6. Geo

    Geo New Member

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    You have to find the balance yes,but the voltage on the plate what has to do with the tubes adjustment,even its going up or down,i don't get it..(sorry but im new to this,just bought my first tube amp and im on the same way)
     
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  7. KraftyBob

    KraftyBob Well-Known Member Gold Supporting Member

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    I've not done this myself but figured it may be worth looking into for some.

     
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  8. Shae201

    Shae201 Well-Known Member

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    If at all possible, take it to a technician and see if they will let you watch how they bias. There are important steps to prepare for biasing that you need to know. It can be dangerous. Learning to read a schematic and knowing how the power section works by having someone show you is a great start.
     
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  9. Jethro Rocker

    Jethro Rocker Well-Known Member Silver Supporting Member

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    It beats taking MM probes and touching live contacts on tube sockets firstly. Simply plug in, heat up, I still do tye math quickly but it measures the PV and current. Easy peasy,no MM, no poking atound inside with probes.
     
  10. anitoli

    anitoli Well-Known Member Gold Supporting Member

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    I love the smell of arcing mulit meter probes in the morning...................:D
     
  11. anitoli

    anitoli Well-Known Member Gold Supporting Member

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    That exposed voltage thingy could be very dangerous. I would rather use a meter inside the chassis.
     
  12. LPMarshall hack

    LPMarshall hack Well-Known Member

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    But you’re still poking around the bias pot correct?

    Hopefully they’ll stay selling those again soon.
     
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  13. guitronics

    guitronics New Member

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    That is the best advice I have read...There were 3 guys quoting 3 different Bias voltages!
     
  14. Jethro Rocker

    Jethro Rocker Well-Known Member Silver Supporting Member

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    Yeah. Relatively way safer to turn a small pot w a screwdriver though, to me, than connecting meters to live sockets. It elimates those steps. Totally worth it to me. Eurotubes likely still does.
    I like bias points and adjustments on the outside better still.
     
  15. LPMarshall hack

    LPMarshall hack Well-Known Member

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    I need to get one. I called them and they said they should be ready for sale again in about 2-3 weeks.
     
    Last edited: Oct 20, 2020
  16. Jethro Rocker

    Jethro Rocker Well-Known Member Silver Supporting Member

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    I find it really easy. Esp when you have a few amps to bias here n there
     
  17. LPMarshall hack

    LPMarshall hack Well-Known Member

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    I also like that you can play the guitar while the thing is hooked up so you can tweak on the fly without disconnecting it.
     
  18. Jethro Rocker

    Jethro Rocker Well-Known Member Silver Supporting Member

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    Good point. I have done that to set by ear but know I am in a safe area of bias.
     
  19. LPMarshall hack

    LPMarshall hack Well-Known Member

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    I know you know good tone, Jet. So if you like this bias thing, it’s good enough for me.
     
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  20. Jethro Rocker

    Jethro Rocker Well-Known Member Silver Supporting Member

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    Thanks! Well it is convenient.
     
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