Any Other Better Bias Meter Than Weber Bias Rite??

Discussion in 'The Workbench' started by jalexquijano, Jul 29, 2016.

  1. jalexquijano

    jalexquijano Member

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    Just bought a Weber Bias Rite and two of the head probes cracked. Customer service does not reply promptly. Any other bias meter superior to this Brand which can measure the bias more precisely. This device doesnt even show the negative sign on the voltage reading!
     
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    The best way to bias an amp is
    Oscilloscope, load resistor, sine wave generator.
    You look at the wave form and make it hot enough to eliminate crossover distortion before power amp clips.
    The crossover distortion should show up just after the amp starts to clip at full output power...or even later (hotter).

    The O scope method is far more accurate...and this is how the factory biases amps.
    It confirms that the amp is working correctly (passes clean sine wave to full power rating)...something that a bias meter will never do.

    I think that the "formula" people are using to set bias current is - actually a lot of assumption and hogwash.
    Because: they never confirm the waveform...and they assume that it's working right.
    Something that a pro technician (or factory) would never do.
     
  3. jgab

    jgab Active Member

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    So if you had an amp that was working correctly, would the amp sound different using a scope versus using a bias probe? I don't have a scope, but I would like one someday. Recommendations?
     
  4. Petri358

    Petri358 Well-Known Member

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  5. Micky

    Micky Well-Known Member VIP Member

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    I use a Fluke Digital Multi-Meter.

    Can't get any more accurate than that...
     
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  6. jgab

    jgab Active Member

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    Micky likes this.
  7. Gunner64

    Gunner64 Well-Known Member Gold Supporting Member

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    The bias probes that ive had all had the 1ohm precision resistors in them. Id think any of them would work with any multi meter.
     
  8. Gunner64

    Gunner64 Well-Known Member Gold Supporting Member

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    I bought a dual probe with digital meterbox from a guy on ebay for 50 bucks that works very well. He makes them himself. He's on the east coast. Doesnt have the negative symbol either, but does it have to? It measures plate voltage too. Much cheaper than others, and works great. Ill post a pic when i get home. I always used the 1ohm resistor method on my amps. But when I started retubing and biasing friends amps, it was more convienient as most didnt have the 1ohm resistor from 1-8 to ground.
     
  9. Gunner64

    Gunner64 Well-Known Member Gold Supporting Member

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    On the subject of biasing with a scope. No doubt the oscope method is the most accurate way to bias, and Im not arguing that. AMS, you are more knowlegable than I on amp repair and maintenace. But ive heard stated (and can attest) that most marshalls are biased cold from the factory, and sound best with a hotter bias. My question is If the factory biases with a scope why arent the amps already biased at a perfect operating setting for their design?
     
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  10. MarshallDog

    MarshallDog Well-Known Member Gold Supporting Member

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    Nope!!!! Hands down the best IMO and based on experience! I have had mine about 7 years or more with no issues at all. There is no other meter out there that Incould find that will allow you to hook up to ALL 4 TUBES at once and instantaneously let you read voltage and current with the flick of a switch.
     
  11. HAMPAMP TUBE AMP SERVICES

    HAMPAMP TUBE AMP SERVICES Member

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    You brought up a good question. Amp companies do set their amp's bias to the correct setting for their design parameters (or most do anyway), this may not be the setting that produces the most headroom or even the best tone for you, but there is a point where running an amp too HOT puts a strain on the tubes, transformers, screen resistors etc.... The parameters that a company sets are designed to keep the amp in service, otherwise, it would be foolish to offer a warranty. Bias is a subject that will always bring disagreements to the table, it is always a matter of personal choice as to where it is to be set and what method is used to set it. There is an upper limit that can not be exceeded without causing damage to the tubes and/or amp circuitry. The closer you get to this limit, the quicker the parts will wear out and eventually fail but your amp will sound amazing right up to the point of meltdown. I usually set the bias to what most (those that cling to the 70-75% dissipation rule) would consider a little cold, I've never had anybody complain about the tone of their amp. Anyway, there are probably other reasons for companies to bias amps cold but I would assume that reliability would be one of the main factors in the equation
     
  12. jmp45

    jmp45 Well-Known Member

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    I have an Iwatsu 5705. There is an 5802 on the bay.

    http://www.ebay.com/itm/IWATSU-ELECTRIC-LTD-SS-5802-3-Trace-Digital-Storage-Oscilloscope-/330973502344

    5710
    http://www.ebay.com/itm/IWATSU-SS-5710-OSCILLOSCOPE-60-MHZ-/351668822454

    I've been using the Weber Bias Rite for years. Planning on schooling myself this year using the scope. I have an Eico 377 sine gen, good there too.
     
  13. Matt_Krush

    Matt_Krush Well-Known Member

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    Bias King...and a Fluke DMM.
     
  14. pedecamp

    pedecamp Well-Known Member

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    Im gonna post you a picture of my o-scope, you've mentioned many times this is the best way to bias an amp, I have no idea how to use one it was a hand me down from my dad. Maybe you can show me how to use it, I actually have two but one doesn't work it got burned years ago connected to an old tv that was hot my dad was working on.
     
  15. neikeel

    neikeel Well-Known Member

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    From a previous post:
    "I am too lazy but if needed............a method picked up from Duncan's Amp pages.
    Use a signal generator to deliver a 100 - 200mv, 600 cycle sine wave signal to the input of the amp (Sig.Jenny you can download on line is what I use). Use the volume control on that channel to vary the signal to the output stage.
    Set all the the tone controls at their mid-point.
    Using the load resistor (mine is 16ohm but depends on your amp selector options) scope is hooked up across the resistor.
    First set your bias pot to the highest negative voltage you can get at pin 5 of each output tube.
    Taking the usual precautions (one hand in pocket etc switch amp on and allow it to warm up and become stable).
    Then adjust the volume to get a nice clear sine wave on screen the frequency needs to be so that you get at least 2 full cycles on the screen.
    The sine wave will have a horizontal "notch" on the gradient parts portions of the wave around the crossing point of the y-axis.
    If you put too much signal through the signal will 'clip' ideally you want get a clipped signal and then just back off until the waves are complete and round, not clipped.
    Now reduce the negative bias voltage until it clips again. Trim the volume again until the sine wave cleans up and continue. You then continue reducing the bias voltage and adjusting the drive signal level until the sign wave is smooth on the sides.
    That should be it.
    Some tubes are easier to do than others on some it is hard to see when the notch effect disappears."

    Having said that I do not use this method routinely myself (as I said above) so if anyone disagrees with the method or can describe it better please feel to shhot me down - I will not feel precious about it
     
  16. MarshallDog

    MarshallDog Well-Known Member Gold Supporting Member

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    That's great tech info and I always wondered how to bias an amp using an O-scope BUT the Weber is just so dam easy and simple and I guran dam tee no one can detect any tone Differance between a Weber bias and an O-scope bias! They are both great methods and so similar in results. I could not when my amp Tech biased my amp via O-Scope then I re-biased it with my Weber.
     
    Last edited: Jul 20, 2020
    Dane12 likes this.

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