Biasing El34's by Ear? Safe?

Discussion in 'The Workbench' started by pman, Jul 1, 2010.

  1. pman

    pman New Member

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    I have new El34's going into a 74 50W. I know that to properly bias an amp, a couple steps must be taken. After discharging the Filter Caps I am lost. I have a multi meter and a calculator but do not know what to do after discharging the FC's. If biased too hot could I ruin the OT? How about too low? I don't mind a little crossover distortion, but I want the amp to sound good. With the last set of Winged C's the plate voltage was at 470. Would this be the same at my home (not the tech's) with different tubes?
     
  2. pman

    pman New Member

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    911 amp tech over the phone: Learned B+ voltage, Ma readings, Pin 8 on PT's, adjusted trim bias pot 40 Ma-sounds great, will check tomorrow after playing for bias drift. Original Winged C's turned out to be bad batch.
     
  3. T-Bird

    T-Bird New Member

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    Hi.

    Good to see that You decided to bias the proper way, not by ear.

    While a seasoned tech could get the bias close enough by ear if someone pointed a gun at their head, doing so is pointless. IMHO anyway.

    Regards
    Sam
     
  4. RickyLee

    RickyLee Well-Known Member VIP Member

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    What I would like to know is:

    What is the deal with all these reports of bad batches of =C= EL34's on this Forum lately??

    Is that company having a quality control issue??


    :hmm:
     
  5. charveldan

    charveldan Well-Known Member

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    By ear doesn't work and is a retarded concept.:wtf:
     
  6. charveldan

    charveldan Well-Known Member

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    Tube depot is selling tubes rejected by specs called "factory seconds" or some shite, real cheap like 25 bucks a pair and people are having all kinna problems with them, then act completly dumbfounded when they redplate or don't bias properly.

    Rule #1: Never skimp on tubes.

    Rule #2: Don't forget rule #1.



    http://www.tubedepot.com/sv-el34-2nd.html
     
  7. Wilder Amplification

    Wilder Amplification New Member

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    +1,000,000,000,000,000

    I have no idea who the hell came up with this concept but it's simply retarded. Bias isn't THE ONLY THING that affects an amp's tone and certainly not the "be all end all" of your tone.

    How can you discharge the filter caps before biasing the amp when the amp has to be ON to bias it?

    Honestly, and not trying to insult your intelligence in any way but just from what you've described it really sounds like you need to be going to a tech for your own safety as well as your amp's. These things aren't "toys"...there's a good degree of knowledge required to properly and safely work on them. They're not something you want to be trying to be a "blind tech" on. I say this for your own safety and to ensure that your amp lives a long life. Take it to a tech.
     
  8. wkcchampion

    wkcchampion New Member

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    +1. It seems you really have no idea about the concept of biasing, what measurements u have to take and why, what to change etc...
     
  9. pman

    pman New Member

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    If I wouldn't have mowed all those lawns to save up for that 1st Marshall, if I would have started off with disposable Crates, yada yada...all my problems would have been solved. I when biasing the tubes, I know the amp has to be on. I just want to be safe. I have been shocked before. It's been well over 2 decades since owning my 1st 2203 and it's about time I learn how to start doing this stuff. It get's expensive...and I know it can be more expensive if I fudge the amp up. I will save the more complicated maneuvers for the techs. Meanwhile, I will try more biasing. I cried when 67 Blackburns fried in my bluesbreaker. I know it's dangerous. Being on a budget is too.
     
  10. charveldan

    charveldan Well-Known Member

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    I'm happy to pay my tech $40 buck to take the Zap for me.:hmm:
     
  11. Ken

    Ken Well-Known Member

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    Safety is a good thing, but if you KNOW the amp has to be on to bias it, then what led you to say you would discharge the caps?

    Ah, THAT explains it! :hippie:

    Seriously, you seem a little lost...

    Ken
     
  12. Marshallhead

    Marshallhead Well-Known Member

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    Some of the guys make it sound like it's a disaster to bias by ear.

    Hell, we did that for years, with no regard for tube matching, and our amps sounded fine. You just figured out which way to turn the bias pot to max the -ve voltage, turned it al the way in that direction, and played the amp. If it sounded gravelly and sputtery, turn the bias down until it sound good. If the tubes didn't redplate or overly glow when played hard, the job was done. To this day, if I try that and then check with a meter or scope, it comes up just on the cold side of "theoretically" perfect and hence perfectly safe to operate.

    Still better to do it right, mind you!
     
  13. MajorNut1967

    MajorNut1967 New Member

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    I'm a bit curious, how many people do you know that have had issues with these tube or posted here with Tubedepot seconds? And the URL you posted tells exactly why they are being sold that way and they do give 10 day to return them.

    And do you adhere to your rule #1? So can I assume you have some wonderful NOS Mullard XF1 big base tubes in all your EL34 amps?
     
  14. MajorNut1967

    MajorNut1967 New Member

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    You may have seen the thread I posted and the where two sets of =C= EL34's I had installed had issues and they were brand new ones. But I have to say it's my first experience with these =C= tubes.
     
  15. Wilder Amplification

    Wilder Amplification New Member

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    I too have tested out a set of =C= 2nds from Tube Depot. They lasted about 20 minutes before the suppressor grid in one of them shorted on it. Of course that was just one quad of them that I had so to make the definitive statement that all Tube Depot 2nd's are bad would be a misnomer.

    CP valves are not all bad. They're like anything else...there's always bad apples in every bunch. What we DON'T see is the reject rate of all the ones that are being rejected during initial factory testing or testing via the dealers/vendors. I'm sure they have their share of duds that they reject before they ever see the store's final inventory. But some of them will test OK, then fail within the first hour of operation in a player's amp. There's no way to 100% verify a valve's lifespan nor is there a way to 100% claim that NOS valves are any better than their CP counterparts as there is no way to prove a negative...the "negative" being the ones that DON'T fail...as there is no way to foresee the future.

    As for my JJ E34Ls, I've been running those in my purple plexi since earlier this year and I have yet to have one fail. My customer who owns the '72 Super Lead that I did the Dual Classic conversion on has been running the same set of Winged =C= EL34s that I installed in it with steady gigging duty since February and has not had any failures at all.

    Another test I've done was between the JJ E34L vs the EH6CA7. Amp cranked to shit on a Marshall Power Brake with a volt meter hooked across the screen resistor. Both valves at full crank had a screen current draw of 35-36mA, yet the EH 6CA7s seemed to exhibit a bit more screen glow than the JJ E34Ls did yet they were drawing the same screen current! The only thing I can conclude from that would be that the JJ E34Ls must use a heavier duty screen wire than the EH 6CA7s do and as such can tolerate the overcurrent/screen overdissipation condition much better than the EH 6CA7s. This is a very good thing as cranked to the max valve amps tax the screens more than anything else.

    Surprisingly both valves yielded a very similar tone, with the JJ E34L exhibiting a smidge more brightness and clarity than the EH 6CA7.

    Bottom line...with any valves it's always a crapshoot. You can't predict the future and as such there's no way to 100% conclusively verify that Brand X valves are going to last longer than Brand Y valves. In regards to valves sold as "seconds", there's a reason why they're sold as seconds and should be something you take into consideration when deciding to purchase them.
     
    Last edited: Jul 2, 2010
  16. charveldan

    charveldan Well-Known Member

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    SED Winged =C='s in my two Marshalls,[not seconds] , there were several threads on HC about "bad" factory seconds in the last week.
     
  17. MajorNut1967

    MajorNut1967 New Member

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    Oh ok thanks, do you know if they were from Tubedepot?
     
  18. cattystrat

    cattystrat New Member

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    As far as biasing by ear, if you read "Inside Tube amps" by Dan Torres he said he prefers to set the bias by ear. His reasoning is the ear will be the final judge as to whether the amp sounds good or not. Bill Webb of Austin Vintage Guitar uses the transformer shunt method and also a scope with a signal generator and he monitors the crossover notch. I know because i've worked with Bill and after all, he is Eric Johnsons amp tech. When i set bias i monitor all readings while i burn in the tubes. Grid voltage ,plate amperage draw and scope waveform. But still if you have all those things where they're supposed to be, does not mean it will sound good. But if you set bias by ear you really have to know what to listen for and what to watch out for. Not all people have that gift. On to the Winged Cs. I bought some of the factory 2nds form Tube Depot and as of yet, have no had any crater on me. Knock on Wood.
     
  19. Wilder Amplification

    Wilder Amplification New Member

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    Yes but he also checks things with a meter and scope to ensure that they're not running too hot either. The OP was referring to biasing STRICTLY by ear with no test equipment hooked up.

    The bias should be set for best tone without exceeding the electrical limits of things. This is how people blow shit up. The big name artists can afford to replace shit all the time...most average joe guitar players cannot so there's a big difference there. Everyone has this mentality that amps must be biased right at their 70% limit in order for them to sound good when more often than not this is not the case. I bet if you had the player play the amp in a blind tone test while you set the bias while monitoring the meters, the player would find that he likes a colder setting than he might think he does.
     
  20. charveldan

    charveldan Well-Known Member

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    I believe they were.
     

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