Cold bias in tube amps

Discussion in 'Amps and Cabs' started by Fuego, Jan 3, 2018.


  1. Fuego

    Fuego Member

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    I notice people saying that this amp or that amp comes biased cold from the factory. Why? Then those same people say to bias it hotter. Shouldn't it be biased the same way as the manufacturer does? My guess is current production tubes are crap and can't be run the way they used to? For instance, I HAVE TO bias my fryette 2/90/2 cold or tubes don't last more than 2 to 3 months max.Thats why it's been relogated to paper weight duty. Many say Fryette is awesome and Engl is bad, but my Invader 2 and ironball have always held up show after show. POS if u ask me. Always wondered. Thanks.
     
    Last edited: Jan 3, 2018
  2. bbaug14

    bbaug14 Supporting Member

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    Bias is personal preference, within the operating parameters of the tube of course. A hotter bias yields a bit more sizzle and will bring on the gain a bit faster, while a colder bias will be a little more open with less gain, generally speaking. The feel will be different too.

    As far as eating tubes, a hotter bias will slightly shorten tube life. For amps with a really high plate voltage (which I suspect your Fryette may have) you may want to look at the tubes Ruby makes for that. Or the JJ EL34Ls have worked well with high plate voltages in my experience. Vintage tubes also seem to handle higher plate voltages better.
     
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  3. Fuego

    Fuego Member

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    They're kt88s in the Fryette. The thing eats tubes fast fast fast. Engls keep on trucking though.
     
  4. Fuego

    Fuego Member

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    Funny thing is, at least to me, is my Vht(Fryette) Gp3 preamp sounds better thru the power amp of my Invader than thru the amp it was intended for. I guess I like el34s more.
     
  5. Tidbit

    Tidbit Member

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    When I finally had to retube my old marshall 2203, I experimented with different biasing. Cold bias left the amp sounding fairly lifeless. Kinda dull . It just didn't have the Marshall grind. When I biased it correctly, the amp really came to life. It had a lot more presence.

    I never overbiased it.

    Did you have the same problems with different brands of tubes. I was thinking that you may have gotten a bad tube. It happens sometimes.
     
  6. Fuego

    Fuego Member

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    Same brand tubes but 4 quads all went bad. Steve Fryette biased it himself. He never replaced any of the sets either even though some were less than a month old. When I mentioned tube quality and high plate voltages, he said people don't understand what they are talking about. He stopped answering my emails too. Hence the switch to Engl.
     
  7. Tidbit

    Tidbit Member

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    I'm no expert but if 4 quads of tubes went bad that quickly, something must be wrong with the amp.
     
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  8. Sirloin

    Sirloin Supporting Member

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    Please define correctly biased. What method do you use?
     
  9. Fuego

    Fuego Member

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    I thought the same thing. Fryette says it's fine. I sent it to him to investigate the issue.
     
  10. ken374

    ken374 Member

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    Some sound better hot and some cool, dsl def cooler !
     
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  11. CallEOD

    CallEOD Member

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    Marshall spec'd the JCM-DSL to be biased @ 90mv which is a tad high for me. I like 80 so there goes your Theory.
     
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  12. Tidbit

    Tidbit Member

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    I used the guide that came with this bias probe.

    [​IMG]
     
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  13. ken374

    ken374 Member

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    well dude my tech is very well known and respected here in MI and he set mine at 30 or so! I asked why he said its all preamp distortion! and wont sound any better! less heat less problems can occur! I tried it at 36, 30, 32 months later and the red sounded clearer warmer and less fizzy at a cool bias! boom! there's your theory. People always say there bright is because there set at like 40 or so! there you go again! I had a few guys on facebook cool theres down and they love it now!! whos right>>? marshall doesn't even know why they set it hot my tech said LOL
     
    Last edited: Jan 9, 2018
  14. CallEOD

    CallEOD Member

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    Thats 80 per pair. You should always bias in pairs.

    http://www.compu-bias.com/

    Bias should always be set in relation to plate voltage not just some random number.

    Buy one of these and thank me later.
     
  15. ken374

    ken374 Member

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    He said if the plate voltage for example is from say I cant remember but say 430 to 500, 30 to 32 is good. Email Dean Zink he has a web site he will answer more properly then I can
     
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  16. CallEOD

    CallEOD Member

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    No thanks im good ...
     
  17. fiveightandten

    fiveightandten Member

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    430 to 500 is a HUGE range. A tube running at 30mV at 430V B+ will be at 12.9W, at 500V, it’s at 15W.

    The plate voltage needs to be measured each time you make an adjustment to the negative voltage.

    The proper way to bias an amp is by measuring the plate voltage AND current draw, so you can get the static plate dissipation wattage. Do not exceed the manufacturer’s spec for this. It is different for different manufacturers.

    Each tube will vary slightly, depending on how tightly they’re matched. I measure them individually, and place them in the amp accordingly. You don’t really way the 2 hottest tubes of a quad on the same primary leg.
     
  18. ken374

    ken374 Member

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    Like I said I cant remember exactly I usually do mine at my girlfriends the PV is usually around the same give or take a few. So from 30 to 36 isnt a whole lot different but its smoother some and sounds better. Pinch harmonics were easier at 32 opposed to 36 and hairy sounding
     
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  19. Jr Deluxe

    Jr Deluxe Member

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    Fender started the whole thing and Leo wasnt looking for overdrive, distortion, gain just some sort of clear amplification. And he biased the tubes on the colder side so people wouldnt bring the amps back for repair cause a tube expired. In fact some tube sets lasted 10 or 20 years if the usage was indoors at home .

    Then Rock and Roll and some types of blues came along and players found they liked the od, distortion, gain and volume they could get by abusing the amp in diffetent ways including biasing way hot. Remember now we have 10 different ways to get fuzz. Pedals, preamps, gain mods and you can come up with the other 7. Back then in the beginning of the marshall years that stuff was a decade away. So biasing methods and attitudes are a leftover from the early days and you got 3 or 4 ways to measure and set the power tube bias depending on what sound and what line of thinking you follow. Class dismissed.
     
  20. EADGBE

    EADGBE Member

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    Too cold sounds weak. Too hot sounds muddy.
     
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