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Why use a tube for the rectifier?

Discussion in 'Amp Tech Center' started by MikeBee, Sep 13, 2020.

  1. MikeBee

    MikeBee TDPRI Member

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    Hi all,
    I have recently become fascinated with tube amps and no little about them. I googled rectifier to find out that it converts ac current to dc current, I used to know that.
    So that seems like a straight forward job. Why would a tube want to be used in that circuit?
    Also, any websites or books that explain theory and wiring for the tube amps? I can get rather obsessed with new to me technology that I find interesting.
    Thanks for the help, MikeB
     
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  2. NTC

    NTC Tele-Meister

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    1. Tube rectifiers existed before semiconductor diode rectifiers. Therefore old amps used them.
    2. Vacuum tube rectifiers have inherent resistance that is much higher than in silicon diodes. This leads to more variation in plate voltages in the amp as volume increases. It also lends a pleasing compression effect that leads to thecsinging quality of an amplifer pushed to its limits.
     
  3. Norris Vulcan

    Norris Vulcan Tele-Afflicted

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    The warm heart of the AC30.....:cool:

    Some say an SS rectifier is 'snappier', the attack is faster. But then the slower 'bloom' is one of the joys of inefficient old tubes.
     
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  4. schmee

    schmee Doctor of Teleocity

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    Tube rectifiers allow for some "sag" in the attack. A 5Y3 gives more, A GZ34 less. Additionally if you want SS rectification a $13 plug in can go there. Options
     
  5. Dan_Pomykalski

    Dan_Pomykalski Tele-Meister

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    I’ve read that tube rectifiers have little to no effect in single ended amps, but I notice more sag with my Champ than I do with my Deluxe Reverb (which has a 5U4).
     
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  6. Javier668

    Javier668 Tele-Meister

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    The sag thing
     
  7. jman72

    jman72 Tele-Afflicted

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    Check out Rob Robinette's website. It will teach you all the ins and outs of basic tube amp function and then some. Probably the best site on the internet for such things.
     
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  8. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    ss diodes are not pretty... A glowing bottle is a beautiful thing.

    As others have said, tubes add some nice nuances.
     
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  9. mrfitz98

    mrfitz98 TDPRI Member Silver Supporter

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    Some people call it bloom, I think it makes it feel "bouncy."

    '66 Tremolux
     
  10. LOSTVENTURE

    LOSTVENTURE Tele-Afflicted

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    Personally, if I'm looking for clean tones, then either SS or tube does the job. But if I'm wanting to get a little dirty, then the tube rectifier works better.
     
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  11. Peegoo

    Peegoo Poster Extraordinaire

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    Tubes aren't necessarily better than diodes for rectification...they just behave differently.

    Remember that many models of Marshall amp from the late 60s onward (and others), known for their tone and response, are diode rectified. Stevie Vaughan had some of his Fenders converted from tube to diode rectification (Cesar Diaz did most of the work) to improve the punch and low-end clarity.
     
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  12. Paul G.

    Paul G. Friend of Leo's

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    As others have noted, older designs use tubes because it is older tech.

    As far as bloom and sag -- In any class A circuit the amp is pulling full current 100% of the time, so no sag in single-ended or true class A amps. So, no your Champ isn't "sagging".

    In class AB amps (99% of them), you only get bloom or sag if the rectification is inadequate or if you're cranking the amp. At moderate volumes you are not getting that "bloom" or "sag" due to rectification unless your amp is a cheap or poorly designed model. So the guys playing their Deluxe Reverbs with the volume on 4 or 5 talking about the glorious sag they're getting are confused.

    Either method of rectification is fine. If you didn't know what kind of rectifier an amp has, you wouldn't know what kind of rectifier it has by playing it.

    In my opinion.
     
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  13. Dan_Pomykalski

    Dan_Pomykalski Tele-Meister

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    Yes it is.

    In my opinion.
     
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  14. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    You'd seen Fiddler? TRADITION!
     
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  15. tubeswell

    tubeswell Friend of Leo's

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    With single-ended amps running in Class A operation, the output tube is conducting throughout the entire signal cycle, so load current is 'almost constant'. While you can theoretically get 1.5X at maximum current draw, the (in)efficiencies of SE amp circuits mean that - apart from a little extra screen current when the output stage is being hit with a big signal - there is not a lot of difference between the amp running under low signal and the amp running under big signal. It's typically about 20% maximum increase in current draw in your average Fender Champ at full blast (if that)

    But if you have a lower-efficiency tube rectifier (like a 5Y3 instead of a 5AR4), and/or if your tube load current is greater (e.g. a 6L6 instead of a 6V6 etc), or if the power supply is in some other way inefficient (like if your PT has poor load regulation), you will be more likely to notice some sag at higher power, even in SE Class A.

    With PP amps operating in Class AB1, you get bigger changes in current draw under heavy running conditions (because the screens in the 'off' tubes continue to work hard in the B-loadline part of the cycle, alongside the plates conducting harder in the on-tubes working into the lowered load resistance) so you notice the sagginess more with tube rectifiers. If you hit the signal hard with a fuzz pedal in front of the amp, you notice it even more.
     
    Last edited: Sep 14, 2020
  16. 24 track

    24 track Doctor of Teleocity Ad Free Member

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    all tube amps have their historical beginings with one amp design used in radios, Fender , Doc Kaufman and the boys used that design as a base for first amps, at that point in time discrete devices did not exsist, Marshall used the early Bassman circuits to design his amps , so the whole tube amp genre is a hybrid of a basic design useing available technology , tube rectifiers were readily available at the time so to be cost effective they used them ,( not to mention surplus military supplies were readily available ).

    the first SS amps were too clinical and lacked body but the technology was moving forward to allow for solid bridge rectification and multiple gain stages , now bring in the purists who want solid tube tech the way it was made in the past ( I have a love for BF super reverbs early 60's complete with a 5UA4 rectifier)

    there is a percieved marked difference in the tonal texure of a tube amp , that a hybrid , or SS cannot match. Some times the breakup just before a tube fails gives an increadable tone thats hard to match, but with all things original an old amp has had the crap played out of it and the components fail , by replacing the caps etc the amps are no longer original.

    just my opinion , but it dont mean squat!
     
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  17. RadioFM74

    RadioFM74 Friend of Leo's

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    As all the others said: guitar amplification is a business that started (in earnest) in the 1930s, and back then tubes were the ONLY technology available for that job. When diodes became available, amp builders (Fender first of all) promptly integrated SS rectification in their "premium" amps.

    The idea that tube rectification is better – indeed, the fact that it still exists as an industry standard – is a prime instance of what a conservative bunch we guitarists are (myself included).

    I thought I heard some difference between a '65 Bandmaster and what became my '64 Tremolux, and chalked it up to rectification. But once I booked a rehearsal room that had a Mesa Dual Rectifier ONLY to test this and as @Paul G. noted, at less than ear-splitting volumes I could not discern any difference in feel or sound when flipping between tube rectification or SS rectification…
     
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  18. ballynally2

    ballynally2 Tele-Holic

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    some amps have both options. That's great because sometimes you need a certain tightness, especially on bigger stages and/ or outdoor venues.
    My Frenzel has that PLUS the option of cathode and fixed bias and nfb options.:)
     
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  19. Fluddman

    Fluddman Tele-Meister

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    Why use a tube for a rectifier? To increase the chance that the amp won't work at the next gig?

    In my experience a tube rectifier is the most likely part to fail. So using a solid state rectifier makes sense in terms of reliability.

    In terms of sound I can't really tell the difference. But given the choice I'd go with a tube rectifier.

    Can't really explain why - just like having that extra glowing orb.
     
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  20. mojek

    mojek Tele-Meister

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    The volume sag starts usually with volume about 10-11 on 5E3 deluxe. Or check Brian May vid, where he explains the AC30 sound. The tube sag starts usually at 90% of volume. As was already sat, the lover volume drop on rectifier, the lower sag. 5U4GB and 5Y3 will sag nicely, GZ34 less and Si diodes not. However, it´s best to play/try to play such an amp yourself, since the tube sag effect is much more intense, than just hear it.o_O
     
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