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Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups

Variations in sag due to rectifier tube. Specific question.

Discussion in 'Amp Central Station' started by gmm52, Oct 5, 2017.

  1. gmm52

    gmm52 Tele-Meister

    Sep 23, 2016
    Southern Ontario
    Some reading indicates that various brands of rectifier tubes (within a given model, say GZ34) may cause a change in tone (on the dynamic side of things) due to changes in sag. The question is, would these variations only manifest at high volume, i.e., when the amp is pushed hard? Or, would any differences also appear if the amp is played at modest levels? The reason for asking is because I rarely open this amp up, and would not bother experimenting with different rectifier tubes unless I might find some variation at my relatively modest playing levels.
  2. W.L.Weller

    W.L.Weller Tele-Meister

    May 20, 2014
    The short answer is no. Don't bother swapping rectifier tubes if you're only using the first 25% of the amp's volume knob.
  3. CV Jee Beez

    CV Jee Beez Tele-Meister

    Nov 24, 2016
    Duarte, CA
    I've had 2 different NOS rectifiers in my Supro and did not perceive a tonal difference. I'd say a differnt brand of the same type wouldn't really show up tonally. Hope this helps.
  4. Dacious

    Dacious Poster Extraordinaire

    Mar 16, 2003
    Rectifier tubes of the same sort are either on or off. Reliability and longevity is a factor but actual characteristics can't vary much. IOW if I sell you a GZ34 it better damned-well behave like one and measurably so. It has only one function, to turn AC voltage into - - - - - so that can be turned by the big filter caps into ------------- DC voltage. If you get 420 volts out of Brand A, Brand B better give you +/- a few volts.

    A GZ34 is a relatively high efficiency, low resistance 'fast' tube. Of course modern solid-state diodes are even more so. If you get power supply sag it's more likely to be the power transformer giving it up.
  5. homesick345

    homesick345 Poster Extraordinaire

    Jan 20, 2012
    Beirut, Lebanon
    No swag to speak of from GZ34. Practically rise times equal that of silicon
  6. PC_Hater

    PC_Hater Tele-Meister

    Aug 13, 2013
    The first reply is the correct answer, save your money. I tried to quote it but failed!

    ALL vacuum tube rectifiers have sag. The more current you pull from them the more sag you get. The sag increases as the tube gets older.
    A quick search on the internet found the specification sheet of the GZ34 from September 1958.
    It has graphs of Output Voltage vs Output Current with different input voltages and different conditions.
    The output voltage sags about 50V at 200mA output at 400V and the tube is putting out 80W of power.
    The 'speed' of the response for your guitar amplifier really doesn't matter.

    Knowing that sag occurs you now also know why 'dual rectifier' designs are made where you can switch between tube and solid state rectifiers. You will notice the difference when playing loud - but which would you prefer? Decisions decisions...

    Over 40 years ago I had to do a full mathematical analysis of various rectifier circuits under different loads during the 1st year of my BSc Electronic Engineering. Tubes were still taught back then!
    Last edited: Oct 5, 2017
  7. telemnemonics

    telemnemonics Doctor of Teleocity

    Mar 2, 2010
    For a change in the amps performance to result from changing between two rectifiers labeled the same, there would have to be a spec difference, which would require one of the tubes to be inaccurately labeled.

    Take the GZ34 and there were some Sovtek brand in a very small bottle that were supposedly not a true GZ34. This was early in Sovtek imports AFAIK and not commonly found. There are still small bottle Sovtek GZ34 that are correct spec AFAIK.

    Take the 5u4, 5u4g, 5u4gb, 5u4wgb; those are labels off the top of my head (IIRC!) and most are different from one another, but some may be the same as one another. Assume they are interchangeable and one may find differences in the amps performance.
    I have half a dozen 5u4 with the writing barely legible. Not sure they are the same.

    WRT when you might notice a difference, it might be correct to say it will only be noticeable at high volume, but the question presumes that you are comparing two tubes of identical spec.
    So it's kind of redundant to ask or answer: will the same tube sound different at all volumes, or only at high volume?
    The same spec tube will sound the same regardless of brand or volume.

    Then we get into substitutions.
    If you consider tubes that are acceptable substitutes to be in the group that is "the same", then you will be more likely to hear a difference, because "acceptable subs" are not the same as "the same".

    WRT when will you hear a difference if the tube is different, IME it is harder to hear small differences, but you can hear it at all volumes, not just when sag is happening. Sag is not the only sound influence of a rectifier tube.
    Even at idle, there can be a 50v difference between one rectifier and another.
    Higher voltage means more volume, punch, treble and bass.
    Lower voltage means less volume, less punch, less clarity, less treble and bass, but what you might call a fatter warmer tone.

    A small change in voltage will be hard to hear, but so can a small turn of the treble knob. A change is a change whether we notice it or not.

    But not many amps can use that wide a range of rectifiers.
    I have an 18w Marshall variant that can take everything from a 5y3 to a gz34, and that swap is very noticeable, even at low volume.
    In fact the amp sounds harsh and stiff at low volume with a gz34, but sweetens up nicely with a 5y3.
  8. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Ime, a change in the voltage supply level will change the sonics at every volume level. This will/can occur no matter if one replaces one certain tube of a certain model with another tube with the same designation. With old stock tubes, the difference between one tube..say a GZ34...and another GZ34 might not be enough to yield a different B+!; but with modern tubes, a GZ34 from one manufacturer may well yield very different voltages than does a tube from another manufacturer.
    telemnemonics and Andy B like this.
  9. PC_Hater

    PC_Hater Tele-Meister

    Aug 13, 2013
    Changes in supply voltage are easily dealt with. Buy a Dual-on-line voltage UPS. No matter what comes in it WILL give 110Volts out!
    (Or 220V for those of us that live in countries that made a better decision on what the mains voltage should be!)

    Sag is not the only sound influence of a rectifier tube.
    Even at idle, there can be a 50v difference between one rectifier and another.
    end quote

    Then the tube is not to spec is it?
    The output from a batch of rectifier tubes won't be accurate to 0.1V but 50V? I doubt it.
    And if it IS true, fit a silicon rectifier.

    The most amusing thing about this is that a rectifier is a two terminal device.
    That means you can 'model' it really really easily so your rectifier can be anything from a GZ34 to a heavy duty silicon rectifier just by turning a knob.
    And NOBODY will be able to tell if it is a gunuwine tube rectifier or not!

    None of the specs I have found give a tolerance on the voltage output, but again, 50V is damn near a 10% difference, and I doubt it.
  10. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    By 'supply voltage' I was speaking to the B+ that the PT and the rectifier are yielding.....assuming that the wall voltage is 'correct' for the amp. to the wall voltage, 110VAC is not what a lot of amps want to see. Maybe the old tweeds. By the mid-1960's, 117VAC was the standard.
    The heater filament voltage is a good measurement of what a PT and the wall voltage are doing.....if the heater filament voltage is correct, then the amp will/should being seeing the B+ that it was designed to see.....given a correct rectifier.
    Since we are on the subject of tube rectifiers.....I was doing some preliminary diagnosis on a Matchless HC-30 which is blowing fuses. Why would anyone pay that kind of money for an amp and run a cheap modern GZ34 in it???
  11. xafinity

    xafinity Friend of Leo's

    Dec 24, 2015
    my Mom's basement
    So many learned thoughts on rectalizer options. I'm always impressed.
    Seriously all the years I never gave it any thought until the internet when I leaned to be skeptical until I could try it myself.
    I have a feeling results might vary greatly between players.
    Last edited: Oct 5, 2017
    t guitar floyd likes this.
  12. mherrcat

    mherrcat Tele-Holic

    Dec 12, 2013
  13. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Different results occur between different rectifiers.Opinions as to differences in sonics vary among the players according to what their ears hear. The first of these two situations is measurably objective. The second one is subjective.
  14. Tomm Williams

    Tomm Williams Tele-Holic

    Jun 11, 2016
    Of all the amps I own, my very favorites happen to be tube rectified. However I don't know if they sound that way BECAUSE they are tube rectified?
    I've read numerous informed opinions here that would leave me to believe the tonal differences are not that significant (if any)
    Maybe it's just coincidence in my case and there are other factors at play.
  15. Old Tele man

    Old Tele man Friend of Leo's

    May 10, 2017
    Tucson, AZ
    Those "rise times" can change (drastically) with differing configurations (cap input vs. choke input) and with capacitor sizes and resistive (choke, etc.) loads.
    Last edited: Oct 6, 2017
    Wally likes this.
  16. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Tomm, ime, it is interesting and instructive to sit with an amp that has options for rectification. There is a definite difference between even a GZ34, which is as close to solid state rectification as a tube can get, and solid state rectification while all other aspects of a circuit's components remain constant. Voltage supply level and how it is supplied determine the feel of an amp in almost all situations.
    That is why I posted this...
    Ime, it is futile to debate with someone that something like a change in rectification UNLESS the debate contains an actual sonic experiment that can illuminate the point. I have many times foung folks who say the 'cannot' hear a difference in many aspects of guitar and amps....until that difference is exposed to them and they actually listen carefully.
    For instance, I have had people tell me that they were tone deaf....and then I do a little exercise using their ears to prove to them that they are not in reality tone deaf....regardless of what a choir director told them in one situation. They could recognize pitch and note small differences in pitch when they were given the opportunity to listen in a critical, discerning manner.
    telemnemonics likes this.
  17. PC_Hater

    PC_Hater Tele-Meister

    Aug 13, 2013
    Running an amp at low volume and switching between the tube rectifier and the silicon rectifier will yield the following results: the tube rectifier drops the voltage to the power tubes by 25V or more. The silicon rectifier drops it by 2.4V or so.
    I have never tried it, but the experiences listed here imply the silicon rectifier will sound brighter.

    Now crank the amp up.
    The tube rectifier becomes part of the tone circuit as the voltage to the power tubes drops by 50V or more. The harder you drive the amp the more the voltage to the power tubes drops.
    Fit a silicon rectifier and that drop is still 2.4V or so. (Assuming the idiot that designed the circuit did it right... )
    That voltage drop as you drive the amp hard is either a thing of joy to your ears or a definite WTF?

    And still, for the OP, save your money, you are not pushing your amp hard, you will need bionic ears to notice any difference.
  18. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    PC_Hater, I have an amp that will go from tube to SS rectification. I do not disagree with your numbers. I must, however, have bionic ears because I hear differences at any level of 'push'.
    IMe, listening is an art and a skill to which one must apply one's self. Some differences don't slap you in the face, but that doesn't mean that there are no differences. There are aspects of the signal that have nothing to do with sag but which change with a change in voltage.
  19. telemnemonics

    telemnemonics Doctor of Teleocity

    Mar 2, 2010
    When i stated that there can be a 50v difference even at idle, it was after stating that I was now talking about subbing different rectifier tubes.
    In amps that can use both a 5y3 and a gz34, that is about what the voltage difference can be, depending on the amp.

    @Wally pointed out that new production gz34 can vary a lot in actual spec, which I didn't know was still happening. My reference to early Sovtek gz34 being way off spec was the limit of my knowledge about wrong spec new production gz34 tubes.
    I'm glad to know this now, though I have a really hard time forking over the price of good old stock US and UK made gz34 tubes.

    WRT to tube rectified amps sounding "better" to a player, I'd guess that it has to do with the whole amp design ethic, and IME there are amps with much of the tube rectifier character due to other design aspects like inadequate filtering, cathode bias, low plate voltage, and in the case of distortion amps, there may be some sag/ compression in the preamp.

    But if the tube rectifier is part of what makes an amp sound like you want it to sound, you will probably miss it when subbing a SS plug in.
    Unless you like the sound but with it was a little tighter and brighter.
    We all might listen to a different part of the whole "sound".
  20. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    telemnemonics, admittedly my experiences with 'odd' GZ34's was some time back and was with those Sovteks which were perhaps rebranded 5Y3's, right?

    Re: that Chinese Ruby GZ34 in the HC-30 Matchless. It barely tests in the "?" range for emissions.....not good enough for my purposes. I pulled out a UOS Amperex that sent the emissions needle way on up the dial. When I get some power tubes for it...since one of the tubes is dead...I am going to see what the Chinese tube does with regard to voltage. I will compare that to the Amperex, some UOS Mullards, and some NOS Sylvania 5AR4's I have.
    telemnemonics likes this.
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