Newbie Tube Amp Standby Questions

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Kappy, Feb 18, 2006.


  1. Kappy

    Kappy Member

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    Can anyone tell me the purpose of standby on a tube amp?

    I typically turn the amp on (already in standby) and let it "warm up" for a couple to a few minutes before playing. This seems pretty much common sense. I also heard that when you're done playing, put the amp in standby for a few minutes, then turn it off. This triggers my next question. I always forget to turn the amp off and find that I've left the thing sitting in standby for anywhere from 30 minutes, to overnight (like this morning when I found my Rambler sitting there with its green light beaming at me). I've heard that's bad to do.

    Can anyone with the techie knowledge about amps dispell any myths about leaving an amp in standby?

    For clarification, I'm talking mostly about my Carr Rambler, but also a Rivera Jake.

    Thanks for any info!

    Dave
     
  2. Blue Strat

    Blue Strat Member

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    You're doing the right thing at startup, letting the tubes warm up before slamming them with several hundred volts on the plates.

    When turning the amp off, no standby activities are required. Just turn both the standby and power switches off when you're done playing.
     
  3. Kappy

    Kappy Member

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    Thanks for the answer, Blue Strat. That makes sense. I guess I can read up about the techie stuff behind standby in an amp book if I want to get more details about how it works, etc.
     
  4. K-man

    K-man Member

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    I always let the tubes warm up in standbye when I turn my amp on, but have never bothered letting it "cool down" when I'm done playing. Does that really do anything?

    I would think you'd go through tubes pretty quick if you leave your amp on all night.
     
  5. aleclee

    aleclee TGP Tech Wrangler Staff Member

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    No need to cool down on standby prior to shutdown.
     
  6. brad347

    brad347 Member

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    leaving your amp on standby shouldn't really wear out tubes significantly, I think. Other opinions? With just the heaters going but no high voltage to the plates I can't imagine that it would cause any significant wear.
     
  7. The Rocket

    The Rocket Member

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    So, leaving the standby switch always on and using only the power switch to turn the amp on and off, is the best way to do?

    Usually I turn the amp on and then switch the standby on after 30 seconds...is this bad for the tubes?

    Please let me know! Thanks!!!
     
  8. John Phillips

    John Phillips Member

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    It doesn't cause wear, but it does something else nasty called 'cathode poisoning' (or 'sleepy tube sickness'). This is a change in the chemical properties of the cathode coating caused by being run hot but with no current flowing, and eventually leads to it becoming less effective. It's very slow, and I certainly wouldn't worry about it over an hour or two... but maybe overnight.

    What I've never been able to find out is whether the effect is reversed when the tube is put back to normal operation - in other words, does it recover if you then leave the amp fully on (even if it takes the same sort of time period).

    The real difficulty is to decide when to turn off and when to put on standby if you're not going to use the amp for a while... there are three factors: if you turn it off, you cause extra heating/cooling cycles (which are definitely bad for tubes and possibly other components); if you leave it running (especially at the sort of high idle currents that many guitar amps have) you are continuously wearing the tubes; and if you put it on standby you're risking cathode poisoning. There's no straightforward answer...

    I tend to turn off if I'm definitely not going to be using the amp again within an hour or so, but leave it on standby otherwise, even if that 'hour' turns into two or three.

    No...
    ...that's correct. Like Blue Strat said, you need to leave the tubes time to warm up before hitting them with high voltages.

    (If by 'standby on' you mean 'sound on' - this terminology is confusing, which doesn't help. 'Standby on' and 'on standby' mean opposite things to me, but I've seem them used to mean the same thing as well...)
     
  9. Kappy

    Kappy Member

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    Thanks for another informative post. So I'm guessing there's no way to discern (without some type of expensive diagostic equipment) whether your tubes suffer from cathode poisoning and that the only way to know is to rely on your ears telling you that your amp no longer sounds as good as it used to. Or is there a way?

    Thanks!

    Dave
     
  10. brad347

    brad347 Member

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    cathode poisoning... very interesting!

    Mainly, I turn my amp on at the beginning of the night, then I tune, run cables, set up my pedalboard (if applicable) put charts in order, whatever, then when it's time to start the set I flip it "all the way on." Back on standby it goes for the set break (15-30 minutes) and this continues til the end of the night, when I flip both switches "off."

    In the "real world," this is really all you need to know!
     
  11. donnyjaguar

    donnyjaguar Member

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    Bzzztt!! Wrong answer. When shutting down, turn the amplifier to Standby and when it stops amplifying the instrument it is then safe to turn off the mains. This can be less than 3 seconds in the case of my Fender or as high as 15 in one of my other amplifiers. Largely governed by the amount of capacitance in your power supply & value of bleeder resistors (if present).

    Why? Simple, if you turn the filament supply off while there is still high voltage on the tubes you are running the risk of cathode stripping just as you would by turning the Mains on when the standby switch is in the Run position.

    DJ
     
  12. gearitis

    gearitis Gold Supporting Member

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    I was recently told not to ever use the standby switch on my JTM45. Supposedly it is very hard on the tube rectifier.

    I've been wondering about this myself. Why would the amp have a standby switch if it can cause problems?
     
  13. donnyjaguar

    donnyjaguar Member

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    This is interesting. When designing my latest monsterpiece ftp://ben_nevis:ben_nevis@206.210.107.171 (I'll have to post the updated pictures of the cabinet soon) I asked around about putting a standby/run switch when using a GZ34 rectifier and heard nothing back from the resident experts. This is not meant as a slight, there are some super techs/designers on this site and I got some great ideas for other aspects of my design. Anyway, I've since done some research and I was not able to find any minimum load specifications for this tube. Given tubes are generally considered to be more robust than silicon diodes, and there is no problem with the Stndby/Run switch when using them, I went ahead and put in this feature. It works pefectly fine. I did learn that it can be a bad idea if your amplifier has an in-rush current that would cause the GZ34 to exceed its design specifications when engaging the HT. There's a chart that shows minimum loads acceptable for given AC voltage, secondary DC resistance etc. I'm using a choke-input filter with the output section powered post-choke so the inrush is largely limited anyway - I'm not sure why every guitar amp isn't done this way as its commonplace for hi-fi amplifiers. Your JTM45, if the schematic I have is to be believed, is not wired in the same manner. The output section, and its filter capacitor, is prior to the choke filter. This could very well result in exceeding the maximum current specifications (albeit briefly) when you switch to the Run position. I doubt this would cause a failure in the tube, but I suspect it could reduce the service life so I'm thinking the advice you received was sound.

    Cheers!
    D-J
     
  14. The Rocket

    The Rocket Member

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    Thank you very much John! I'm asking because (as Gearitis said) recently I've been told by a tech that using the standby switch is tough for the tubes...basically he told me to leave the standby switch on "ON" position ALWAYS and he said to use only the power switch to turn on and off the amp... he says that if you turn the amp on and you leave it in standby mode, the tubes don't warm up and when you put the standby switch on "ON" position there's a rush of current that is very bad for the tubes....he suggested simply to switch the amp ON (standby and power together) and wait a bit before playing....

    I'm not a tech at all, but this "Standby switch is bad for the tubes"-thing sounds pretty strange to me...anyone else heard the same theory?
    Thanks
     
  15. donnyjaguar

    donnyjaguar Member

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    I should probably clarify that this Standby/Run is really much more of an issue with amplifiers using solid state rectifiers.

    Its not nonsense though. Being gentle with your tubes is always a good thing. My one amplifier is running on output tubes that are 50 years old (not NOS) and still going strong. Pictures to prove if you don't believe me. Now that I've mentioned it of course I've probably jinxed them and they'll die the next time I power up. ;)

    DJ
     

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