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Standby switch vs. leaving amp in run position vs. turning off

Discussion in 'Amps and Cabs [BG]' started by Jim C, Jan 23, 2021.


  1. Jim C

    Jim C I believe in the trilogy; Fender, Stingray, + G&L Supporting Member

    Nov 29, 2008
    Bethesda, MD
    Searched here and the web and find so many different opinions on tube amps and standby switches.
    I gather it is good to place the amp in standby mode when switching the power on or off. What about between sets or if the amp is not going to be used a few hours later?

    I was taught that the amp should be placed in standby whenever it was at rest and not being used. I was also taught that it was less stress on the tubes to leave the amp on and in standby even if you were taking a break for a few hours (as opposed to turning it off and then back on).

    Looking for some science on this one from techs and engineers. Amp in questions is an SVT-CL.
     
  2. Bent77

    Bent77

    Mar 6, 2013
    Colorado
    EatS1stBassist and fleabitten like this.
  3. FunkHead

    FunkHead Supporting Member

    Mar 10, 2007
    "it actually is not good to have the tubes on a very long time in standby, which is a fact from the RCA tube manuals.
    1. Only use the standby switch when warming-up of the amp

    Don’t use it as a “beer break” switch. For short breaks, simply turn down the volume control (or mute switch if you have one) and don’t use the standby switch, so there is not that nasty pop in the house sound system that could damage speaker drivers. If the time between sound check and performing is longer than 20 minutes, turn the amplifier completely off. You only need 5 minutes at the most to completely warm up a tube amplifier.

    2. The standby switch was only necessary when Leo Fender was designing less expensive amplifiers

    It’s as simple as that. Why else would you use something that often pops loudly in the audio when used, By the way, other brands did not use standby switches until Marshall copied Fender’s Bassman amplifier design and after the two biggest makers used these standby switches, everyone assumed you always had one on a guitar amp. Often, designers put these on amplifiers only because the public asks for them, not that they are needed. This is due to the power of the myth! These days we have other devices available to protect the capacitors and in general capacitors are much cheaper now and can be made to run at higher voltages without great cost.

    3. Don’t worry if your tube amp doesn’t have a standby switch, it doesn’t need it!

    Don’t put one on your amp because you were told it makes the tubes last longer! Is there a way to help my tubes last longer you say? The correct understanding of vacuum tube operational specifications prove there is no evidence that a standby switch can make your tubes last longer and actually could only hurt them if you overuse the standby mode."
     
    Last edited: Jan 23, 2021
  4. Jim C

    Jim C I believe in the trilogy; Fender, Stingray, + G&L Supporting Member

    Nov 29, 2008
    Bethesda, MD
    I didn't find much useful information in the guitar.com video; more just restating the info we have all read without an explanation. The thread is 90% opinions (which differ) and many not connected to the direct subject matter. Lastly, I have not found any info on when to turn an amp off or put in standby mode if it won't be used for an hour or more.
    I've been using tube amps for 40 years and have heard and read all of the opinions. Really interested in hearing from service techs and engineers as to the why behind it all.
    Can I also assume that this is really more about power tubes than preamp tubes? All the techs I've worked with in studios always said to keep everything on, even over quiet weekends in recording studios to include the tube Pultec EQ's.
     
    fleabitten and Wasnex like this.
  5. FunkHead

    FunkHead Supporting Member

    Mar 10, 2007
    Neither, It was to protect Capacitors.
     
  6. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Really? Care to explain how this is true?
     
  7. FunkHead

    FunkHead Supporting Member

    Mar 10, 2007
    "Leo Fender adopted the standby switch design from reading vacuum tube service manuals. He was self-trained in electronics and developed his own designs. Basically, his switch disconnects the high voltage from the circuit, but the big question is why?

    Leo Fender did not intend them for use during beer breaks as a mute switch (the biggest myth of all), even though this is what everyone thought he meant by the “standby” switch label and used them this way! A “mute” switch is a common switch often used on audio amplifiers but never designed the way Leo Fender’s “standby” switch is wired to the high voltage. A mute switch simply connects the audio signal to ground, stopping it from passing through the amplifier, just like turning the volume control all the way down.

    I should note the term “standby” has been used occasionally in place of the word “mute” on other switches that actually are audio “mute” switches for taking breaks, further adding to the public confusion. All guitar amplifier companies are infamous for incorrectly labeling or coming up with cute names for a switch’s function. Leo Fender also is known for mislabeling what technically is a tremolo circuit control as a “vibrato”. This is probably because he did not know how to play guitar? Maybe he could have come up with a better name than “standby” that is less confusing? Too late now I guess!

    The addition of standby switches on tube amps is accredited to Leo Fender.
    It’s not for protecting tubes

    Leo Fender did not use the standby switch to protect the tubes, because it actually is not good to have the tubes on a very long time in standby, which is a fact from the RCA tube manuals. There are so many people who get this part wrong. Beware advice given by some internet guru who was just regurgitating someone else’s myth that sounds technical, but is just wrong!

    This myth started with a misunderstanding of the old RCA tube manual recommendation for using standby switches when running very, very high voltage radio station transmitter tubes. RCA was NOT talking about the tubes used in a guitar amplifier. The tubes used in guitar amps are the same type tubes used in Grandma and Grandpa’s old tube radio receivers, TV’s and record players, etc., which you never see with standby switches, do you? Therefore, why would a guitar amplifier be different than these other devices? Because they are not! Fender’s first “Tweed” amplifiers also did not have a standby switch!

    For Leo Fender, tubes were cheap back then and actually made much stronger than tubes we have today, so why would he have this supposed concern for tube life? In order to get the tone he wanted, many of his designs are actually very hard on tubes pushing the limits of their power capabilities, therefore it stands to reason that tube life was not his concern.

    The standby switch on a Fender amp was put there by Leo to solve a problem he had later when building the much demanded larger power amplifiers using higher voltages to operate."
     
    EatS1stBassist and gebass6 like this.
  8. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Just take your beer on stage, no need for standby. ;)
     
    Zbysek, Pulverizor, fig and 12 others like this.
  9. Omega Monkey

    Omega Monkey

    Mar 8, 2015
    That's because people are easily swayed by myth and urban legend. These pieces of gear are designed for 1000s or 10s of 1000s of power cycles. It makes ZERO sense that leaving the thing on for years at a time would somehow be better than turning it off and on under normal usage. How often do you switch on and off the lights in your house? And how long do lightbulbs last? Obviously not exactly the same, but it should give you an idea of how long electrical devices can last under normal usage.

    Obviously, you probably shouldn't try to use the pilot light on your vintage tube amp as a strobe effect for a music video, but under normal usage, you will be fine.

    Also, at some point, you have to wonder anyway when constantly applied voltage and current become more of an issue than turning something on again after a break. Think of a car. Sure, everyone just looks at mileage, but you could have a car with 5000 miles on it, but if it's 80 years old and hasn't been maintained, a lot of parts just deteriorate with time, not only with usage. So the key is to try to get the wear and tear of time vs usage in the same general time frame. It's not good if you never use the thing, trying to preserve it, and then time takes it's toll anyway. Nor is it good if you use it to death and it dies prematurely.

    So I ask, all the purveyors of this pernicious myth, how many times of turning off and on again is it that destroys an amp (or other electrical device)? Is it 5? 10? 100? 1000? And at what number does it become completely ridiculous to triple your electrical bill to avoid a procedure your amp was designed to do approximately a zillion times?
     
    Aqualung60 and Wasnex like this.
  10. Omega Monkey

    Omega Monkey

    Mar 8, 2015
    Also, since you're local, can you tell me which studios those were so I can avoid them?
     
    Last edited: Jan 23, 2021
    Aqualung60 likes this.
  11. Omega Monkey

    Omega Monkey

    Mar 8, 2015
    I wonder if these people bring a UPS to gigs so they can keep their tube amp on in the car on the way home.
     
  12. Omega Monkey

    Omega Monkey

    Mar 8, 2015
    "Don't die on me now, baby! I know I only have 10000 power cycles with you, my love, but I don't want to have to use one up just because the band decided to play Rusty's Crab Shack on a tuesday night!"
     
    EatS1stBassist likes this.
  13. Wasnex

    Wasnex

    Dec 25, 2011
    IMHO the real answer probably varies from amp to amp. I use my standby when I turn the amp on and off. I also use it like a mute when I unplug an instrument or the speaker cable.

    If I am going to take a 20 minute break I put the amp in standby and leave the power on. If I am going to be take a much longer break I turn the amp off.

    Some people think the amp needs to be on for a significant time for it to sound it's best. If you believe this, you will probably leave the amp in operate mode during breaks, regardless of how long they are. The cost will most likely be shortened tube life.

    Whether using the standy or leaving the amp running all the time is hardest on the amp would depend on exactly what standby does and how the amp transitions from standby to operate. Some amps develop high bias in standby, so the output section is biased completely off when the amp is set to operate. This prevents the transient that some amps produce. It also means the amp needs a few seconds to for tube current to ramp up before the amp is ready to make good clean power.

    Other amps make a pretty significant thump when you set them to operate. This thump is voltage and current being applied quickly. My believe is this quick transition may represent more of a shock to the circuit and tubes. These amp are pretty much ready to play right away, but it will take about 20 minutes for the tubes to reach full operating temperature.

    Running the amp in standby only runs the heaters, so the cathodes are ready to emit electrons. The tubes will warm up, but not reach full operating temperature. Once the tube is passing electrons from the cathode to the plate, a lot more heat is generated in the tube.


    I think there is some concern with leaving a cathode biased amp running with no signal applied. If you plan to take a break either put the amp in standby or turn it off. The reason is because cathode biased amps actually run cooler when you are playing than when they are idling.

    Cathode biased amps are often called Class A, but few if any are actually class A. The Vox AC30 is the prime example. Max bias for one of these amps is up around 90% dissipation but some techs like to bias them over 100%. In other words, the tubes are constantly pulling more current at idle than they are designed to handle. I have read some posts that suggest certain techs like to bias AC30 designs at about 117%. Obviously these amps are very hard on the tubes, but the players who use them can pretty much afford to through in a new set every gig or so.

    I have read a couple of threads where it is said these amps cool down when they are cranked. Why? When you play music through the amp, the current level in the tubes goes up and down instead of staying at the constant 117% dissipation level. If you play the amp hard enough, the tubes have a chance to cool during the half cycle when they are at minimal current. Keep in mind the output section is push pull so one set off tubes will have increased current while the other set of tubes will have decreasing current. If run into clipping, the pull circuit may be completely cut off.

    Another factor that relates to this is when the amp is asked to make max power, the power supply voltages will sag. Less voltage=less current. Less current=less heat.

    There are some fairly scientific articles and possibly even a few studies on this if you hunt hard enough. From what I understand, the types of tubes used in guitar amps do not suffer significantly from cathode poisoning or cathode stripping, but I believe there is some minor effect. Essentially you don't want to leave the amp in standby for days at a time.

    As far as whether you should use the standby at all. Some amps do not have a standby. The two amps in my collection that do not have a standby are a JMI era Vox AC30 and a Matamp GT120. The Vox AC30 is cathode biased, so I don't think a standby is really much of a factor. The Matamp has fixed bias. The current ramps up smoothly when the tube cathodes get hot enough so I think it's fine.

    On a related note, we had a recent thread on an a vintage V4. If the amp was allowed to warm up in standby for a reasonable amount of time, it would work fine. If the standby was not used and the amp was simply set from off to "on, operate," the output tubes would red plate. Apparently it was taking longer for the bias supply to charge up than it was taking the B+ to charge up. So when the cathodes got hot enough to pass current, the tubes red plated.

    We suggested using the standby on this amp. The OP sent the tubes back and got a different brand. IMHO, although the current tube are not red plating, I think there is a good chance they are still being exposed to high current while the bias supply is ramping up, and that ultimately this will reduce tube life IMHO it would be best to let this amp run in standby for a short period of time so the bias supply can charge up fully. Here is the thread if you want to read it. NAD: Ampeg V4
     
    EatS1stBassist, Bent77, xn34 and 3 others like this.
  14. Omega Monkey

    Omega Monkey

    Mar 8, 2015
    *UPS beeps sadly and tragically as it loses charges, trying to keep those tubes charged up and ready to play Gimme Three Steps one more time...*
     
  15. Jim C

    Jim C I believe in the trilogy; Fender, Stingray, + G&L Supporting Member

    Nov 29, 2008
    Bethesda, MD
    I haven't had a beer in many years but this thread might send me there...
     
  16. Killing Floor

    Killing Floor Supporting Member

    Feb 7, 2020
    Austin, TX
    Not to derail the beer thread. But I use mine out of habit so I can leave active basses unplugged. I know I don’t have to do that for a short break but it’s a habit. Anyway, beer? You were saying?
     
  17. Wasnex

    Wasnex

    Dec 25, 2011

    IMHO It's not really worth worrying about all that much.

    I use the standby when I turn the amp on and off.
    -I let a short period of time pass when I turn the amp on, before I set the amp to operate. This ensures the bias supply has time to charge up.
    -I also let the amp sit in standby for a few seconds before turning the power off. This let's the tubes bleed the power supply down a bit before the bias supply is turned off. I have no proof but I think this is potentially safer and easier on the amp's components.
    I use the standby for short breaks and as a mute switch.
    -My intent as a mute switch is so I don't have to screw up my volume setting. None of my amps make a loud clack when I set them to operate. Some produce a thump. This is not a problem because the audio tech should be muting the sound system when we take a break.
    -Also if I am patching a different speaker, I don't like the idea of leaving the output section active when there is no load. This is probably overly paranoid, but the amp could potentially go into oscillation.
    -I have read some pretty well sourced articles that say cathode stripping and cathode poisoning is not a significant factor with common tubes used in guitar amps unless the tubes are exposed to bad conditions for days on end. So I don't think leaving an amp in standby for 20-30 minutes is a problem. However, it's your call if you want to leave the amp in operate, just consider what I wrote about cathode biased amps in post #13.

    The only time I have found when using the standby is problematic is when the tubes are going bad or tubes sockets are loose.

    I don't recommend leaving electronics running indefinitely. The common argument is it is less stressful on the circuit than turning it off an on. This does not consider a couple of things. 1. The transient from electric company switching puts a really nasty spike on the line that is much harder on the circuit than normal on/off operation. 2. If the device has active cooling, running it continuously will foul the internal structures with all sorts of nasty crap, so the device will need to be serviced. 3. If a circuit fails while no one is there to shut the circuit down, the damage is likely to be far more catastrophic--and the longer a piece is left running the greater the odds of a melt down.
     
    Last edited: Jan 23, 2021
  18. Wasnex

    Wasnex

    Dec 25, 2011
    Rezdog likes this.
  19. Jim C

    Jim C I believe in the trilogy; Fender, Stingray, + G&L Supporting Member

    Nov 29, 2008
    Bethesda, MD
    Wasnex: Agreed on all points other than leaving commercial electronics on 24/7. Back when I did that for a living, there were too many articles that supported less wear and tear on studio gear when left on.

    Thanks for the tech info to all and this is just a knee jerk reaction during small tube replacement.
    My SVT had a crackly pre amp tube.
    I was disgusted by all the mismatched and no name brand tubes and took the opportunity to roll some vintage Telefunken 12AX7's in the pre amp and NOS GE 12AU7 driver tubes. The amp was apart for a week and I really don't think there was much change in the overall tone which has always been excellent. It does produce more SPL at the same position on the master volume pot but that may be the only change.

    I think my only change in usage will be to turn the amp off if it won't be used for over an hour.
    Will continue to go to standby before power on / power off, and also between sets (assuming we get to do that again)
    @agedhorse
    @beans-on-toast
    Andy & David, any more thoughts on this?
     
    beans-on-toast likes this.
  20. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    If an amp has a standby switch I use it when power it up. The SVT is an example of where standby should be used when powering up. You want the power tube bias voltage to stabilize before the high voltage is applied. In this case, the design takes this into account. So with the SVT, use standby when powering up.

    When taking a break, I like to put the amp in standby. I don’t want to potential problems such as feedback starting when the rig is unattended.
     
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
    Mar 2, 2021

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