Adding standby switch?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by rockon1, Sep 5, 2006.

  1. rockon1

    rockon1 Member

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    Ive got an amp (OK,dont laugh,its an old Crate Stealth GT50 and I really like it)but there is no stand by switch. How difficult would it be to wire one in it? Often I turn my amps on and come back to them throughout the day. Without a standby switch it doesnt seem like a good idea. Thanks Bob
     
  2. tonezoneonline

    tonezoneonline Member

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    Your amp does not need a standby switch.Even with one the purpose of the standby switch is not to leave your amp on standby for extended periods of ttime.
     
  3. CjRuckus

    CjRuckus Member

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  4. rockon1

    rockon1 Member

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    Hmmm. Ive always thought it was better to turn it on and off standby,say,5 times in a few hours than to powerup the tubes 5 tmes directly without warm up,or leave them powered up. Thats got to reduce their life?:worried
     
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  5. bob-i

    bob-i Member

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    At the voltages guitar amps run, standby is not really necessary. It's more of a convienance than protection for the amp.
     
  6. rockon1

    rockon1 Member

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    So letting run at idle wont wear out the tubes any faster than on standby?
     
  7. bob-i

    bob-i Member

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    Shut the amp off. :nono Why run it when you're not playing?
     
  8. rockon1

    rockon1 Member

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    Well I have a habit of going back and forth from my guitar sometimes and I usually just put my other amps on standby.I thought that was OK. I guess I was wrong?:confused:
     
  9. danieldroukas

    danieldroukas Member

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    Standby is only NEEDED on tube amplifiers that have a solid state rectifier. This is because the filaments of the vacuum tubes need to heat up the surrounding components so the tube can function properly. When you turn the amp on without letting the tubes warm up first you get what's called cathode stripping, and this greatly decreases the longevity and tone of your tubes.

    Amps that have a vacuum tube for the rectifier don't necessarily need a standby switch because the rectifier doesn't apply the full B+ until it itself has warmed up. Amps with a solid state rectifier DO need a standby switch because the diodes instantly apply the full B+. Think of your old Fender Champ with a 5Y3 rectifier and just a power on/off switch.

    If I were you, I certainly wouldn't leave the amp on standby for hours on end. If you're going to use it then turn it on, wait ~2 minutes, plug in and play. If you're going to walk away for only a few minutes then standby is fine. If you're going to leave to buy groceries... turn it off.
     
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  10. bob-i

    bob-i Member

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    I personally never leave an amp on, call me cheep but I try to save electricity. Since it still takes a minute or so for the tubes to stabilize anyway you might as well shut them off.

    There's no right or wrong here. If you want to leave your amps on standby, go for it, it won't hurt anything. I actually build amps without standby switches at times if there's no room for it. No harm in that either.
     
  11. donnyjaguar

    donnyjaguar Member

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    Actually, I don't think this is conjecture. If you leave a filament on for a short while I'm certain its less stressful than shutting it off and then back on again repeatedly.

    Think of it this way. How often does an incandescent lightbulb (in your house or even the headlamps on your car) blow when its already on? How often does it blow when you first turn it on? In my experience its the latter. I can't even remember a bulb ever blowing when it was already on - this seems to happen only in teenage slasher films. :)
     
  12. donnyjaguar

    donnyjaguar Member

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    Agreed with OTM. What I've found with vacuum tube rectifiers is that they start passing current long before the balance of the tubes in the circuit are warmed up and ready. I've also found that the indirectly heated type, such as the GZ34, are ready to go before 6CA7 tubes. What can you do? I guess just put in a standby switch even if its a vacuum tube rectifier.
     
  13. brad347

    brad347 Member

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    applying voltages to cold tubes can result in cathode stripping. This definitely shortens tube life. It is my understanding that leaving an amp on standby for extended periods doesn't cause appreciable wear, but leaving it on with high voltage to the plates will cause wear somewhat. In any case, I think of it sort of like your car.

    Most of the wear on the engine of your car comes when you first start it. This is because the oil is down in the crankcase and it takes a minute for the oil to circulate and do its protecting-lubricating business. For this reason, it causes more wear to the engine to turn it on and off repeatedly than just to let it run. In the case of tubes, once they are warmed up, then they can run for awhile and it's less stressful to the cathodes than starting them up cold. A standby allows you to have your cake and eat it too.
     
  14. rockon1

    rockon1 Member

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    So in a case,like I often do, where your playing for 15 or 20 minutes say 5 times in a few hours a stand by switch causes less wear than turning the amp off and on without a stand by switch 5 times in the same amount of time?
     
  15. John Phillips

    John Phillips Member

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    I would say so, yes. It also causes less tube wear than simply leaving it on fully. I usually put the amp on standby, not off, if I'm going to be playing again within an hour or two.

    There are three issues:

    1. If you turn if off and back on, you add heating/cooling cycles which can cause tubes to fail, and also possibly other components and solder joints in the amp. You also cause cathode stripping at start-up each time if you don't have a standby switch.

    2. If you simply leave it on fully, you're slowly wearing the tubes out since current is flowing.

    3. If you put it on standby - with the filaments on but no current flowing - you're causing a problem known as 'cathode poisoning', where the cathode coating becomes less effective. This definitely occurs, but how serious it is I don't know, or whether it reverses itself (or if so, how quickly) once the current starts to flow again - I've never been able to find a definitive answer. It doesn't seem to make any noticeable difference in my own experience.

    So given two good reasons to use one and one questionable reason not to, I use the standby switch rather than turn the amp off, unless I'm going to be putting the amp away for the day.

    Yes, you are wasting energy... assuming it's not winter and you need to keep your house warm :). But if you burn your tubes out you're wasting energy (in their manufacture) and materials too, so there really is no perfect answer other than not to turn it on at all. (And if you use old-stock tubes, these are a finite resource so IMO are the more important factor.)


    donny is right about tube filaments normally only burning out at start-up BTW - in the days of tube computers with thousands of tubes, any one of which could stop the whole thing working properly if it went out, the best reliability was found to be achieved by never turning them off. (They didn't use power tubes though, so tube wear was less of a factor than outright failure.)
     
  16. rockon1

    rockon1 Member

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    SOOOOOOooooooooooo....how hard is it to install a standby switch? I think I could accomplish it if pointed in the right direction.
     
  17. John Phillips

    John Phillips Member

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    On a tube rectified amp it should be after the first filter cap - but before the supply to the OT and other caps - because otherwise the heavy initial current draw when you flip the switch on, with an empty cap on the other side of it, will severely stress the rectifier tube and may damage it.

    On SS-rectified amps, it's usual to put it before all the filter caps, because the SS diodes normally used in rectifiers have such a high current rating that the initial draw doesn't matter.


    rockon - I'm assuming from the amp brand and model that it's going to be a solid-state-rectified, PCB-built amp. This makes things harder since the connection from the diodes to the filter caps is probably a board trace. Rather than modify the board, the best way to do it IMO would be to use a double-pole switch between the PT secondary connections and the board. Marshall and many others do it this way. (Or, if the rectifier is just two diodes with a center-tapped PT secondary, you just need a single-pole switch in the center-to-ground connection.)

    If you're lucky, the wires from the PT to the board will be long enough to reach to the place you've chosen for the switch, so you just need to add new wires from the switch back to the board and you're done. Make sure you use adequately-rated wire (600V 1A minimum).
     
  18. rockon1

    rockon1 Member

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    Thanks guys,these are the answers Ive been looking for.

    John Phillips- Yes its an old "bottom feeder" Crate Stealth but I love the sound the amp puts out! Its an odd 6V6 based amp-at least for an amp geared towards metal! At any rate sounds simple enough to wire in a switch where you suggested. Need to have a look inside. Thanks Bob
     

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