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Risk scenario: tube amp and power outage?

Discussion in 'Amps and Cabs [BG]' started by KF2B, Jan 13, 2017.

  1. KF2B


    Jan 28, 2013
    Yeah, that´s what happened :dead:

    And precisely after I had installed nos pre tubes (2 x 12AT7WA) and power tubes (2 x KT88) less than a week ago.

    So what is happening when that - power outage while playing a tube amp - happens? I guess it pretty is the same as cutting the power off straight without setting on standby first. And that made me think: while I know that is a no-no with a tube amp, I actually do not know why not beyond the fact that it might shorten the tubes lifespan? - As you can fathom I am totally clueless with amps what comes to the actual workings of them.

    So here goes:
    1. what is the risk scenario with power outage while playing a tube amp?
    2. will the power outage / powering off (without standby first) do something to the tubes?
    3. how much will the tube´s life-expectancy shorten when the above takes places
    Sorry for the rookie questions but I really do not know, and I did not find the answer with search. So... I´d appreciate if you could give of your experience.

    Oh... What is evident now is that the amp makes noticeably more background hum now when the standby is off (playing) than it used to before. The background noise with the standby engaged is pretty much the same as it was before.

    F**k!... :banghead:

    Last edited: Jan 13, 2017
  2. Not a no no at all. Tubes barely cool at all on standby with the heaters going.
  3. I have yet to have an amp fail me, tube or SS, after a power outage. Many years ago I played a club where the owner had fed the stage power through a Variac so that if the band gets a bit loud he could turn them down a bit. That abuse didn’t harm my stuff either.
    spankdaplank and MobileHolmes like this.
  4. RoadRanger

    RoadRanger Supporting Member

    Feb 18, 2004
    NE CT
    You've been reading TB again, eh ;) ? That BS. I'll warm up a tube amp on standby 15 seconds or so (not really necessary on most) but just use the "off" switch when done. Standby is for muting the amp and for between sets.
    Coolhandjjl likes this.
  5. To put this in perspective many many amps were built that did not even have a standby switch. They are a convenience at best and certainly not a necessity!
    lfmn16 and MobileHolmes like this.
  6. Rick James

    Rick James Banned

    Feb 24, 2007
    New Jersey
    The only reason for a standby switch is so you can go on break, come back on stage and not have to warm up the tube heaters again before the amp will work.
    Some guy invented a way to learn about things that you don't understand. They call it 'a book'. :cool:
    lfmn16 likes this.
  7. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Not true. By turning off the tube's quiscent conduction (set by the grid bias), you eliminate the quiscent plate dissipation and are left only with heater power.
    fdeck likes this.
  8. ThisBass


    Aug 29, 2012
    Pentodes can get very very hot when pusehed hard.
    Personally I use "standby" to let the tubes slowly cool down for around 10 minutes and then switch off main-power (which is actually the heating).
    Last edited: Jan 13, 2017
  9. Going back a long time to my school daze I remember that having the heaters on with no B+ leads to "cathode stripping”. I’ve never let that bother me and I’ve always had excellent tube life.
  10. So what's the net difference between going to standby for a few minutes instead of turning off?
  11. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Slower cooling down of the internal structures, lowering mechanical stresses.
  12. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    I think that it depends on how the power fails.

    For instance, it there was a surge or a brownout prior to the power failing, it could have adversely affected the amp. Depending on the amp, fuses may have mitigated any damage.
  13. DrummerwStrings


    Mar 27, 2015
    I thought the main purpose of a standby switch was to warm up the tubes before they are put to work, and a well-designed amp with tube rectification doesn't need a standby switch because by the time the rectifier tube warms up & starts converting AC power to DC in the circuit, the tubes are ready. Sounds like they help with shutdown, too.

    I enjoyed (re)reading Dave Hunter's "The Guitar Amp Handbook", but you may start looking for old amps to tinker with:

    The Guitar Amp Handbook: Understanding Tube Amplifiers and Getting Great Sounds (Updated and Expanded Edition): Dave Hunter: 9781480392885: Amazon.com: Books

    You can give your electronic equipment some protection with either of these:

    Furman M-8x2

    APC BN700MC Back-UPS 700 VA 8-Outlet Uninterruptible Power Supply (UPS)-Newegg.com
  14. KF2B


    Jan 28, 2013
    Thank you for sharing of your knowledge!
  15. lfmn16

    lfmn16 Supporting Member

    Sep 21, 2011
    charles town, wv
    But getting the knowledge out of said 'book' requires something called 'effort,' a concept which seems to be lost on one or more generations.
  16. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Standby is an interesting topic.

    A standby switch is not necessary for a tube amp to work. In the past many amps didn't have one, nor did radios and TV sets. Standy was popular in some communications equipment and migrated as a feature to musical instrument and some hi-fi amps.

    In order for the tube to work, the heater needs to heat the cathode to cause electrons to boil off and float inside the bottle. The tube works and amplifies by controlling the flow of these electrons. When the amp is in standby, just the heater is on, it serves to bring the cathode up to operating temperature.

    There are two main types of rectifier tubes. Those with directly heated cathodes and and those with indirectly heated cathodes. The 5AR4, which is commonly found in amps is indirectly heated and turns on slower. Another common rectifier in smaller amps is the 5Y3. It has a directly heated cathode and begins working much quicker. It doesn't provide the slow turnon that the 5AR4 does. So it depends on the amp. There are other ways to provide a delayed turnon and these are employed in some amps.

    When turning off an amp, you do not need to put it into standby first. Simply turn off the power. An exception is if the amp has a fan that stays on when the amp is in standby. This can help cool down the amp before turning off the power. This can help avoid thermal shock, especially where it is cold outside.
    DrummerwStrings likes this.
  17. levis76

    levis76 Seconds from getting ba... Supporting Member

    Apr 14, 2007
    Metro Detroit
    I always d/l and read the manuals for my gear and I power up and down in whatever manner the manufacturer specified. Never rely on general consensus knowledge, as stated earlier different manufacturers use different designs that require different operating procedures. Put simply, there is no universal right way to power up/down an amp.
  18. seamonkey


    Aug 6, 2004
    Most likely just your imagination
  19. john m

    john m Supporting Member

    Jan 15, 2006
    Had a Sunn T in the late 70,s , early 80's. Did 100+ gigs/year.
    When the last set was over, both switches were turned off and the break down and load out began.
    Tube amps went out 2nd to last in the cold New England winters.
    Instruments were always last.
    My tubes got replaced once due to the amp getting knocked over-- same with my Bassman 50 in 1972
    spankdaplank likes this.
  20. KF2B


    Jan 28, 2013

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