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Thread: Didn't blow up my amp today

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    Ultimate Tone Slacker Coma's Avatar
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    Default Didn't blow up my amp today

    Lugged my second 4x12 into my rehearsal space today and hooked it up. Amp is an EVH 5153, early serial. Forgot to switch the output selector over from 16 to 8. Played for 10 - 15 minutes or so before auddenly realising my mistake. Switch the amp off, set it to 8 ohm out, turned back on. Played for another hour. Output tranny seems fine - no smoke, no smell, no horrifyingly loud silence. Guess I dodged a potentially very expensive bullet.

    My only questions is... why? Conventional wisdom says you can connect a speaker load with higher impedance than the output and you'll be fine (I've tried it before - there's some tone suck but that's pretty much it) but shouldn't connect a lower load to the amp lest you'll send it to amp heaven.
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    Administrator Mincer's Avatar
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    Default Re: Didn't blow up my amp today

    I think it really depends on the design of the amp. Some amps don't tolerate mismatches well, and tubes will wear faster. Some do (my Mesa does) and you can use mismatches to change the tone. I never thought 10 minutes or so would kill an amp, though.
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    Toneologist kingswebe's Avatar
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    Default Re: Didn't blow up my amp today

    Quote Originally Posted by Mincer View Post
    ... I never thought 10 minutes or so would kill an amp, though.
    +1

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    Ultimate Tone Member JamesPaul's Avatar
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    Default Re: Didn't blow up my amp today

    Quote Originally Posted by Coma View Post
    Lugged my second 4x12 into my rehearsal space today and hooked it up. Amp is an EVH 5153, early serial. Forgot to switch the output selector over from 16 to 8. Played for 10 - 15 minutes or so before auddenly realising my mistake. Switch the amp off, set it to 8 ohm out, turned back on. Played for another hour. Output tranny seems fine - no smoke, no smell, no horrifyingly loud silence. Guess I dodged a potentially very expensive bullet.

    My only questions is... why? Conventional wisdom says you can connect a speaker load with higher impedance than the output and you'll be fine (I've tried it before - there's some tone suck but that's pretty much it) but shouldn't connect a lower load to the amp lest you'll send it to amp heaven.
    Review the Maximum Power Transfer Theorem. If the amp internal impedance and the load (speaker) impedance do not match, the amplifier dissipates the excess power not reaching the speaker.

    It is actually the inverse scenario of what you describe.

    When the speaker impedance is lower than what the amp is set for, it is the tubes dissipating the excess power. This is harder on your tubes.

    When the speaker impedance is higher than what the amp is set for, it is the transformer dissipating the excess power. This is harder on the transformer and the transformer runs a hotter.

    I avoid mismatching as I have never noticed any improvement in tone. Still many people and even some manufacturers will tell you a mismatch of one tap (16 ohm to 8 ohm, 8 ohm to 16 ohm, 8 ohm to 4 ohm or 4 ohm to 8 ohm) will not damage your amp. This has to do with impedance varying with frequency. Also manufacturers over-engineering the transformer size for a safety factor.

    What kills transformers is no speaker load. This is the case of speaker impedance being much higher than what the amp is set for. Actually an infinite ohm speaker. In this case all the power is dissipating in the transformer. This is why you never run a tube amp without a speaker load.
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    Ultimate Tone Slacker Jacew's Avatar
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    Default Re: Didn't blow up my amp today

    As a rule of thumb:

    You can safely use higher impedance speakers with SS amp no problem, but lose lot of power important for SS amps. Which is what I think was referred in original post.

    With tube amp you want to use lower impedance speakers for the reasons JamesPaul very well explained above.
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    LoveMachineologist jeremy's Avatar
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    Default Re: Didn't blow up my amp today

    yes and no, you dont want to go too low on a tube amp. an 8 ohm ot tap doesnt want to see a 2 ohm load on even a good amp for long. the power tubes will suffer since its the relationship between speaker and tubes the ot is dealing with. you are 100% correct on a ss amp, you dont want to go low since the amp may see it as a short and give up the smoke but higher is ok. youll just get less power. 99.9% of the time, its best to match things properly

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    Ultimate Tone Slacker Jacew's Avatar
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    Default Re: Didn't blow up my amp today

    Quote Originally Posted by jeremy View Post
    yes and no, you dont want to go too low on a tube amp. an 8 ohm ot tap doesnt want to see a 2 ohm load on even a good amp for long. the power tubes will suffer since its the relationship between speaker and tubes the ot is dealing with. you are 100% correct on a ss amp, you dont want to go low since the amp may see it as a short and give up the smoke but higher is ok. youll just get less power. 99.9% of the time, its best to match things properly
    I thought that obvious from earlier posts in this thread, but good to point out.

    You should always use matching impedance in tube amps in general, but it's safer to go lower than higher if you can't.
    Last edited by Jacew; 01-08-2020 at 10:01 PM.
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    Mojo's Minions devastone's Avatar
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    Default Re: Didn't blow up my amp today

    People on the interwebs get very worked up about this stuff (duh), but honestly, having the selector switch on the wrong setting won't really hurt most good quality tube amps. It may put a little more wear on the tubes depending on which way the setting goes, but transformers, again, good quality, should be overdesigned enough that it doesn't bother them. Can't speak to some of the MIC amps where they have cut every corner possible, but I would still bet the transformer is stout enough to be fine.

    Some of the Fenders heads, the Tone Master (?), had settings of high, medium, and low on the selector and you were encouraged to experiment to find the one that sounded right for you.

    That said, don't run them below 4 ohms or above 16, and yes it is best to keep things matched. But having the switch set wrong is nothing to freak out about. Running without a cab, yeah, that's bad, but still, if it takes you few minutes to figure out why you don't have any sound coming out, probably not going to smoke it, any good designer would have realized that stuff like this will happen and design it well enough to prevent "reasonable" catastrophic failure. The industry term is FMEA, Failure Modes and Effects Analysis, which is done on most products, or at least should be. If you are in the medical field, it is required and reviewed by the FDA, in aerospace, if people are involved it is highly reviewed, if it's a satellite, failure to find potential failures can cost hundreds of 100s if not millions of $. But as recent news has shown, stuff can slip through the cracks of the biggest and best companies (Boeing).

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    Mojo's Minions
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    Default Re: Didn't blow up my amp today

    My buddy from the UK who has passed now did a whole US tour with his Marshall JCM800 2203 set accidentally to 16 on a 8 ohm cab.

    On one of the very last shows of the tour, I noticed it when I shared his rig in Asheville NC

    Didn't hurt anything after 40 shows -just changed the tone slightly.
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  10. #10
    Mojo's Minions devastone's Avatar
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    Default Re: Didn't blow up my amp today

    From the Tone Master Manual, again, not saying this is true for all amps:

    D. IMPEDANCE SWITCH - This is labeled LO, MED and HI. This switch serves two functions.
    One, to set the output impedance of the amplifier to best match the speaker impedance for
    maximum power. Second, to enable the amplifier to better achieve the cranked-up sound at a lower
    volume. On the B CHANNEL, with a single Tone-Master enclosure, this switch should be set
    according to the setting of the B CHANNEL volume knob: For volume settings of 3.5 and lower,
    LO would be the appropriate setting. For settings of 3.5 to 7, MED is best. For settings above 7,
    HI will produce full power and tone. This switch will not damage tubes or reduce tube life at
    these settings. What it does do is increase the gain in the LO and MED settings and thereby better approximate the Full volume sound at a lower level than by adjusting the VOLUME alone.
    With a single 16Ω enclosure, LO will produce 30 watts, MED will Produce 60 watts, and HI will
    produce a full 100 watts. With two 16Ω enclosures, (an 8Ω load), LO will produce 60 watts, and
    MED will Produce 100 watts. In the A CHANNEL, the switch has the same function, although
    blues players may like running the switch on LO all the time to get that great crying tone.
    Conversely, a player looking for a New Wave Strat® tone might like the sound of the A CHANNEL
    on HI.

  11. #11
    LoveMachineologist jeremy's Avatar
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    Default Re: Didn't blow up my amp today

    that was such a cool amp!

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    of the Forum PFDarkside's Avatar
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    Default Re: Didn't blow up my amp today

    Refreshing to see a couple of people understand that tube amps and solid state amps operate differently, and that speakers impedance and amp output impedance mismatch is different for tube amps and solid state.
    Last edited by PFDarkside; 01-11-2020 at 07:38 AM.
    Oh no.....


    Oh Yeah!

  13. #13
    Ultimate Tone Slacker Jacew's Avatar
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    Default Re: Didn't blow up my amp today

    Quote Originally Posted by devastone View Post
    People on the interwebs get very worked up about this stuff (duh), but honestly, having the selector switch on the wrong setting won't really hurt most good quality tube amps. It may put a little more wear on the tubes depending on which way the setting goes, but transformers, again, good quality, should be overdesigned enough that it doesn't bother them. Can't speak to some of the MIC amps where they have cut every corner possible, but I would still bet the transformer is stout enough to be fine.

    Some of the Fenders heads, the Tone Master (?), had settings of high, medium, and low on the selector and you were encouraged to experiment to find the one that sounded right for you.

    That said, don't run them below 4 ohms or above 16, and yes it is best to keep things matched. But having the switch set wrong is nothing to freak out about. Running without a cab, yeah, that's bad, but still, if it takes you few minutes to figure out why you don't have any sound coming out, probably not going to smoke it, any good designer would have realized that stuff like this will happen and design it well enough to prevent "reasonable" catastrophic failure. The industry term is FMEA, Failure Modes and Effects Analysis, which is done on most products, or at least should be. If you are in the medical field, it is required and reviewed by the FDA, in aerospace, if people are involved it is highly reviewed, if it's a satellite, failure to find potential failures can cost hundreds of 100s if not millions of $. But as recent news has shown, stuff can slip through the cracks of the biggest and best companies (Boeing).
    I once forgot to connect Orange TT to speaker. Burning smell coming out of it almost right away made me realize that mistake very quickly.

    Didn't break anything though.
    "So understand/Don't waste your time always searching for those wasted years/Face up, make your stand/And realize you're living in the golden years"
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  14. #14
    Mojo's Minions devastone's Avatar
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    Default Re: Didn't blow up my amp today

    Quote Originally Posted by Jacew View Post
    I once forgot to connect Orange TT to speaker. Burning smell coming out of it almost right away made me realize that mistake very quickly.

    Didn't break anything though.
    Yeah, that's why I'm trying to be careful to say "probably", "most of the time", "most amps" (meaning not all). I've done that with old Marshalls and took me a few to figure out why there wasn't any sound, but yeah, they don't build them like they used to, or maybe I just got really lucky.

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    Toneologist JMP/HBE's Avatar
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    Default Re: Didn't blow up my amp today


  16. #16
    OH THE GLAZE! Clint 55's Avatar
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    Default Re: Didn't blow up my amp today

    ^ Ya and there's no feedback.
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    OH THE GLAZE! Clint 55's Avatar
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    Default Re: Didn't blow up my amp today

    So if you play your amp without the speaker plugged in, it will blow up?
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  18. #18
    Toneologist JMP/HBE's Avatar
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    Default Re: Didn't blow up my amp today

    Quote Originally Posted by Clint 55 View Post
    So if you play your amp without the speaker plugged in, it will blow up?


    You can fry your output transformer playing a tube amp with no load.
    You can also fry your output transformer using a mismatched load.

    If you're lucky sometimes you can get away with small mistakes.

    If you have a tube problem or a tube crap out lots of times it takes out other components as well leading to costly repairs.

    For best results always match impedance & have regular maintenance to Thermionic Valve Amplifiers.
    Last edited by JMP/HBE; 01-14-2020 at 07:32 PM.

  19. #19
    Administrator Mincer's Avatar
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    Default Re: Didn't blow up my amp today

    Some amps can handle a mismatch better than others. My Mesa has this as a 'feature' for a different tone as long as you don't go too high or low. Read the manual before you attempt this, and if you still don't know, consult the manufacturer.
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    Mojo's Minions devastone's Avatar
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    Default Re: Didn't blow up my amp today

    Quote Originally Posted by Clint 55 View Post
    So if you play your amp without the speaker plugged in, it will blow up?
    Solid State, no, tube amp, yes.

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