Turning on head accidentally without speaker attached question

Saberslash

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First of all, sorry if there is already similar topic in the forum :)

My question is, today I accidentally turned on my Marshall Silver Jubilee head for approximately 2 minutes (maybe less) without speaker attached to head. As soon as I noticed I shut it off, afterwards I reconnected everything and amp plays as before.

Situation was like this: Head turned on standby, no speaker attached to head, all pots on 0, no guitar attached. Could that possibly do any damage?

I ve heard people burn their amps while speaker is not connected when they try to play guitar and they crank volume up a bit.
Also I ve read that if amp is is standby and no guitar is connected, it could be turned on like that 100 years and amp won't get damaged..

Also I found this online, is this true statement?

"Most tube amps have shorting type speaker jacks to prevent flyback voltage in case you forget to plug in a speaker. But, if you plug a cable into the amp and not plug the other end of the cable into a speaker, then you have an open circuit that can cause flyback if the amp is played loud enough to generate the flyback. But what's "loud enough" to cause flyback damage? Amps aren't created equal so it would be difficult to say. However, there's a misconception that just turning a tube amp on with no load will damage it. With no input signal, flyback can't be generated...so an amp with no load and no input signal will sit there and do nothing for 100 years if the tubes last that long. It's only when there's enough signal from the amp (or it's in self oscillation) that flyback can be generated with no load. But, again, most tube amps have shorting speaker jacks that prevent flyback from occurring even with signal into the amp and the volume turned up."

Thank you all in advance, appreciate your answers, especially if they are explained from technical and electrical perspective since I am interested to know more.
 

Saberslash

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I do not sweat it, I just wonder if there is any technical explanation on this :D
And does amp on stanby and no signal form guitar plays any role here :)
 

nix_gibby

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I did this a few times with my SJ head, even played a few chords, and when I realized there was no sound I turned the amp off, attached the speakers, turned it back on, and everything was fine.
In your case, absolutely nothing could happen.
It's important there is no any loud signal going through the amp, because there is no load and OT could burn out, but even in that case you should play the amp "loud" for a few minutes to melt down the OT.
 

Saberslash

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I did this a few times with my SJ head, even played a few chords, and when I realized there was no sound I turned the amp off, attached the speakers, turned it back on, and everything was fine.
In your case, absolutely nothing could happen.
It's important there is no any loud signal going through the amp, because there is no load and OT could burn out, but even in that case you should play the amp "loud" for a few minutes to melt down the OT.

Is OT working when amp is in standby?
 

chromeboy

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I used to used 3 heads and cabs. One head through two cabs, 1 as a back up and one head and cab for friends who would sit in front n gigs. My standby head was always powered up with no speakers plugged in but it was on standby. If my main head would go down then my roadie would just unplug the cabs from the down cab and plug them in my backup. Only needed to do that once but as was said as long as the amp is in standby you'll be safe.
 

alpha al

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Also I found this online, is this true statement?

"Most tube amps have shorting type speaker jacks to prevent flyback voltage in case you forget to plug in a speaker. But, if you plug a cable into the amp and not plug the other end of the cable into a speaker, then you have an open circuit that can cause flyback if the amp is played loud enough to generate the flyback. But what's "loud enough" to cause flyback damage? Amps aren't created equal so it would be difficult to say. However, there's a misconception that just turning a tube amp on with no load will damage it. With no input signal, flyback can't be generated...so an amp with no load and no input signal will sit there and do nothing for 100 years if the tubes last that long. It's only when there's enough signal from the amp (or it's in self oscillation) that flyback can be generated with no load. But, again, most tube amps have shorting speaker jacks that prevent flyback from occurring even with signal into the amp and the volume turned up."
Marshalls do NOT have shorting jacks for the outputs. I always thought they should, but they don't. It would save a lot of output transformers. Most Fenders do have those. If you have shorting jacks, you must use the main output jack first, the extension speaker jack will not work unless the main speaker jack is in use.
 

Saberslash

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Marshalls do NOT have shorting jacks for the outputs. I always thought they should, but they don't. It would save a lot of output transformers. Most Fenders do have those. If you have shorting jacks, you must use the main output jack first, the extension speaker jack will not work unless the main speaker jack is in use.
Thanks for the info. But again, since amplifier was in standby nothing could possibly happen?
This is what Marshall customer service responded to me:

“The damage caused without a speaker connected is to the mains transformer so the output transformer will be fine, if damage had been caused you would experience low volume and distortion.”
 

Mitchell Pearrow

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Thanks for the info. But again, since amplifier was in standby nothing could possibly happen?
This is what Marshall customer service responded to me:

“The damage caused without a speaker connected is to the mains transformer so the output transformer will be fine, if damage had been caused you would experience low volume and distortion.”
You are fine my friend
Just as said above (don’t do it again)
Cheers
Mitch
 

PelliX

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Thanks for the info. But again, since amplifier was in standby nothing could possibly happen?

Correct. In a nutshell, if the amp is on standby, you can connect a guitar, play it, fiddle the knobs, no worries. If there's no load AND it's NOT on standby, you must not let any signal pass through it (or as little as possible). It's about the amount of energy being dissipated by the output stage.

This is what Marshall customer service responded to me:

“The damage caused without a speaker connected is to the mains transformer so the output transformer will be fine, if damage had been caused you would experience low volume and distortion.”

:facepalm: Yeah, that's Marshall CS for you. I mean... the mains transformer... fuses... just ignore them.

TL;DR: Just don't make it a habit. ;)
 

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