close call with single rectifier: impedence mismatching (long read)

[muttonchopsrule]

so now that i have my dual rectifier, i'm letting my other guitarist borrow my single recto until it becomes his tomorrow when i get his money.

he was setting it up through another buddy's cabinet, which had the exact same back plate as my marshall cab (the 4 or 16 ohm mono inputs, or the 8 ohm stereo). the cab was set for mono, and was coming out of the 4 ohm output from the amp. unfortunately, he wasn't careful enough to double check that he plugged into the right input on the cab. by accident, he had plugged into the 16 ohm input.

so we have an amp running at 4 ohms, plugged into a cab set at 16.

about ten minutes into our practice, the amp completely shuts off. i thought at first that it may have come unplugged from the wall. i check that, everything appears to be fine. the amp won't fire up, so i checked the fuse. the fuse had blown, so i put another one in there and as soon as i fire it up and turn the stand-by off, there was a loud humm coming out of the speakers, followed by the amp shutting off again. when i looked over everything, i discovered that the impedence was indeed mismatched, which was definitely the cause of all this nonsense.

at this point, i became extremely angry because i immediately thought the output transformer was toast. but i was relieved to find that it was just the power tubes, which had completely fried. fortunately i had a pair of 6L6's lying around that i had from before i put the EL34's in there. so several fuses and a pair of tubes later, the amp fired up and everything sounded alright.

moral of the story: ALWAYS ALWAYS ALWAYS make sure your impedence is matched correctly when using a high quality tube amp. and especailly if you're in a band that plays out frequently, ALWAYS have spare fuses and tubes.

and god d***it, that was a perfectly good pair of EL34's....

 

[Guitarist]

Re: close call with single rectifier: impedence mismatching (long read)

I'm sorry that happened!

Nice work being prepared and using your noggin'. Some idiot probably would've ripped all the cords from the amp and sent it to their tech.

 

[Xeromus]

Re: close call with single rectifier: impedence mismatching (long read)

I repeat, NEVER let friends borrow guitar gear.

 

[SOLO GUITAR STEWIE]

Re: close call with single rectifier: impedence mismatching (long read)

Good thing you had spares and where able to figure the problem out. And better to
replace tubes and fuses than the entire friggin amp.

chris

 

[Jeff Seal]

Re: close call with single rectifier: impedence mismatching (long read)

Impedance mismatches are rarely "detrimental", and quite honestly, this topic has been blown way out of proportion!.....(just a general observation based on the general understanding of this on the web, no offense meant to muttonchopsrule..)
I repair amps all day long, and have only seen two transformers burnt due to impedance issues in 18 yrs!..(same guy running 4 412's each wired at 4 ohms!)
I'm only trying to dispell some of the "myths" that are rather "rampant" these days....

If you don't believe me........

http://www.mesaboogie.com/manuals/2chRecto.pdf

Mesa's are well known for pushing tubes really hard, and tube failure is about as common as getting a flat tire...nothing against Mesa....or any tire company for that matter.... it's just the way it is!

keep on rockin'

Jeff Seal

 

[Zerberus]

Re: close call with single rectifier: impedence mismatching (long read)

...
so we have an amp running at 4 ohms, plugged into a cab set at 16.

This is a non-issue on a Mesa amplifier, thje Rectifier manual even specifically lists this mismatch as a possible hookup scheme. And mismatching a tube amp UPWARDS will almost never cause problems, regardless of amp....

I run my Mesa Stereo 50:50 into 2 16 ohm cabs and it only has 8 ohm outputs, the only difference is a tonal one, the amp "squishes" more ....

about ten minutes into our practice, the amp completely shuts off. i thought at first that it may have come unplugged from the wall. i check that, everything appears to be fine. the amp won't fire up, so i checked the fuse. the fuse had blown, so i put another one in there and as soon as i fire it up and turn the stand-by off, there was a loud humm coming out of the speakers, followed by the amp shutting off again. when i looked over everything, i discovered that the impedence was indeed mismatched, which was definitely the cause of all this nonsense.

This is almost 100% certain not a speaker or output tranny issue but a blown power tube.... Mismatches DO put some extra stress on the tubes, and 16/4 is a pretty hefty one, it´s understandable wh the tubes would fail....

moral of the story: ALWAYS ALWAYS ALWAYS make sure your impedence is matched correctly when using a high quality tube amp. ...

Moral of my post (and no disrespect is meant by this, so sorry if it comes off that way, I seem to be a bit wierd this morning): RTFM first

and especailly if you're in a band that plays out frequently, ALWAYS have spare fuses and tubes.
.....
and god d***it, that was a perfectly good pair of EL34's....

I recommend velcroing a box of fuses and a few ettra tubes to the inside of the head or back of the rack for this exact reason

 

[The Golden Boy]

Re: close call with single rectifier: impedence mismatching (long read)

I recommend velcroing a box of fuses and a few ettra tubes to the inside of the head or back of the rack for this exact reason

My bass head overheats and blows output fuses, I have a few packages of fuses taped to the back wall of the rack, a few for each channel and a bunch for the output fuses.

The overheating issue was circumvented by installing a fan on the top rack rail.

I don't care what anyone says, putting a fan in the center of the amp to passively draw air in the back and blow air out a vent the size of a nickel in the SIDE of the amp- that's bad engineering.

My main guitar amp is a 78 Marshall- the kind with the removable impedance selector. If that happens to fall out on the way to a show, you're pretty well sunk. I keep a wire with soldered ends duck taped to the back of the amp with a diagram of what position is what impedance.

 

[mnbaseball91]

Re: close call with single rectifier: impedence mismatching (long read)

You think that's bad? I went into GC a few months ago to buy a case for my guitar. It was pretty empty so I decided to check out a few amps. The guy hands me a cable and says "just plug into whatever you want, everything should be hooked up." OK, so I noodle around on a Blues Junior for a while before the inevitable happens: I graduate over to where they have a 70's Plexi set up on top of two 1960 cabs. I turn it on, but can't get any sound of it. So I'm standing there waiting for the tubes to warm up a little longer, and the guy comes running over shouting at me to turn it off. Turns out they had the power cable plugged in but no cab hooked up! Now who's bright idea was that!? Anyway, the fuse wasn't blown, but the amp didn't work. Then I left.

 

[NecroPolo]

Re: close call with single rectifier: impedence mismatching (long read)

For over 8 years, I used a '60s Selmer Treble & Bass amp with a 4-ohms cab (that I believed to be 8 ohms) with the Selmer's 7.5 ohms output - and never, ever had a problem. Okay it is prolly up to design and the Selm doesn't run the EL34 tubes at full power.

 

[muttonchopsrule]

Re: close call with single rectifier: impedence mismatching (long read)

This is a non-issue on a Mesa amplifier, thje Rectifier manual even specifically lists this mismatch as a possible hookup scheme. And mismatching a tube amp UPWARDS will almost never cause problems, regardless of amp....

well, seeing as what happened, apparently it is

Moral of my post (and no disrespect is meant by this, so sorry if it comes off that way, I seem to be a bit wierd this morning): RTFM first

i've read the manual, thanks. and as you could see by reading the post, it was a careless mistake made my buddy who was playing through it at the time. granted i should have been more responsible and double checked that everything was connected properly. but regardless of what the manual says, a 16 ohm load connected to the 4 ohm tap obviously causes problems.

 

[Zerberus]

Re: close call with single rectifier: impedence mismatching (long read)

well, seeing as what happened, apparently it is

i've read the manual, thanks. and as you could see by reading the post, it was a careless mistake made my buddy who was playing through it at the time. granted i should have been more responsible and double checked that everything was connected properly. but regardless of what the manual says, a 16 ohm load connected to the 4 ohm tap obviously causes problems.

I´m still convinced that the mismatch itself wasn´t the cause... THere may be other problems that thhe mismatch compounded, or they may have been running a bit hot anyway (as Jeff said very common for a mesa)...

If anything the mismatch would destroy the TRANSFORMER if it were severely dangerous.... but since the whole amp didn´t go up in smoke I think we can rule that out....

and in over 10 years of using Mesa amps I´ve used all sorts of loads, including ones NOT recommended..... And I´ve never had problems.....

If it were my amp, the very first thing I´d do is hook it right back up to 4 ohms, and if the fuse blows again it´s on it´s way to a tech... Does not function as specified: either misengineered or defective, the tech can tell you which.. and if it´s misengineered, then it´s out the door before it can close it coming in

I still say it was the tubes

 

[muttonchopsrule]

Re: close call with single rectifier: impedence mismatching (long read)

I´m still convinced that the mismatch itself wasn´t the cause... THere may be other problems that thhe mismatch compounded, or they may have been running a bit hot anyway (as Jeff said very common for a mesa)...

If anything the mismatch would destroy the TRANSFORMER if it were severely dangerous.... but since the whole amp didn´t go up in smoke I think we can rule that out....

and in over 10 years of using Mesa amps I´ve used all sorts of loads, including ones NOT recommended..... And I´ve never had problems.....

If it were my amp, the very first thing I´d do is hook it right back up to 4 ohms, and if the fuse blows again it´s on it´s way to a tech... Does not function as specified: either misengineered or defective, the tech can tell you which.. and if it´s misengineered, then it´s out the door before it can close it coming in

I still say it was the tubes

i'm not ruling out the tubes...they were fairly new, but they were EL34's which i've heard aren't as rugged or reliable as a lot of 6L6 tubes. and i've also heard about mesas running hot.

but the amp worked fine when it was connected to a proper load AFTER i put in the new power tubes and fuse. the mismatch is definitely what triggered all this. i can assure you nothing else in the amp is problematic...i bought it brand new two years ago and i've babied it since day one, and i've never had a single problem with it in the past.

the whole point of my post was to encourage people to be careful to connect everything properly when you know you can, so stuff like this doesn't happen. apparently you missed that...i'm not trying to gather sympathy or advice, because the amp is working fine now.

 

[Zerberus]

Re: close call with single rectifier: impedence mismatching (long read)

.....the whole point of my post was to encourage people to be careful to connect everything properly when you know you can, so stuff like this doesn't happen. apparently you missed that........

Ehm, yes, I think not only I lost this a bit out of focus... sorry for that

Reminds me a bit of the vault thread with the beer can fuse

 

[The Golden Boy]

Re: close call with single rectifier: impedence mismatching (long read)

but regardless of what the manual says, a 16 ohm load connected to the 4 ohm tap obviously causes problems.

So if a comet goes by, and you stub your toe, the comet caused you to stub your toe?

For running a 2.67 ohm load, you use a 2 ohm setting on the amp, not the 4. Not because it's closer to 2, but because 2 is under 2.67.

I don't pretend to know the manual, but I'd lay dollars to doughnuts, that the people who engineered the amplifier and had a hand in writing the manual know a bit more about the amplifier than the average user.

Also don't forget that most tubes are made in places that aren't reknown for impressive quality control. (regardless of the reputation, GrooveTubes does not manufacture 98% of the tubes they brand, nor does Mesa)

 

[ledzepp29]

Re: close call with single rectifier: impedence mismatching (long read)

You think that's bad? I went into GC a few months ago to buy a case for my guitar. It was pretty empty so I decided to check out a few amps. The guy hands me a cable and says "just plug into whatever you want, everything should be hooked up." OK, so I noodle around on a Blues Junior for a while before the inevitable happens: I graduate over to where they have a 70's Plexi set up on top of two 1960 cabs. I turn it on, but can't get any sound of it. So I'm standing there waiting for the tubes to warm up a little longer, and the guy comes running over shouting at me to turn it off. Turns out they had the power cable plugged in but no cab hooked up! Now who's bright idea was that!? Anyway, the fuse wasn't blown, but the amp didn't work. Then I left.

similiar thing happened a couple days ago, I was at my friends and we had our stuff set up on his back deck where we could play just about as loud as we wanted. Well, I had just set down my cab and put my orange head ontop, then walked to the lake in his back yard to light some fireworks. Then I hear him yell, hey come plug in! I turn around and notice my friend, being his bass playing self, had plugged the amp in and turned it on but not bothered to hookup a speaker cable to the cab. Needless to say, I ran for him and told him to turn it off and if the amp was fried I would eat his soul. Well after I got everything "properly" set up, all was good!

 

[Zerberus]

Re: close call with single rectifier: impedence mismatching (long read)

Yeah, you either got lucky or the head has some kind of safety....

I noticed a similar "undocumented safety feature" on my 50:50 on tuesday: when both Inputs are used (l and r), the amp won´t go off standby unless both sides have a cab attached... and while not essential for the amps survival per se, with cabs on both sides it also won´t come off standby if you´re not using both inputs :headbang:

 

[muttonchopsrule]

Re: close call with single rectifier: impedence mismatching (long read)

So if a comet goes by, and you stub your toe, the comet caused you to stub your toe?

no. not at all.

i'll try to make this as clear as i can...

-amp works perfectly
-impedence is mismatched in the manner stated above
-power tubes fry
-new tubes are put in, impedence is matched properly, and the amp works again like normal

conclusion: mismatching the impedence fried the power tubes


i don't know what else i can possibly add to that, but that's what happened. if you care to argue, then go out and buy a single rectifier, put EL34's in it, and mismatch the impedence in the same way as what happened to mine. then play through it for about 15 minutes at a volume loud enough to hear over drums, bass, and a dual rectifier. then come back and tell me how it worked out for you.



i don't know why everyone wants to argue this instead of just taking it for what it's worth. maybe my words just aren't credible because i'm an 18 year old kid that doesn't own a wall of tube amps... i guess nobody can take a kid seriously these days. maybe it's just me, but if gearjonser posted this same thread, i'm sure people wouldn't be arguing him (no offense to GJ at all, i'm just using someone who has a well-respected name on this forum).


oh well.

 

[Zerberus]

Re: close call with single rectifier: impedence mismatching (long read)

no. not at all.

i'll try to make this as clear as i can...

-amp works perfectly
-impedence is mismatched in the manner stated above
-power tubes fry
-new tubes are put in, impedence is matched properly, and the amp works again like normal

conclusion: mismatching the impedence fried the power tubes

Non-scientific methods lead to false conclusions... in troubleshooting the golden rule is to NEVER, EVER change more than one parameter at a time. You did that, making all the data collected after this time or all t´collectd before USELESS in this comparison

2 things were different when it was set up "properly" (which it was before): the impedance and the tubes.... the tubes blew the first time, but not the second, ok... without blowing aother set of tubes running it at 4 ohms (which Mesa themselves, a top-notch amp tech, and an ex-mesa Dealer are all telling you will NOT cause problems), you can make NO sound judgement on this... tubes are like light bulbs, some last years, some seconds...

As I posted before, hook it up to 4 ohms and if they bowy AGAIN, THEN it´s the mismatch.... I´ll bet you a new set of tubes that they won´t

i don't know what else i can possibly add to that, but that's what happened. if you care to argue, then go out and buy a single rectifier, put EL34's in it, and mismatch the impedence in the same way as what happened to mine. then play through it for about 15 minutes at a volume loud enough to hear over drums, bass, and a dual rectifier. then come back and tell me how it worked out for you.

Been there, done that...Done it on Duals, Singles AND Triples..... never had problems, and when i test tube gear an hour ins absolute minimum

i don't know why everyone wants to argue this instead of just taking it for what it's worth. maybe my words just aren't credible because i'm an 18 year old kid that doesn't own a wall of tube amps...

For reasons stated in thes post, your conclusions are inherently flawed, and that´s the reason people are arguing with you.... Conversely, That some of these people have MUCH more experience than anyone else on the board (Jeff Seal) doesnt seem to be something that interests you either ´

i guess nobody can take a kid seriously these days. maybe it's just me, but if gearjonser posted this same thread, i'm sure people wouldn't be arguing him (no offense to GJ at all, i'm just using someone who has a well-respected name on this forum).

Totally irrelevant, why not play the black minority card while you´re at it, that way you can scream forum brutality and get off lightly... :evil:

If you hadn´t just stated this, I still wouldn´t know how old you are and still wouldn´t give a **** either.... But NOW it´s become an issue, at least to you

You´re taking a one time experience, not even trying to duplicate it, and stating the resulting flawed conclusions AS FACT into the faces of people who know the exact opposite to be true from YEARS of experience....

Analogy: If I came into a garage and said my engine blew because I pushed the brakes, the mechanigwill wonder and start asking questions.... when I tell him i kept going full speed on the gas and took out the gear, he´s gonna tell me that it was tme still standing o the gas, and not me braking..... If i turn around and tell him, constantly, without budguing, that it WAS the brakes... Well, at some point he´s going to start laughing, say "Yeah, whatever, believe what you will", and more or less blow me off...... and That´s pretty much the point you´ve taken your defense of this theory to.... to the point where the ppeople that CAN help you are starting to lose interest in doing so because of your refusal to even consider the flaws in your logic or knowledge of others

Part of being a good teacher is being a good learner and keeping an open mind for things that may be different that believed

 

[Robert S.]

Re: close call with single rectifier: impedence mismatching (long read)

Hey Mutton, a fellow Michigan guy here. I also play and have owned several Mesa amps, a couple Marshalls as well as Crate, Peavey, Musicman, Supro and others. I am not a super fancy amp tech and I dont do my own fretwork but I have managed to keep my amps running and guitars playable for more than a couple of years now and I'll try to share some of my insites into that. Take it or leave it but this is what I know through the experience of owning, playing and blowing up an amp or two over the years.

Tubes fail and it's really not that rare of an experience. A tube is really nothing more than a pair of conductive surfaces with around 400v dropped across them and another surface in between with a small voltage applied contained in a vaccum. This arrangement makes for a lot of heat and sooner or later (sometimes right from the factory - I've bought bad Mesa branded tubes) they burn up. It does not take an impedance mis-match or a component failure to kill a tube and actually tubes will take a lot of abuse before they croak. They really aren't that fragile unless you get a bad one or an old one. Most tube makers will spec tubes for 6 months to a year of use. After a year of hard service most tubes will start losing tone. It's a gradual thing over the life of a tube and you don't usually hear the difference until you change out the old tubes but it happens.

The reason your tubes died is most likely because it was their time. When a power tube croaks it often takes out the fuse, that is what the fuse is there for. As a tube fries it can draw a lot of extra current from your supply tranny and dump a lot of current on your output tranny and all the components in between. A blown fuse saves a lot in repair bills.

A couple of years ago I was playing a gig at a local club and after the sound check the soundman placed an extra mic stand behind one of my cabs to get it off of the floor and unintentionally unplugged one of my cabnets. This caused me to run one side of my mesa 2:90 into infinite resistance, which is a tad higher than the 4:1 mismatch you encountered. Needless to say, after playing the set I had a blown fuse that I didn't discover until the next day. I changed the fuse and the amp played but every couple of months I'd blow the same fuse.

I finally broke down and took my 2:90 to my amp tech after changing tubes a couple of times and deciding that tube failure was not the problem with the fuse. It turns out that in this case I had a pair of screen resistors (high wattage wire wound) that were toast. The tube in that socket was glowing bright red due to the fried resistors and was definately running way hotter than spec but would not die. God bless that little bugger for not giving up the ghost. Tubes will handle a lot more abuse than you might imagine but sometimes they just croak for no apparent reason.

Try not to judge Zerb and Jeff too harshly for their opinions. While it may seem perfectly logical to assume that your friends mistake with the impedance caused your tubes to croak, this is probably not the case. If the tubes hadn't failed you may have never known he did it. It was just unlucky timing that made him look bad.

 

[Robert S.]

Re: close call with single rectifier: impedence mismatching (long read)

Output trannies in Mesa amps are actually very sturdy and a sound guy helped prove that to me. Mesa tubes don't always last forever and occasionally they are bad straight out of the box. You just can't tell when they will croak. A bigger problem with impedance mismatches is that it can cause your speakers drivers to heat up and that can kill the drivers. Way back in the day Clapton used to mismatch his impedance because he liked the tone. He claimed to love the tone he got from doing this right up until the speakers fried.

Trust me, the guys on this forum know their stuff. They aren't disagreeing with you because you are young but instead because years of experience has proven that your assumptions might not be correct.

Either way at least you can be grateful that no real harm was done and the amp is still in proper running condition.