How long to ruin an OT running wrong impedance?

[mickeydg5]

Plainly, anyone can match speaker to output however they want. What everyone is pointing out is "best practice".
It is a numbers game; impedances and loads; varying voltages and currents.
All parts have a main rating, wattage. If it is exceeded for too long or too abrupt things will be damaged.

There are accounts here of components, tubes, transformers being damaged and speakers blowing under certain conditions.

Normal is best and safest practice.

 

[LAARS]

Plainly, anyone can match speaker to output however they want. What everyone is pointing out is "best practice".
It is a numbers game; impedances and loads; varying voltages and currents.
All parts have a main rating, wattage. If it is exceeded for too long or too abrupt things will be damaged.

There are accounts here of components, tubes, transformers being damaged and speakers blowing under certain conditions.

Normal is best and safest practice.

..... Best practice ok.....

We have to deal with tubes that are crap. Anything that puts stress on the tubes is gonna cost you either with new tubes, or if one fails, it could cause damage.

Telling someone they have damaged the amp because they ran a safe mis-match for a few hours is not accurate information. All they did was maybe take some life off the tubes.

 

[mickeydg5]

I am not arguing any points.
After all this is the internet and everyone on it.

 

[LAARS]

Sorry Mickeydg5,
didn't mean it to sound like I thought you were arguing... Its all good. I agree with what you said, Normal is best.

 

[mickeydg5]

Sorry Mickeydg5,
didn't mean it to sound like I thought you were arguing... Its all good. I agree with what you said, Normal is best.

No sorry needed and I understood what you said.
That is not what I meant in reference to argument. I just stated or meant that I am on the sideline throwing interjections from the peanut gallery. I agree with you.

Every case can be different and all parts must be considered for that specific case.
Blanket statements on subjects like this are not a good idea so they should be avoided as to not confuse especially when considering cases with other criteria.

 

[MartyStrat54]

I burned up the output transformer on my SS guitar amp running it mismatched.

 

[Marshallhead]

A transformer won't degrade or wear out as such. What'll happen is it may fail, if the copper wire windings heat up past the melting point of the enamel insulation and it shorts, or a voltage spike burns through a spot of the insulation.

You could run a mismatch for years and suffer no ill effects. Equally you could run it for a very short time and blow the OT.

Fastest OT kill I ever experienced was a 1959HW, that had been switched on and warmed up for 5 mins on standby, switched to play, knocked out a few chords and as soon as I kicked on my TS9 and dug into one high note, it popped the OT. That was a spike incident, caused by me boosting the input signal while volume was on 10.

 

[tresmarshallz]

After reading all the stuff about mismatches about Marshalls here, it is funny to read the Mesa amp manuals that encourage mismatching to try to out different tones.
I have read this in the Mesa Caliber manual that I read recently. And it is made with a small 35 watt transformer on a 50W head with two 6L6GC tubes. How did Mesa design it to be so tolerant of mismatches to where they say mismatch is not a problem and encourage users to try different mismatches for different sound effects? I mean it is a very small and light OT on a 50W amp.

 

[wallythacker]

You're not going to see a problem or damage running a low amp load like 4 ohms into a higher impedance speaker load. Some people do this purposefully for a certain desired effect.

If it were the other way around, 16 ohm amp setting into a 4 ohm cab,
there will eventually be a problem.

This, and the following answer are amazing information to know.

Why then, isn't is common practice to set the impedance selector switch at 4 ohms the day your new head comes home?

I know with SS, running the head into higher impedance effectively cuts the output power dramatically, example, running your 8 ohm head into a 16 ohm cab truly cuts the power in half.

What's the loss with tubes? I seem to recall there is loss, but nowhere near what SS faces.

 

[wallythacker]

I'm just speculating....but in mono mode.....the right hand (looking at the back of the cab) jack is 4 ohms while the left hand one is 16 ohms. Is it possible he was running in the 4 ohm jack all along?

They are single jack 16 ohm cabs. No chance of plugging into a 4 ohm jack.

 

[wallythacker]

I don't mean to disagree with you guys, and I don't want to get anyones panties in a bunch here, so I say this with respect, please........

Can anyone actually offer "real technical information" that you "can't" safely mismatch guitar amplifiers? I'm talking from actual amp techs, or articles, not personal opinion here.

Every amp tech I personally know, (Paul Rivera-Rivera amps, and Gundolf Roy from Kitty Hawk, Evan Cantor from Bedrock amps and Trace Davis-Voodoo amps, ) has told me you can safely mismatch without any damage to the output transformer.

Been doing that since my first Marshall 1971 SLP in the early 80s. This includes JMPs, JCM800s, I'm talking a lot of my amps. 3 of these guys are the ones that have taken care of my amps since the 80s until now. So why would these guys all say its ok if it really is bad?

I recall my electronics teacher in grade 9 saying something to this effect. But someone then asked why if it doesn't matter are there devices with specific impedances. I don't remember his answer.

(I'm still figuring out multi-quote, I'm pretty much computer 'tarded.)

 

[Micky]

I know for me, I am getting very tired of explaining that the tubes and OT are not really designed to be mis-matched. I have tried and tried, as well as referred to other posts by more knowledgeable repair techs to explain that the mismatch creates a problem. As I have stated previously, do the math.
If you can't figure it out, and if you cant tell that SS amps WITHOUT output transformers are very different, then maybe you don't deserve to own a tube amp. It is obvious that those who choose to mismatch their amp to the load haven't a clue as to what might be going on.

But then again, it is your amp. Do what you want. But don't ask me for advice on how to fix it... I'm done.

 

[FutureProf88]

After reading all the stuff about mismatches about Marshalls here, it is funny to read the Mesa amp manuals that encourage mismatching to try to out different tones.
I have read this in the Mesa Caliber manual that I read recently. And it is made with a small 35 watt transformer on a 50W head with two 6L6GC tubes. How did Mesa design it to be so tolerant of mismatches to where they say mismatch is not a problem and encourage users to try different mismatches for different sound effects? I mean it is a very small and light OT on a 50W amp.

Look at Fender OT's. I have a '67 Bassman 50 and it's OT is tiny compared to my 2204. Yet people routinely mismatch Fenders and before I knew my amp was 4 ohm (I always thought that Bassman heads were 8 ohm for some reason - I was ~20 so be kind) I ran the thing into 8 ohm cabs all day long with the volumes wide open and being driven by a Boss OD pedal.

I will say again, if the amp works now, I wouldn't worry about it. For future reference, everything I have ever read or been told says match impedances - ESPECIALLY with Marshalls.

I can't imagine that Mesa would encourage mismatching loads, but if they do then they do. Don't Mesas run their output sections kind of cool? That could account for the smaller transformer being ok.

 

[Marshallhead]

My 2000 series 200 watt head went out on loan last week, and was set up and sound checked briefly with the head on 4 ohms into two 4 ohm cabs!

Thankfully I was guitar teching and arrived shortly after, giving me the chance to fix it before it was used in anger, but it's brief outing on 2 ohms did no harm. Good job, a blown OT would have been irreplaceable in that thing.

 

[stalefish]

What about if you're using an attenuator? Does the amp still "see" the cab or does it only see the attenuator? Say you set your amp to 8 ohms, use an 8 ohm attenuator, and hook up to a 16 ohm cab? Would that blow things up or create a hole in the space/time continuum?

 

[LAARS]

After reading all the stuff about mismatches about Marshalls here, it is funny to read the Mesa amp manuals that encourage mismatching to try to out different tones.
I have read this in the Mesa Caliber manual that I read recently. And it is made with a small 35 watt transformer on a 50W head with two 6L6GC tubes. How did Mesa design it to be so tolerant of mismatches to where they say mismatch is not a problem and encourage users to try different mismatches for different sound effects? I mean it is a very small and light OT on a 50W amp.

My point exactly. I don't know Randall personally, but the others who's amps I have used live, and use now I do know. They all have said to me the same thing. You can match the amp and cabs ohms, or run the amp lower in ohms then the cab. It's their amps, and they know what is safe and not safe.

I would like to hear what Zachman has to say about this topic. We seem to know a lot of the same people and use the same gear. You out there Zachman?

 

[LAARS]

I know for me, I am getting very tired of explaining that the tubes and OT are not really designed to be mis-matched. I have tried and tried, as well as referred to other posts by more knowledgeable repair techs to explain that the mismatch creates a problem. As I have stated previously, do the math.
If you can't figure it out, and if you cant tell that SS amps WITHOUT output transformers are very different, then maybe you don't deserve to own a tube amp. It is obvious that those who choose to mismatch their amp to the load haven't a clue as to what might be going on.

But then again, it is your amp. Do what you want. But don't ask me for advice on how to fix it... I'm done.

Hi Micky,
You see the problem here is, the guys that built the amps that I've used (endorsed) for the last 30 years have all stated differently. I would call them tops in their field. I have no idea who anyone up here is, giving out advice to the poster. It could be a 16 year old who doesn't have a clue.

So then you read a statement like "you don't deserve to own a tube amp" instead of showing actual tech support for why these guys that are top in the amp field are wrong, one might question the information being posted. Does that make sense to you?

If your an amp tech, great, please re-educate me, I'll owe you one. I'm being honest.

 

[Micky]

I said I was done.

And LAARS, I am not singling you or anyone else out, my statements remain that it is just a matter of time before damage is done. Tube amps are different than SS amps where yes, you can run a higher load without problem.

The fact remains that the math (yes I am an Engineer) proves that a mismatch creates problems. Search Jon Wilder (Wilder Amplification) posts for the exact math, I am not going to attempt to recreate it here. I have posted links and other references time and time again, and he would back me up when I say the above that damage will occur, maybe not right away, but running a mismatch presents problems the circuit was not designed for.

Again, do what you want. My stuff works great, and has for a very long time. I really don't care about anyone else's stuff where it has been abused. (yet another reason to not buy used amps...) I have replaced enough OT's and finals to know that misuse causes damage. Sorry if anyone else disagrees with me.

I will say the same as others, show me the math where you can prove it does no damage...

 

[MartyStrat54]

I was talking about transformers with Mickeydg5 and he had this to share with me.

Modern transformers are more efficient than vintage so ratings go much further, if that makes sense. The average transformer is probably over-designed and overbuilt by 40% to 50%. So it is quite possible that your 45W transformer is more capable of handling 65 watts.

Some guitar amplifier manufactures looking for added saturation may consider a 30W production transformer sufficient in a "guitar amplifier" design, especially if the design model is for that vintage groove or blues rock sound.

That last paragraph of Mickey's is pertaining to his explanation about how guitar amp manufacturers will actually use a lower rated OT instead of basing the size of the OT on the amps rated wattage.

Mickey also states that under-sizing is purposely done to achieve a classic, bluesy tone.

A lot of guys know how big of an impact changing an OT can be. However, I did not know that info regarding using under-sized OT's for a particular tone. I did not know that the wattage rating of an OT needs to be considered when designing an amp for a particular tone. Very interesting.

My thoughts are that modern made transformers have advanced insulation on the wire and in the case of the OT it allows hotter operation and therefore allowing you to run a mismatch (which causes heat).

 

[Blacque Jacque]

It will also partly depend on having good output bottles.

A load mismatch will cause excess power that is not delivered to the load to be reflected back into the system. Some will be dissipated in the transformer, some in the tubes themselves.