Wrong ohm setting

[Joey Voltage]

if however you didnt have any load connected at all you could fry one in a minute or so if you had the amp turned up high and were putting a signal through it

Indeed, and this is an example of one of the extremes - too high of a load, whereas the secondary load in this scenario is infinite, and this is one scenario in which you will get those nasty flyblack spikes mentioned earlier, which can puncture the wire insulation of the OT and cause the windings to short. some companies like Fender used to use a little bit of cheapo insurance by using a switched output jack, and connecting the switch lug to ground, which grounds out the OT secondary wen nothing is plugged into the output jack, giving you a closed load (the other extreme), which isn't great either as it will tax your output tubes, but it maybe the better pile of dog shit to step in

Some companies even did one better by permanently fixing a suitably large enough valued power resistor from the output jack to ground.

Marshall seems to be the worst, by not doing either, and they seem to be up there as far as reputation for this type of failure

 

[Adwex]

I fried an OT once due to a mismatch.

 

[GIBSON67]

Always check your speakers/cab with a multimeter, too! They are not always what you think they are...

I blew a diode, tube socket and both power tubes because the speaker I got for my combo was labeled as 16 ohms and actually read 8 ohms. Thank God the OT was fine.
That was the first and only time I had to take my amp to the shop.

 

[Les Moore]

Ok. But do they perform worse and worse or do they perform as usual until they brake?

 

[john l]

Ok. But do they perform worse and worse or do they perform as usual until they brake?

If I were you Id look at it like this, if you dont HONESTLY hear an audible difference then consider it good.... just dont psyche yourself out into thinking your hear or feel something going on thats not there. I myself have done this multiple times, not nessesarily dealing with trannys but the scenerios were similar. Sometimes my ears are just tired and start playing tricks on me from long listening sessions, sometimes its the room or cab, and sometimes its just me being a worry wart and making something out of nothing.

So in short. If it aint broke....

Disclaimer
Im new here and Im no tech I do have a small amount of knowledge with tube amps and most of the time I can keep my amps out of the shop on my own. Joey seems to know alot more than me and I hate people that talk out of their ass so thats as close as I can honestly get to answering your question.

 

[RickyLee]

Look at it this way, that you actually strengthened your output transformer by giving it a nice stretching out of the muscles before exercising. And now the tone is even better than before as your OT can now handle any of the normal load conditions/cranking/pushing the amp hard conditions that you will throw at it.

The power of the Mind.

The Tone is all in my Head . . .

 

[mickeydg5]

I fried an OT once due to a mismatch.

Adwex, what amp was that? Stock OT?

 

[mickeydg5]

Some companies even did one better by permanently fixing a suitably large enough valued power resistor from the output jack to ground.

Marshall seems to be the worst, by not doing either, and they seem to be up there as far as reputation for this type of failure

I always place a nice resistor across my output jack for some emergency protection.

 

[Adwex]

Adwex, what amp was that? Stock OT?

It was a stock 9005 stereo rack power amp.
The big green thing.

 

[mickeydg5]

I love you Joey, but I have to say this kind of refutes your point. If amps ARE teetering on one of two edges of too low or too high, a mismatch in the wrong direction will be MORE likely to push it over the edge and BOOM, so a mismatch in general is throwing the dice.

While my anecdotal belief is the same as yours, that most amps including Marshalls have some leeway, I also think it's not wise to put this to the test with an intentional mismatch in case it's teetering as you suggest. After all, we do have posts from people who have had catostrophic damage after a mismatch.

Ken

Ken,
the point I was trying to convey with what you quoted, was just because the user thinks they have matched the driver to the appropriate load, (ie they use the 16ohm secondary setting, when connecting to a cab that is rated for a nominal 16ohms) this doesn't mean that electrically it is what "some" would call an appropriate match, or an automatic middle ground per se, it really does depend on many determinates as stated including the intended use.

It does depend on many things as Joey stated. But leway of design as pertaining to impedance and mismatch itself is probably the lesser. Your feedback circuit also play a part with loading and matching.

Guitar players like saturation. You achieve saturation by using an output transformer that has lower maximum ratings. When the envelope is pushed on a cheaper product, you increase risk. Burnout depends more on your amp and chosen transformer than on the mismatch itself. A heavy duty transformer will have far less worries with ratings related failure. But a heavy transformer will cost way more and be much heavier.

It is better to be safe and just make sure the impedances match. Also the matching is there to benefit and make it easy for you. Matched impedances most important role is to provide maximum power transfer from your tubes to the speakers.

 

[mickeydg5]

It was a stock 9005 stereo rack power amp.
The big green thing.

Nice amp. How was it setup when the mismatch occured?

 

[RickyLee]

What is the most common cause of POWER TRANSFORMER failure?

I have seen two cases - well, I was not there or did not actually witness it. But I was given a '66 Fender Bassman many many years ago that had a bad PT. And I purchased my '83 2204 many years ago for $280 that needed a PT.

 

[Adwex]

Nice amp. How was it setup when the mismatch occured?

I was going back and forth between my 16 ohm 4x12 and my 8 ohm 2x12. Once, I forgot to change the setting. After a few minutes of playing, the amp died.

 

[mickeydg5]

What is the most common cause of POWER TRANSFORMER failure?

I have seen two cases - well, I was not there or did not actually witness it. But I was given a '66 Fender Bassman many many years ago that had a bad PT. And I purchased my '83 2204 many years ago for $280 that needed a PT.

A mains input mismatch with high wall voltage and low selector setting.

Pushing it into a pool. Really not funny.

 

[mickeydg5]

I was going back and forth between my 16 ohm 4x12 and my 8 ohm 2x12. Once, I forgot to change the setting. After a few minutes of playing, the amp died.

I like the 540R by the way.

Would that be both monoblocks into seperate speaker cabs? For how long?

Marshall OT are intended to saturate. Those are the same OT's used in the Jubilee (50 watt).

 

[RickyLee]

A mains input mismatch with high wall voltage and low selector setting.

Pushing it into a pool. Really not funny.

I played quite a few parties where our band was setup next to a pool.

But the MAINS mismatch would not be a common issue here in the States. And the high voltage MAINS/low setting, wouldn't that only do instant damage to various components and valves just downstream from the secondary?

 

[Joey Voltage]

It does depend on many things as Joey stated. But leway of design as pertaining to impedance and mismatch itself is probably the lesser. Your feedback circuit also play a part with loading and matching.

Mickey keep in mind the addition of negative voltage feedback only serves to lower the impedance of the driving stage it doesn't affect the load, or what the load reflects back to the driving stage. abundant, and even moderate Negative feedback can also cause more problems than they seem to solve as well, especially if you dont minimize phase shifts, or the open loop gain of the block simply isnt high enough. most common marshall fare uses very little thankfully.

Guitar players like saturation. You achieve saturation by using an output transformer that has lower maximum ratings. When the envelope is pushed on a cheaper product, you increase risk. Burnout depends more on your amp and chosen transformer than on the mismatch itself. A heavy duty transformer will have far less worries with ratings related failure. But a heavy transformer will cost way more and be much heavier.

I do agree on some aspects of this but not necessarily the hinted driving the ot to core saturation part of it.

is better to be safe and just make sure the impedances match. Also the matching is there to benefit and make it easy for you. Matched impedances most important role is to provide maximum power transfer from your tubes to the speakers.

But again this is a broad assumption - assuming that this was the design ideology, and was done in the first place, and what I spoke about above. (pssst most of the time time it isn't for guitar amps, Alot of them are not designed to deliver ideal power transfer).

 

[mickeydg5]

I did not mean feedback affects the loading, but works hand in hand with it. Yes, feedback must be used correctly with phasing kept in mind.

To me as plate load decreases so does power, but with an increase in total harmonic distortion. The introduction of feedback will decrease power as well as total harmonic distortion. So, if one increases plate load, the need for feedback decreases. And therefore, if she weighs less than a duck, she is a witch!

Smaller, cheaper OT's will heat up more and as characteristics approach maximum ratings, distortion increases = some degree of saturation.

Transformers are designed to match and transfer power. The effiency is what is in question here. Taps give more options. It is a simple device. (not simple to make)

Your are right, guitar amplifiers are not designed to be perfect, hince the distortion and the less than ideal power transfer.

Hey, great conversing but I shall hit the sack now.

 

[mickeydg5]

I did not mean feedback affects the loading, but works hand in hand with it. Yes, feedback must be used correctly with phasing kept in mind.

To me as plate load decreases so does power, but with an increase in total harmonic distortion. The introduction of feedback will decrease power as well as total harmonic distortion. So, if one increases plate load, the need for feedback decreases. And therefore, if she weighs less than a duck, she is a witch!

Smaller, cheaper OT's will heat up more and as characteristics approach maximum ratings, distortion increases = some degree of saturation.

Transformers are designed to match and transfer power. The effiency is what is in question here. Taps give more options. It is a simple device. (not simple to make)

Your are right, guitar amplifiers are not designed to be perfect, hince the distortion and the less than ideal power transfer.

Hey, great conversing but I shall hit the sack now.

 

[dashizzler]

If anybody cares, my amp is fine. I've played it a couple of times since at loud rehearsal volume and it sounds great. I biased it and it was a little off, as it always is after a few weeks, but it was fine. After reading everything, I remember years ago while I was touring and gigging with a band, we always used other bands cabinets and I really didn't check ohm settings!! I just plugged in and played!! I either didn't know or I was too proud to ask. I was fortunate not to have screwed anything up, or if I did, I didn't know. But then again I thought all my heads sounded like shit so I probably fried alot of power tubes over the years. Oh well.