3 8ohm speakers and one unsure

teleman177 · 08-18-2009, 12:55 PM

I have a old sonic cab which has 1 vintage 30 speaker at 8 ohms and 2 Marshall vintage speakers at 8 ohms and the fourth is an unknown impedance it has nothing but marshall written on it.

I played through this cab for two weeks with a dsl 100 head with the impedance selector set to 8 ohms.

If the ohm rating is different than 8 ohms on the fourth speaker will it damage my dsl 100 head if it was set to 8 ohms?

MartyStrat54 · 08-18-2009, 02:45 PM

Quote:

Originally Posted by teleman177

I have a old sonic cab which has 1 vintage 30 speaker at 8 ohms and 2 Marshall vintage speakers at 8 ohms and the fourth is an unknown impedance it has nothing but marshall written on it.

I played through this cab for two weeks with a dsl 100 head with the impedance selector set to 8 ohms.

If the ohm rating is different than 8 ohms on the fourth speaker will it damage my dsl 100 head if it was set to 8 ohms?

I'm assuming that you were using the 8 ohm output because the cab is wired in eight ohm series parallel. Is that correct? If so, the chances are good that the mystery speaker is 8 ohms as well.

The easiest way to check impedance is to stick a cord into the cab and use a multimeter set to the lowest "Ohm's" position. An eight ohm cab will read 5 to 8 ohms on the meter. (This is called DC resistance.) If that is what it is, then you would use the 8 ohm output on the amp.

It is imperative that you determine the actual load of your cabinet. If the mystery speaker is a 4 or 16 ohm speaker, this will throw the load off that the amp is seeing. My guess is that it is an 8 ohm speaker.

teleman177 · 08-18-2009, 08:25 PM

thanks for the reply martystrat54 I used a multimeter at the lowest setting like you said which is the 200 setting on my meter. Not the 200k setting, I came up with 21.7

I bought the cab used and I think they threw any speaker in to sell it. That's why I'm concerned about if this cab has the right impedance.

If the speaker is the wrong ohm rating compared to the others after playing through it with the dsl 100 set to 8 ohms for two weeks will it damage the head? What would be the signs of damage? Would I be able to hear if it were damaged?

MartyStrat54 · 08-18-2009, 08:50 PM

Quote:

Originally Posted by teleman177

thanks for the reply martystrat54 I used a multimeter at the lowest setting like you said which is the 200 setting on my meter. Not the 200k setting, I came up with 21.7

I bought the cab used and I think they threw any speaker in to sell it. That's why I'm concerned about if this cab has the right impedance.

If the speaker is the wrong ohm rating compared to the others after playing through it with the dsl 100 set to 8 ohms for two weeks will it damage the head? What would be the signs of damage? Would I be able to hear if it were damaged?

Here's what you need to do. For you own records, draw a schematic of how the speakers are currently wired. Then you will need to clip one wire (or pull the wire off if it has a slip on connector) on each speaker. Using the multimeter in the 200 position, check the impedance (Ohms) of each speaker and then post that information. I will then be able to tell you what you can or can't do. Also, can you say for sure that all four speakers work? Make sure that none of them read "open." The meter will flash or if it is an analog one, it will go all the way over to the left side.

I can't theorize if any damage has been done, but a 21.7 ohm cab plugged into the 8 ohm output isn't a good thing. Factors would be how hard you pushed the amp and how long you played at a time. The good thing is that the amp is still playing and you have found out about the cab.

Post the speaker info and I will get back to you.

teleman177 · 08-18-2009, 10:16 PM

.

teleman177 · 08-18-2009, 10:27 PM

I checked the speakers and the vintage 30 doesn't read the 2 marshall g12 8 ohm vintage speakers read between 2.5 and 8 and the unknown marshall speaker reads 13.7

Does the fact that the amp still plays mean that it is ok and undamaged.

Does the output transformer go when it is damaged or does it take time for it to burn out if it has damage already from this speaker load? In other words could I have possibly damaged it and it is still working for now?

If it is damaged would there be any difference in the sound of the head. Would it have a lifeless or muddy sound because of this or would the sound of the amp be unchanged?

I'm getting a 1960 cab and wont be using this one anymore.

I don't know how true this is but I heard that if the ohm rating is higher in the cab than it is on the head your ok but if you use a cab that is 4 ohms with a head that is set to 8 that it can blow the head, is this true? Would that mean that I am alright if I had a cab at 21.7 ohms and had the head set to 8 ohms?

Thanks for your help marty

American Viking · 08-18-2009, 10:46 PM

Sounds like that mystery speaker was 16ohms and whoever put it in there didn't know anything about wiring, impedances or checking to see if other speakers were blown. That's a whole lot of bad stuff going on in that cabinet. When one speaker is blown, like your Vintage30, it throws the impedance of the cabinet off which hurts your transformers. Having a mixed ohm speaker setting in there isn't good for it either so that's two no-no's in one cabinet.
If you're getting a new cab, that's great, just as long as you stay away from the other one. Learn about proper wiring and testing out the impedance of a cab and you can fix it right up with little effort and some new speakers.
As far as damage to the output transformer... Well, DSL100's can handle more abuse as far as impedance mismatching goes there is probably some wear and tear on it but if it's still playing and sounding fine to you than it's not completely shot. I've accidentally had some mishaps with my DSL and it's handled it alright as long as you recognize this stuff early on and don't continue to operate it incorrectly. I'm surprised the amp wasn't blowing any fuses. Sometimes when a transformer is damaged it will begin to sound lackluster and dull. The tubes could have had a little added stress on them too so if your tone doesn't sound as good as you think it should, new tubes are always a good first step to take before diagnosing a bad output transformer.
Hopefully everything is alright. It can still work if slightly damaged and just because it's gone through some stress in the past doesn't mean it's going to die on you soon. As long as it's operated correctly in the future it can still give you many more years of Marshall tone.

MartyStrat54 · 08-18-2009, 11:11 PM

Quote:

Originally Posted by teleman177

I checked the speakers and the vintage 30 doesn't read the 2 marshall g12 8 ohm vintage speakers read between 2.5 and 8 and the unknown marshall speaker reads 13.7

Does the fact that the amp still plays mean that it is ok and undamaged.

Does the output transformer go when it is damaged or does it take time for it to burn out if it has damage already from this speaker load? In other words could I have possibly damaged it and it is still working for now?

If it is damaged would there be any difference in the sound of the head. Would it have a lifeless or muddy sound because of this or would the sound of the amp be unchanged?

I'm getting a 1960 cab and wont be using this one anymore.

I don't know how true this is but I heard that if the ohm rating is higher in the cab than it is on the head your ok but if you use a cab that is 4 ohms with a head that is set to 8 that it can blow the head, is this true? Would that mean that I am alright if I had a cab at 21.7 ohms and had the head set to 8 ohms?

Thanks for your help marty

Okay. We have gotten somewhere now. The V30 is toast, as in "open voice coil." The G12 that reads 2.5 ohms is shot. It probably has a roasted voice coil that got really hot, but didn't open. The other G12 appears to read good at 8 ohms. The unknown Marshall that reads 13.7 is good. It is a 16 ohm speaker. So you have a good 8 and a good 16. You can't really use them together, so you can sell them and use the money towards the new cab.

I know you are really concerned about your amp, because of the mismatched load. I can understand your concern. Right now the amp is still working and that is a very good sign. There is nothing you can do to determine if any damage has been done. If you have the money, take it to a tech and explain what has happened. He can run a signal through an "O" Scope and check to see what the signal looks like before and after it goes through the output transformer. Otherwise, if the amp is working properly, consider yourself lucky.

JohnH · 08-18-2009, 11:57 PM

Your cab is a puzzle, but definately with some issues! As Marty states, I wouldnt let it near your amp again, at least not until its sussed out and fixed.

If the amp is still working fine and sounding good, then most likley its fine. Are you going to repair this cab or at least salvage the good parts? if so youll want to check which speakers actually make a sound and also have a credible Ohms reading. A 1.5V battery touched across the contacts of each seperate speaker can test to see if theres a thump. How were they wired? if the V30 went 'open circuit' (ie infinite ohms), then the speaker in series with it also would not work (even though it might not be damaged itself). The other two, being the 13.7ohm (16 ohm nominal) and and 8 Ohm, in series together would explain the 21.7 reading that you got first.

Ken · 08-19-2009, 06:20 PM

If it's a Marshall logo speaker, it's a Celestion. Why not get the code off it and look it up?

ken

MartyStrat54 · 08-19-2009, 08:05 PM

Quote:

Originally Posted by Ken

If it's a Marshall logo speaker, it's a Celestion. Why not get the code off it and look it up?

ken

True. It may end up being worth more than the whole cabinet.

teleman177 · 08-19-2009, 08:11 PM

Thank you everybody for your help and knowledge I learned a lot from you guys.

Ken where would I look up the speaker code to see what it is? I punched the code in google and nothing came up.

Ken · 08-20-2009, 02:44 PM

The code is on the speaker frame in ink. T+ some number. Google "clestion speaker codes". You might also look for a cone code; written in ink and usually hard to read...

Ken

watchtheskies · 08-28-2009, 04:34 AM

Hi teleman177, if you are strapped for cash and just want to make your cab useable, this is what I would do

1. disconnect the 2 faulty speakers but leave them in the cab
2. buy an 8 ohm load resister (you can get these from radio shack etc) these are basically a resistor embedded in a heat sink and are designed for use as speaker replacements for exactly this situation (make sure you get one that's rated high enough for your amps output)
3. wire the load resistor in series with the 8 ohm speaker to create a 16 ohm load
4. then wire this pair (8ohm resistor+8ohm speaker) in parallel with the working 16 ohm speaker to produce a total load of 8 ohms

you should now be able to use this with your amp set to 8 ohms,
not the ideal situation, but at least it will be safe for your amp

teleman177 · 08-29-2009, 07:02 PM

Thanks for the info watchtheskies it was very informative.

08-18-2009, 12:55 PM	#1 (permalink)
teleman177 Junior Member Join Date: Aug 2009 Posts: 16	3 8ohm speakers and one unsure I have a old sonic cab which has 1 vintage 30 speaker at 8 ohms and 2 Marshall vintage speakers at 8 ohms and the fourth is an unknown impedance it has nothing but marshall written on it. I played through this cab for two weeks with a dsl 100 head with the impedance selector set to 8 ohms. If the ohm rating is different than 8 ohms on the fourth speaker will it damage my dsl 100 head if it was set to 8 ohms?

08-18-2009, 08:25 PM	#3 (permalink)
teleman177 Junior Member Join Date: Aug 2009 Posts: 16	Re: 3 8ohm speakers and one unsure thanks for the reply martystrat54 I used a multimeter at the lowest setting like you said which is the 200 setting on my meter. Not the 200k setting, I came up with 21.7 I bought the cab used and I think they threw any speaker in to sell it. That's why I'm concerned about if this cab has the right impedance. If the speaker is the wrong ohm rating compared to the others after playing through it with the dsl 100 set to 8 ohms for two weeks will it damage the head? What would be the signs of damage? Would I be able to hear if it were damaged?

08-18-2009, 10:16 PM	#5 (permalink)
teleman177 Junior Member Join Date: Aug 2009 Posts: 16	Re: 3 8ohm speakers and one unsure .

08-18-2009, 10:27 PM	#6 (permalink)
teleman177 Junior Member Join Date: Aug 2009 Posts: 16	Re: 3 8ohm speakers and one unsure I checked the speakers and the vintage 30 doesn't read the 2 marshall g12 8 ohm vintage speakers read between 2.5 and 8 and the unknown marshall speaker reads 13.7 Does the fact that the amp still plays mean that it is ok and undamaged. Does the output transformer go when it is damaged or does it take time for it to burn out if it has damage already from this speaker load? In other words could I have possibly damaged it and it is still working for now? If it is damaged would there be any difference in the sound of the head. Would it have a lifeless or muddy sound because of this or would the sound of the amp be unchanged? I'm getting a 1960 cab and wont be using this one anymore. I don't know how true this is but I heard that if the ohm rating is higher in the cab than it is on the head your ok but if you use a cab that is 4 ohms with a head that is set to 8 that it can blow the head, is this true? Would that mean that I am alright if I had a cab at 21.7 ohms and had the head set to 8 ohms? Thanks for your help marty

08-18-2009, 10:46 PM	#7 (permalink)
American Viking Senior Member Join Date: Jan 2009 Location: RICHMOND, VIRGINIA Posts: 2,031	Re: 3 8ohm speakers and one unsure Sounds like that mystery speaker was 16ohms and whoever put it in there didn't know anything about wiring, impedances or checking to see if other speakers were blown. That's a whole lot of bad stuff going on in that cabinet. When one speaker is blown, like your Vintage30, it throws the impedance of the cabinet off which hurts your transformers. Having a mixed ohm speaker setting in there isn't good for it either so that's two no-no's in one cabinet. If you're getting a new cab, that's great, just as long as you stay away from the other one. Learn about proper wiring and testing out the impedance of a cab and you can fix it right up with little effort and some new speakers. As far as damage to the output transformer... Well, DSL100's can handle more abuse as far as impedance mismatching goes there is probably some wear and tear on it but if it's still playing and sounding fine to you than it's not completely shot. I've accidentally had some mishaps with my DSL and it's handled it alright as long as you recognize this stuff early on and don't continue to operate it incorrectly. I'm surprised the amp wasn't blowing any fuses. Sometimes when a transformer is damaged it will begin to sound lackluster and dull. The tubes could have had a little added stress on them too so if your tone doesn't sound as good as you think it should, new tubes are always a good first step to take before diagnosing a bad output transformer. Hopefully everything is alright. It can still work if slightly damaged and just because it's gone through some stress in the past doesn't mean it's going to die on you soon. As long as it's operated correctly in the future it can still give you many more years of Marshall tone. __________________ Transformers inside amplifiers were not originally designed to be in there, and the tube was not created for the guitar amp. ANY recommended idle current is a guideline and in no way a necessary requirement. There is no skeleton key for any tube amp.

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08-18-2009, 11:57 PM	#9 (permalink)
JohnH Senior Member Join Date: May 2008 Location: Wollongong NSW Posts: 780	Re: 3 8ohm speakers and one unsure Your cab is a puzzle, but definately with some issues! As Marty states, I wouldnt let it near your amp again, at least not until its sussed out and fixed. If the amp is still working fine and sounding good, then most likley its fine. Are you going to repair this cab or at least salvage the good parts? if so youll want to check which speakers actually make a sound and also have a credible Ohms reading. A 1.5V battery touched across the contacts of each seperate speaker can test to see if theres a thump. How were they wired? if the V30 went 'open circuit' (ie infinite ohms), then the speaker in series with it also would not work (even though it might not be damaged itself). The other two, being the 13.7ohm (16 ohm nominal) and and 8 Ohm, in series together would explain the 21.7 reading that you got first. __________________ DSL401 8412 cab Crate Powerblock 1 x 12 Vintage 30 cab '76 Shergold Masquerader '93 Les Paul Studio '83 Roadstar

08-19-2009, 06:20 PM	#10 (permalink)
Ken Senior Member Join Date: Feb 2009 Location: Arlington Heights, IL Posts: 1,170	Re: 3 8ohm speakers and one unsure If it's a Marshall logo speaker, it's a Celestion. Why not get the code off it and look it up? ken

08-19-2009, 08:11 PM	#12 (permalink)
teleman177 Junior Member Join Date: Aug 2009 Posts: 16	Re: 3 8ohm speakers and one unsure Thank you everybody for your help and knowledge I learned a lot from you guys. Ken where would I look up the speaker code to see what it is? I punched the code in google and nothing came up.

08-20-2009, 02:44 PM	#13 (permalink)
Ken Senior Member Join Date: Feb 2009 Location: Arlington Heights, IL Posts: 1,170	Re: 3 8ohm speakers and one unsure The code is on the speaker frame in ink. T+ some number. Google "clestion speaker codes". You might also look for a cone code; written in ink and usually hard to read... Ken

08-28-2009, 04:34 AM	#14 (permalink)
watchtheskies Senior Member Join Date: Aug 2009 Posts: 229	Re: 3 8ohm speakers and one unsure Hi teleman177, if you are strapped for cash and just want to make your cab useable, this is what I would do 1. disconnect the 2 faulty speakers but leave them in the cab 2. buy an 8 ohm load resister (you can get these from radio shack etc) these are basically a resistor embedded in a heat sink and are designed for use as speaker replacements for exactly this situation (make sure you get one that's rated high enough for your amps output) 3. wire the load resistor in series with the 8 ohm speaker to create a 16 ohm load 4. then wire this pair (8ohm resistor+8ohm speaker) in parallel with the working 16 ohm speaker to produce a total load of 8 ohms you should now be able to use this with your amp set to 8 ohms, not the ideal situation, but at least it will be safe for your amp

08-29-2009, 07:02 PM	#15 (permalink)
teleman177 Junior Member Join Date: Aug 2009 Posts: 16	Re: 3 8ohm speakers and one unsure Thanks for the info watchtheskies it was very informative.

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