Vintage Marshall VS-412 Cabinet How Many Ohms???

Jethro Rocker said:
I edited my response. Set it to 8 ohms if you are in doubt
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On my custom 2x12 cabinet, the Celestion 250 watt Copperbacks are each a 16 ohm speaker.

20220304_205822.jpg

I run two separate cables to each speaker and there's a distinct tonal improvement to powering the cabinet like this.

20220321_050209.jpg

I've shared this with @ivan H and @syscokid, but I'm not sure exactly why...and yes, both speakers are running and have been verified with both connection methods.
 
Robert Herndon said:
On my custom 2x12 cabinet, the Celestion 250 watt Copperbacks are each a 16 ohm speaker.

I run two separate cables to each speaker and there's a distinct tonal improvement to powering the cabinet like this.

View attachment 82641

I've shared this with @ivan H and @syscokid, but I'm not sure exactly why...
Click to expand...
There should really be no difference. Parallel out is parallel out.
 
What amplifier is that?
If the speaker out jacks on amp are simply paralleled with connectors at the back then there is absoultely no difference in this setup. One jack runs over to the other exactly the same as on the speaker end, IF amp is wired that way. I am not privvy to that type of info.
Then it becomes placebo effect IMO.
 
Robert Herndon said:
I've always found all these variations very confusing.
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Robert, it is not confusing as it seems, once you see the explanation.


Generally, the reading given by an ohmmeter will be about 2/3 to 3/4 of the impedance of the speaker. So, a 4 ohm speaker will typically measure about 2.5 - 3 ohms, and an 8 ohm speaker will typically read about 5-6 ohms, while a 16 ohm speaker will measure around 12 ohms.

As Per Mesa Boogie: https://mesaboogie.zendesk.com/hc/e...ted-impedance-not-match-an-ohm-meter-reading-

Measuring speaker cabinets using an ohm meter will not give accurate results because ohm meters read DC resistance, not AC impedance. AC impedance will always be greater than the DC resistance,a typical 16 ohm speaker will measure approximately 12 ohms, an 8 ohm speaker will usually measure between 5 and 7 ohms and a 4 ohm speaker will usually measure between 2.5 and 3.5 ohms.


I learned a lot when I got my orange tolexed 4x12 with 4 Governor speakers in it. The switchable 2 jack mono/stereo scenario can play havoc with readings if not wired right. The previous owner had things all screwed up, like I would get 54 ohm and 26 or some really odd numbers till I rewired it right.
 
chilipeppermaniac said:
Robert, it is not confusing as it seems, once you see the explanation.


Generally, the reading given by an ohmmeter will be about 2/3 to 3/4 of the impedance of the speaker. So, a 4 ohm speaker will typically measure about 2.5 - 3 ohms, and an 8 ohm speaker will typically read about 5-6 ohms, while a 16 ohm speaker will measure around 12 ohms.

As Per Mesa Boogie: https://mesaboogie.zendesk.com/hc/e...ted-impedance-not-match-an-ohm-meter-reading-

Measuring speaker cabinets using an ohm meter will not give accurate results because ohm meters read DC resistance, not AC impedance. AC impedance will always be greater than the DC resistance,a typical 16 ohm speaker will measure approximately 12 ohms, an 8 ohm speaker will usually measure between 5 and 7 ohms and a 4 ohm speaker will usually measure between 2.5 and 3.5 ohms.


I learned a lot when I got my orange tolexed 4x12 with 4 Governor speakers in it. The switchable 2 jack mono/stereo scenario can play havoc with readings if not wired right. The previous owner had things all screwed up, like I would get 54 ohm and 26 or some really odd numbers till I rewired it right.
Click to expand...

I'm not too smart, or patient!!!

But I appreciate the information!!!!!
 
Robert, you are smart, I can understand the patient part. NOW for when lack of patience biting one in the ASP,,,,,,,,,,,,,, just try rushing things and see what happens. WE usually muck up what we are doing and it take 10x longer to fix it.

Never rush or omit checking an unknown CAB. Always make sure to MATCH impedences. Never want to ruin an amp by Ohms mis matches.

Picture a worst case scenario. NO LOAD on a Valve amp powered up. That is basically the same as taking John Force's Funny Car and running it 350 mph toward a wall and having no brakes or chute.

Picture the OHMs as the brakes and the proportioning valve for the hydraulics. I am pretty sure you understand how that works on car braking systems.
 
chilipeppermaniac said:
Robert, you are smart, I can understand the patient part. NOW for when lack of patience biting one in the ASP,,,,,,,,,,,,,, just try rushing things and see what happens. WE usually muck up what we are doing and it take 10x longer to fix it.

Never rush or omit checking an unknown CAB. Always make sure to MATCH impedences. Never want to ruin an amp by Ohms mis matches.

Picture a worst case scenario. NO LOAD on a Valve amp powered up. That is basically the same as taking John Force's Funny Car and running it 350 mph toward a wall and having no brakes or chute.

Picture the OHMs as the brakes and the proportioning valve for the hydraulics. I am pretty sure you understand how that works on car braking systems.
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When I "saw" 9 ohms on the DVOM, I stabbed the 8 on speaker out and let her rip...

LOL
 
YES a VS412 can be an 8 ohm cab. HOWEVER, during it's life, it is possible speakers were changed, 1,, 2, 3 or even 4 of the speakers could be dead or shorted etc. IT is best to VERIFY before hooking up to any amp that is not the usual amp used with that cab.

Now given my orange tolexed, 4x12, and the orange tolexed Marshall 100 Watt I got off Marketplace directly from the seller at HIS house. One might assume when the amp arrives in it's new home, that the amp and cab would be set with matching impedences. ESPECIALLY SINCE I PLAYED THROUGH THE AMP AT THE GUY'S HOUSE BEFORE BUYING IT. WRONG.

Once I got home, I did not get past taking the amp off standby before the fuse blew. Put replacement fuse in, and the other fuse blew. Heard Pop noises and decided to lambast the seller and see if he would do me a solid.

No dice.

So as folks like bdon know, I found out the Power tubes were bad, some pre amp tube(s) too. As I got new tubes, I went about testing the cab with a speaker cable and multimeter. ALL kinds of screwy readings like I said. I also hooked up my 1960A cab to the amp once I got the new tubes in and biased etc. It worked fine, no blown fuses, etc.

To ensure I would wire up the new orange 4x12 Behringer cab with Governor speakers in it, this is when I opened up my Marshall 1960A Stereo cab to verify it's readings, wiring scheme and compare it to how the new 4x12 was wired. ALL 8 speakers are 16 ohm, wired properly now, both cabs read correct for Mono and correct for Stereo as per the switchable plate in the back with 2- 1/4 inch jacks.

The Behringer yields 8 ohm stereo, 16 ohm mono
1649551127776.png

The Marshall will give either 4 ohm or 16 ohm if switched to Mono ( depending on which jack is used)
Then if switch is in Stereo, each jack yields 8 ohms on each bank of 2 speakers.

I set my amp to 16 ohm, put the switches in 16 ohm, run 1 speaker cable to the 16 ohm jack, and put tape over the stereo side of the switch and 4 ohm jack so no one can plug in and get it wrong.


1649551787099.png
 
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chilipeppermaniac said:
YES a VS412 can be an 8 ohm cab. HOWEVER, during it's life, it is possible speakers were changed, 1,, 2, 3 or even 4 of the speakers could be dead or shorted etc. IT is best to VERIFY before hooking up to any amp that is not the usual amp used with that cab.

Now given my orange tolexed, 4x12, and the orange tolexed Marshall 100 Watt I got off Marketplace directly from the seller at HIS house. One might assume when the amp arrives in it's new home, that the amp and cab would be set with matching impedences. ESPECIALLY SINCE I PLAYED THROUGH THE AMP AT THE GUY'S HOUSE BEFORE BUYING IT. WRONG.

Once I got home, I did not get past taking the amp off standby before the fuse blew. Put replacement fuse in, and the other fuse blew. Heard Pop noises and decided to lambast the seller and see if he would do me a solid.

No dice.

So as folks like bdon know, I found out the Power tubes were bad, some pre amp tube(s) too. As I got new tubes, I went about testing the cab with a speaker cable and multimeter. ALL kinds of screwy readings like I said. I also hooked up my 1960A cab to the amp once I got the new tubes in and biased etc. It worked fine, no blown fuses, etc.

To ensure I would wire up the new orange 4x12 Behringer cab with Governor speakers in it, this is when I opened up my Marshall 1960A Stereo cab to verify it's readings, wiring scheme and compare it to how the new 4x12 was wired. ALL 8 speakers are 16 ohm, wired properly now, both cabs read correct for Mono and correct for Stereo as per the switchable plate in the back with 2- 1/4 inch jacks.

The Behringer yields 8 ohm stereo, 16 ohm mono
View attachment 82661

The Marshall will give either 4 ohm or 16 ohm if switched to Mono ( depending on which jack is used)
Then if switch is in Stereo, each jack yields 8 ohms on each bank of 2 speakers.

I set my amp to 16 ohm, put the switches in 16 ohm, run 1 speaker cable to the 16 ohm jack, and put tape over the stereo side of the switch and 4 ohm jack so no one can plug in and get it wrong.


View attachment 82662
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Yep that's why I suspect it is a 12 ohm cab given the 9.2 ohm resistance which could mean cab has 2 pairs of 2x8 ohm drivers in parallel (4 ohms each pair) and each pair series together for the 8 ohm total.
One dead driver would mean a 4 ohm pair plus a single 8 in series for a total of 12 ohms which would read somewhere near 9.
Or such. If all drivers are working positively then go with 8 ohm setting. Unless again it is a SS amp.
 
Robert Herndon said:
It's just a cab at our rehearsal space that I was invited to use.

It has a single jack with no switches.
Click to expand...

Jethro Rocker said:
That 9.2 should indicate about 16 ohms. Stock cab is 8 but measured resistance of a speaker will be LOWER than impedance which would indicate 16 ohm. Which means drivers were changed.
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Robert Herndon said:
It measured 9.2ohms
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I am willing to bet there is a wire lead disconnected off one of the terminals on a speaker. This can happen especially when wired with terminal connectors that slide onto the tabs on the speakers. As I was doing all my testing before hard wiring, I had these type ends on my wires, and if one slipped off, the readings would be odd like this 9.2 reading. If at all possible, see if you can get permission to work on this cabinet, I would ask to gain access to the insides.

If you are permitted, then you can figure out things in a few ways. First, does it have recessed handles? If so, you can unscrew them and make access to the insides to either see that the wires are all connected, see if the OHMS ratings are visible on the speakers, and to see how exactly the wires are connected to the speaker terminals ( solder or push on connectors)


Or else you can figure out how to remove the front grille panel, and you will likely see each speaker has 4 screws. Unscrew the speakers with the cab lying down on it's back. then carefully lift each one out and lay them magnet up if possible. Specs and condition of things will be obvious at this point, and you can properly test the Ohms on each speaker, and even at the jack by connecting the test leads to the +/- wires on the jack.

I am sorry to beat a dead horse, but mis matched speakers or worse, UNKNOWN speakers/cabs are a major Pet Peeve of mine.
 
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