4-12 cabinet (2) 16ohm-(2) 8ohm celestions.

[Jeff'sBest]

I have a JMD1 100w head,powering a 4x12 cab. It has 2-!6ohm 60w, and 2-8ohm
25w celestions. wired in series-parallel. Question: can i run them at 16ohm or 8ohm
outputs?

 

[fitz]

I have a JMD1 100w head,powering a 4x12 cab. It has 2-!6ohm 60w, and 2-8ohm
25w celestions. wired in series-parallel. Question: can i run them at 16ohm or 8ohm
outputs?

to the forum.
Do you have a multi-meter to measure the actual resistance ohms on the cab output?
This reading is usually a little lower than the impedance rating.
One 16 ohm and one 8 ohm in parallel is 5.33 ohms - series a pair of those and you'd get 10.66 ohms.
Resistance reading on a meter would probably read in the 9 to 10 (ish) range...
If you're getting a reading something like that, or just want to skip the whole checking this stuff thing, set the amp on 8 ohm.

 

[Jethro Rocker]

Depends which are series and which are parallel.
Either way it will be an "odd" impedance not 16 or 8. Plus some speakers will get more power than others.
I guess either way 8 is safe

 

[Jeff'sBest]

Thanks for the help,Ive been running them out of the 16ohm speaker jack, but have been leary
It has (jmd1) a 8ohm,and a 16 ohm jack.

 

[fitz]

Thanks for the help,Ive been running them out of the 16ohm speaker jack, but have been leary
It has (jmd1) a 8ohm,and a 16 ohm jack.

The combined impedance from your speaker mismatch is somewhere in between 8 & 16.
Either way is far better than no speaker load at all.
The amp and speakers would probably sound better matched up with a proper 8 ohm or 16 ohm cab on the appropriate transformer tap.

 

[RLW59]

There are several different ways you could wire them series/parallel.

In at least some of the permutations (maybe all of them) the 8 ohm speakers will draw 2/3 of the amp's power. At full volume those 25w speakers will get 33 watts each. (Many Marshalls actually exceed their ratings when driven into power tube distortion -- could be more like 50 watts each at max volume.)

Safe at moderate volumes, and depending on the efficiency difference between the two types of speakers the mismatch might give good balance.

But wattage:volume is logarithmic and you can go from safe to too much quickly.

 

[Jeff'sBest]

Heres how there wired.

 

[fitz]

Heres how there wired.

Can you post a photo of that?
Have you put an ohms meter on the jack?

- the bottom pair of 8 ohm GBs are series wired to 16 ohm.
- then that's parallel wired to a series loop with the top two 16 ohm v30's at 32 ohm???
- I think that's back to the 10.66 ohms, but that's a strange way of doing it...

 

[Jethro Rocker]

Can you post a photo of that?
Have you put an ohms meter on the jack?

- the bottom pair of 8 ohm GBs are series wired to 16 ohm.
- then that's parallel wired to a series loop with the top two 16 ohm v30's at 32 ohm???
- I think that's back to the 10.66 ohms, but that's a strange way of doing it...

Yeah odd but still 10.66 ohms. So set it at 8 and there are compromises in output with different speakers as mentioned above.with that wetup not much else you can do.

 

[Scumback Speakers]

The 8 ohm speakers will get 2/3 of the power, while the 16's will get 1/3. The cab will sound "weak" with the ohms mismatch, though. I know this from personal experience with a cab I bought used that had the same setup. Had the 8's reconed as 16 ohm models, then it kicked butt.

 

[fitz]

The 8 ohm speakers will get 2/3 of the power, while the 16's will get 1/3. The cab will sound "weak" with the ohms mismatch, though.

So, not a great idea to slam the 50w's of greenbacks with 2/3's of a 100w amp.
I'd put some 16 ohm speakers in there with a little higher power handling instead of the greenbacks.
That'd solve a couple of issues.

 

[Jeff'sBest]

Im inclned to agree with you fitz. I played thru it yesterday ,in the 8ohm jack, Its definitely weaker,but it varies by the guitar volume.
I was worried more by damaging the head. The sound growls,like a beast wanting to come out. Very marshallistic,if you know what i
I mean. Just got these greenbacks on ebay for $280, cant swap for 16ohm. They dont have em. So Ill get some 16 grreenies and that"ll
be that.

 

[Jeff'sBest]

Or vintage 30 16ohm-60w. Like the other 2 on top.

 

[fitz]

Im inclned to agree with you fitz. I played thru it yesterday ,in the 8ohm jack, Its definitely weaker,but it varies by the guitar volume.
I was worried more by damaging the head. The sound growls,like a beast wanting to come out. Very marshallistic,if you know what i
I mean. Just got these greenbacks on ebay for $280, cant swap for 16ohm. They dont have em. So Ill get some 16 grreenies and that"ll
be that.

Or vintage 30 16ohm-60w. Like the other 2 on top.

If you like the GB's. another pair of 8 ohm to replace the V30's in the 412 for an all 8 ohm GB cab.
Perhaps find a 212 cab with some 8 ohm's you could swap, and put the V30's in the 212.

440 Live 2X12 guitar speaker cabinet 2019 Black with (2) Celestion Greenbacks 8 ohm 25 watts each | Reverb

New Greenbacks in a new cabinet. Don't need it since I got a twin.

reverb.com

 

[Jeff'sBest]

sounds good, thanks everyone for the help. Much appreciated!