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UNPLANNED DOWNTIME: 12th Oct 23:45

Checking Ohm on a Marshall Cab - Now Done & Updated !

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gubblegubble Frets: 1681
edited August 2023 in Amps
I recently purchased a Marshall head which came with a Marshall 8222 2x12 cab and would like some advice on checking or even changing the Ohms.

Before plugging it in i decided i wanted to check the Ohms as there's a handwritten sticker which says 16ohms and i don't want to damage anything:

The back looks like this (stock image from the internet) albeit with a sticker saying 16 ohms



to test I've plugged a speaker cable into the socket and used a digital multimeter on the other end of the cable - whilst plugged into one side i get a reading of roughly 8 Ohms and on the Other i get a reading of 4 Ohms.

I'm guessing this is in fact not a 16 ohm cabinet and the sticker is a ruse ! Or i'm a complete moron who can't work out how to measure impedance (entirely possible)

Does anyone know if it's possible to re-wire the speakers in there to make the cab 16 ohms? This would be better for the two valve heads i currently have.......

Ta in advance

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Comments

  • mrkbmrkb Frets: 5594
    Looks like they’ve rewired the cab to have two 8 ohm speakers in parallel (4 ohms) rather than series (16 ohms). It’s a simple task to rewire it.
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  • ICBMICBM Frets: 69426
    Yes, if you’re metering 8 ohms (or usually 6-7 ohms, which is the DC resistance) in the left socket and 4 (usually around 3) in the right, it has a pair of 8-ohm speakers.

    But given that it’s obviously been changed at some point and you’re going to rewire it anyway, I would open it up - or at least take the jack panel out and look inside (which is also the easiest way of pulling the back off without trying to lever it out at the sides) - and check what the speakers are… type, impedance and power rating. You should confirm this before connecting an amp to the cab - there can be some real surprises in second-hand cabs :).

    Rewiring it to 16 ohms is easy, but not if you want to retain the stereo inputs, so I would probably just use one jack, to avoid confusion. For 16 ohms, connect the jack tip to the + terminal of one speaker, the jack sleeve to the - terminal of the other speaker, and the two remaining speaker terminals to each other. You can use the existing wiring and push-connectors if you solder two of the wires together and tape (or heatshrink, if you have it) the joint. Or use a single electrician’s ‘chocolate block’ screw terminal if you don’t have a soldering iron.

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  • gubblegubble Frets: 1681
    Thanks for the help guys - finally got round to looking at doing this and turned out to be a really easy job. 

    Turns out the speakers inside are 2x 8 ohm Celestion G12T  with Marshall written on the bottom - no idea if they're good/bad/indifferent but they sound ok for my purposes.

    Whilst I was at it I decided the cab would look better as a vertical cab so removed the Marshall logo and placed it accordingly. 

    I'm rather happy with the results, the old logo shadow on teh grill is slightly annoying but only really noticeable head on:



    At a different angle i don't think you can really tell:


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