JMP 50w through a 1x12. How far can you push it?

Discussion in 'Amp Central Station' started by Chunkocaster, May 4, 2019.

  1. KC

    KC Friend of Leo's

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    I've been running a Fane M65 that I got from Avatar in a 1x12 open-back cab with Marshall & Orange 50-watt heads & it sounds great, much like a Greenback but rated at 65 watts. I never get either of the heads out of half-power mode, though. Not going for a tight modern rock sound.
     
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  2. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    Curious what year the "JMP50" is?
    While it's a model designation, it was made from '67 to IDK '76 or so, and started out lower wattage, got higher and higher topping out maybe '69- '72, then the wattage came down again.
    The middle highest wattage years will blow that V30 but it probably will take some time, unless it's an older speaker that's already been punished quite a bit.
    The earliest and latest JMP50 might let that 65w speaker live for 20-30 years.
    AFAIK a JCM800 has less wattage than the highest wattage JMP's.
    Celestion says the V30 is 70w in a closed back and 65w in an open back, so the open back isn't helping by keeping it cool.

    Turning down is one little story I tell myself when running an amp into an inadequate speaker, but I also remember that 50w is barely louder than 25w.
    My JMP50 might put out 50w with the bright volume on 2!
    Above 2 it gets louder and distorts.
    So where is 25w on the volume knob?

    Using a 25w setting is better insurance than turning the volume down, and maybe bar owners will protect your speaker as well. I doubt it's actually 25w though.
    If you use bassy fuzz pedals it's possible you could blow that speaker on the 25w setting.
    Your OT will transform 80-100w, but something in the circuit lowers what the tubes do, either a pentode triode option or a power scaling voltage reduction I'd guess.
    A fuzz can blow speakers rated higher than the amp even with a smaller OT that theoretically limits the max amount of bass that passes, which is generally what kills speakers.
    The wave form of the output effects how well the speaker handles the number of watts, and a fuzz can heat up and burn out a VC with fewer watts than the speaker rating.
    Even with the amp turned down.
     
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  3. bftfender

    bftfender Friend of Leo's

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    hey just remembered. PL2.jpg put together a jmp50 rig for some classic rock-southern project..messed with my speakers & cme up with this..the cab really is big & open..will still thump but not in metal way which is what was intended..
     
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  4. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    I'd add that playing style will also effect how much "wattage" a speaker can handle.
    You can play single note higher leads for years but then hand your guitar to a rhythm player who turns up the bass and slams out power chords and the speaker dies instantly.
     
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  5. Chunkocaster

    Chunkocaster Poster Extraordinaire

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    It's a JMP 68 50w lead clone, a ceriatone with ppimv switchable from 50 to 25watts via rear toggle. It's more amp than I need for this situation but i am about to sell my blues junior to fund a different Marhsall style 1x12 combo of around 20 watts. When I spotted the cheap price on the Blackstar 1x12 I couldn't help myself and the idea of using my head while i'm in between combos came about. If I don't like the Blackstar speaker I will just use a v30 and will be on 25 watts and lowish on the volume so should be no problems. I also wanted to know what it would be capable of.
     
    Last edited: May 4, 2019
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  6. Chunkocaster

    Chunkocaster Poster Extraordinaire

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  7. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    My feeling is that I just don't like running a 50w Marshall through a 1x12 unless it's really a high wattage speaker designed for hours of 100w operation, like a 200w EVM12L. A valuable or hard to replace speaker should not be run like that IMO.
    I think the Altec 417 is/ was rated at 70w and they blew regularly in 60w Boogies, which might make less wattage than JMP50s highest.
    Not sure what the voltages would be in a Ceriatone but likely not as high as the 500+ of the loudest JMP era.

    Some of my speakers are pretty old including a bunch of V30s, some of which have been in mid watt single 12 setups. Those would be more worn out and handle less than rated wattage!

    A v30 is disposable though, even the UK made examples are pretty cheap used.
     
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  8. Chunkocaster

    Chunkocaster Poster Extraordinaire

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    I'm a little worried doing it too but I think keeping the volume no louder than around 3 to 4 and on the 25 watt mode should be fine for just a few times. I'll give it a good test before hand just to be sure. I do have a spare v30. Just don't fancy having to install it on the spot. The speakers have some hours on them. Maybe 11 years old now and the guy I bought the 4x12 from had gigged regularly playing heavy distortion. I'll be using a v30 speaker taken from that quad cab rather than a new spare ive got.
     
    Last edited: May 4, 2019
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  9. bftfender

    bftfender Friend of Leo's

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  10. bftfender

    bftfender Friend of Leo's

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    if you were near me..come on over & bring the amp & try speakers till you hit your sound,,,but if you leave & a 4x12 with greenies ruins ya for life with a M circuit on it..i cant take responsibility for that ..lol
     
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  11. Chunkocaster

    Chunkocaster Poster Extraordinaire

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    Thanks for the offer but the airfare would kill it. One of my quads is loaded with 2 greenbacks and I have 2 new made in England greenbacks here that would end up in that 2x12 cab if I eventually get it.:)

    New in box old stock 25 watters.

    20190505_003952.jpg

    20190505_004011.jpg
     
    Last edited: May 4, 2019
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  12. bftfender

    bftfender Friend of Leo's

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    oh cool, the only think i might mention..greenies..tend to act dif in an open back..the bass seems to really woof vs being in a closed back.
     
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  13. Chunkocaster

    Chunkocaster Poster Extraordinaire

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    Thanks for the tip. The open back is optional on those 2x12 cabs. Will have to keep that in mind.
     
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  14. bftfender

    bftfender Friend of Leo's

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    fantastic,,best of both worlds !!
     
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  15. tele_savales

    tele_savales Tele-Meister

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    Correct!
     
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  16. tele_savales

    tele_savales Tele-Meister

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    I snagged a virtually brand new open back cab with a 65 watt Creamback and I've played my Friedman Smallbox thru it at about 1/2 volume (gain and master about halfway on both channels, which is pretty damn loud on the overdrive channel) and it's unreal. I got it because it was too cheap to pass up, literally 2 blocks from my house, and I figured I'd put a Redback in it, and close the 4 inch gap with some to plywood to use it w my Plexi. But it sound so nice the way it is. Really open and airy. oddly enough! V Boutique I think. It's decent sized, like 24x17 so it looks reasonable with a 50 watt head. I still need to buy more stuff, tho.
     
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  17. BobbyZ

    BobbyZ Doctor of Teleocity

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    The general rule is, use speakers rated at twice the wattage of the amp.

    However there's something else to think about. Very simply VOLUME will limit the wattage the speakers actually see. Weather you turn the amp volume down, use master volume or an attenuator, doesn't matter, they all reduced volume by reducing the amount of wattage driving the speaker(s).
    An easy to use "Watt-O-Meter" would be pretty telling and I think a lot of guys would be pretty surprised to see they're not using anywhere close to the wattage their amps are capable of.
    Plug into something small like a Deluxe Reverb sometime and play it on 10 for awhile. That's a 22 watt amp, maybe plus some cranked because it's distorting. After awhile the cops will be knocking at the door, your ears will hurt, the dog will leave and band mates will beat you to a pulp.
    So with a 50 watt Marshall odds are you'll never even hit 50 watts at the speaker, let alone how much over that it'll put out, some can do a lot more than 50! If you actually get over 20 watts I'd be surprised. (again crank a DR)

    That said, if I was in the speaker business I'd say "double the wattage". Because you never know when you might run into the damned fool that IS going to crank his amp full up.

    Oh yeah, one of my Twin Reverbs has a 25 watt Greenback and 65 watt Creamback. I'm not even remotely worried about blowing that GB. (besides it's a Chinese one :) )
     
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  18. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    At my age in a double blind test I doubt I could tell the difference between the volume of a cranked 18w Marshall and a cranked 50w Marshall...

    It's funny, my 12w brown Princeton is noticeably less loud than my 18w Marshalls, like a whole lot less loud to my ear.
    But my 18w Marshalls are not a whole lot less loud than my 50w Marshall to my ears.

    Maybe I can tolerate 12w without hearing protection but not 18w?
    Or the Marshall is putting out more watts above rated RMS watts at clipping than the Fender?

    I do recall (and repeat) a 50w Marshall I used to have that would drown out a buddy's 85w BFTR...
    Couldn't hear him at all.
    Just nuthin there until I turned the Marshall down quite a bit.

    Judging volume by ear is kind of a double edged sword.
    A 5w Champ will hurt your ears, thus a Marshall may be lour when turned way down to where it's putting out 5 watts.

    But then take something like the volume difference between 25w and 50w, which is so tiny we may not even detect it, or according to science that doubling of wattage makes the smallest increment of db change we are capable of detecting by ear.

    So on the old non master JMP we may be getting 10w output with the volume on 1 1/2, then 50w output with the volume on 2, and from 2 to 10 it goes from 50w to 70 or 80w.
     
    Last edited: May 4, 2019
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  19. BobbyZ

    BobbyZ Doctor of Teleocity

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    Yeah @telemnemonics that's where a Watt-O-Meter would come in handy!

    I got sucked into the 18 watt thing too and built one. Figured it be like my 1987 but less loud. It's one of those amps that just doesn't sound good until it's loud, too loud to be of any use to me.
    I think the kit set me back $900 or so, it's worth nothing now. That was a Weber kit, the cheapest ones at that time!
    And really the 18 watt Marshall has nothing in common with the 1987 or 1959 Marshalls anyway.
    I should've skipped it and built a tweed Fender.
     
  20. tele_savales

    tele_savales Tele-Meister

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    I was playing drums in this band, one dude had a jcm 800 half stack, the other dumbass would use his (very killer) plexi FULL STACK, near ear bleeding levels. Even the other guitarist begged him to turn down. Not. I'd never cracked a set of hi-hats until I was in that band. Oh, and a crash. And a 20" inch heavy ride I was using as a crash. Ridiculous.
     
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