28W from 2 x EL84s!!

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jpfampsjpfamps Frets: 2723
edited February 2018 in Amps
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  • ICBMICBM Frets: 71957
    Mesa claimed 30! The F-“30” was 2-EL84.

    I measured one and got clipping at about 22W, not surprisingly. And even that’s really hammering them on the plate voltage.

    Still, if all the solid-state companies are using output ratings that exceed the power draw now, maybe it’s just playing catch-up...

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • Depends how you measure them.

    I mean, yeah, if you use meters and science and stuff, it's a bit of a stretch - but if you whack the amp up full blast, get a mate to stand at the back of the room while you knock out a few Malcolm Young riffs and shout, "HOW MANY WATTS DOES THAT SOUND LIKE?  TWENTY-EIGHT?" ...and he nods - well, you're in...
    Not much of the gear, even less idea.
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  • jpfampsjpfamps Frets: 2723

    My guess is that MESA would have got more output power if they had increased the loading. Most manufacturers simply use the "correct" value of 8k for 2 x EL84s.

    Peavey got 50W from 4 x EL84 in the Classic 50 (ie 25Ws per pair), and I've measured a shade under this in a Traynor running 420 VDC on the HT.
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  • I thought it was pretty common to overestimate output power? My Jet City JCA50H actually puts out about 43W at the onset of clipping.
    <space for hire>
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  • ICBMICBM Frets: 71957
    I thought it was pretty common to overestimate output power? My Jet City JCA50H actually puts out about 43W at the onset of clipping.
    I depends how you measure that - 1% THD (the generally accepted figure) and 5% THD (which some guitar-amp makers use) don't sound like a lot different, but make a huge difference to the power output. Reactive vs resistive load also makes a difference.

    It can also depend on the valves - my Mesa DC-5 went up from 50W with the stock Chinese 6L6s to over 60W with some NOS JAN/Philips 7581As - which are still technically '6L6s', just very good ones.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • ICBM said:
    Mesa claimed 30! The F-“30” was 2-EL84.

    I measured one and got clipping at about 22W, not surprisingly. And even that’s really hammering them on the plate voltage.

    Still, if all the solid-state companies are using output ratings that exceed the power draw now, maybe it’s just playing catch-up...
    My co-guitarist has one and they're incredibly loud for what they are. I don't know if it's the V30 making it seem louder - very underrated imo.
    "A city star won’t shine too far"


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  • ICBMICBM Frets: 71957
    mudslide73 said:

    My co-guitarist has one and they're incredibly loud for what they are. I don't know if it's the V30 making it seem louder - very underrated imo.
    Yes, the V30 is a part of it - also the small cabinet, which makes the sound very directional so it seems loud if you're directly in line, but much less so if you're not.

    Personally, I hated it - shouty and overbearing in front, muddy and indistinct off to the side, and no real bottom end. The F-50 - which was a real 50W - was just better in every way, although admittedly heavier and more expensive.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • nick79nick79 Frets: 252
    @ICBM, i would be interested to hear your thought's on Mesa's Dyna Watt system? As far as i can tell it stores up energy then releases it when you hit a note. Gimmick or is it really a useful thing?
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  • CollingsCollings Frets: 411
    ICBM said:
    Mesa claimed 30! The F-“30” was 2-EL84.

    I measured one and got clipping at about 22W, not surprisingly. And even that’s really hammering them on the plate voltage.

    Still, if all the solid-state companies are using output ratings that exceed the power draw now, maybe it’s just playing catch-up...
    Don,t they only claim it actually delivers 30 watts for very short peaks (dyna watt or somthing).  I always thought it was just marketing bullshit.
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  • RiftAmpsRiftAmps Frets: 3113
    edited February 2018 tFB Trader
    28w in AB1 from 2xEL84 can be done if you ignore Va and Vg2 limitations.

    In fact, some Hifi guys are getting 35w from a pair of EL84s - http://www.ramlabs-musicreference.com/rm10mk2.html

    That's 35w per channel (2xEl84) or 70w Mono. Think it runs 700v on the anodes and 350v on the screens.

    My favourite tool for designing output stages shows 32.5w in real world conditions - http://bmamps.com/Tech_tds.html

    Va-k - 400V,
    Ra-a 8k,
    Vg2 - 380V
    -20V grid bias
    PD at 12w-ish

    Yes, you'll need a 40v pk-pk input to achieve, but it's not impossible.
    *I no longer offer replacement speaker baffles*
    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk

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  • DJH83004DJH83004 Frets: 196
    An awesome bit of software I agree, just amazed someone takes the time and effort to write the code and then put it out there FOC, I use it quite a bit when finding the limits of KT88s for a customer whose disco amps were designed for 60's GECs at max plate and screen grid volts (and beyond), but modern valves don't last 5 minutes and i have to tame them down!   
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  • ecc83ecc83 Frets: 1589
    edited February 2018

    The rule of thumb maximum output for valves in push-pull is 4 X pa which gives 48W for the EL84 so in theory, ~30W is possible but, although the data shows a pair of EL34s CAN deliver 100W I doubt anyone has tried?

    Re, power measurement: Minefield, we had all this swaddling when transistor PAs came out because they were feeble compared to valves and the makers had to 'massage' the figures. Thus a 5W pch ICE amp becomes a 50W "total, instantaneous, peak, music power" monster!

    For valve guitar amps I cannot see any problem in specifying Pout at 10%thd? That is after all the thd most often quoted in valve data sheets.  A 50W guitar amp is for instance SO loud through a 100dB speaker that is would not be AT 50W and 10% thd for more than mSecs and thus never be a problem. For super loud, super cleans, maybe.

    Forgot. Yes DJH, modern KT88s are not as strong as they once were!

    Dave.

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  • ICBMICBM Frets: 71957
    nick79 said:
    @ICBM, i would be interested to hear your thought's on Mesa's Dyna Watt system? As far as i can tell it stores up energy then releases it when you hit a note. Gimmick or is it really a useful thing?
    You mean like every power supply? :)

    Largely marketing bullshit, as Collings said.

    DJH83004 said:
    An awesome bit of software I agree, just amazed someone takes the time and effort to write the code and then put it out there FOC, I use it quite a bit when finding the limits of KT88s for a customer whose disco amps were designed for 60's GECs at max plate and screen grid volts (and beyond), but modern valves don't last 5 minutes and i have to tame them down!   
    I have to say I always ‘tame things down’ if possible - reliability is far more important than squeezing another dB or two out of an amp. If you really need more power, you just need a bigger amp.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • jpfampsjpfamps Frets: 2723
    ecc83 said:

    The rule of thumb maximum output for valves in push-pull is 4 X pa which gives 48W for the EL84 so in theory, ~30W is possible but, although the data shows a pair of EL34s CAN deliver 100W I doubt anyone has tried?

    Re, power measurement: Minefield, we had all this swaddling when transistor PAs came out because they were feeble compared to valves and the makers had to 'massage' the figures. Thus a 5W pch ICE amp becomes a 50W "total, instantaneous, peak, music power" monster!

    For valve guitar amps I cannot see any problem in specifying Pout at 10%thd? That is after all the thd most often quoted in valve data sheets.  A 50W guitar amp is for instance SO loud through a 100dB speaker that is would not be AT 50W and 10% thd for more than mSecs and thus never be a problem. For super loud, super cleans, maybe.

    Forgot. Yes DJH, modern KT88s are not as strong as they once were!

    Dave.

    I had a Dynachord PA amp in that output over 90W with 2 x EL34 with 800V on the plate, running predominantly class B loading.

    Musicman managed to get very high outputs from pairs of either EL34s or 6L6s running pretty much in class B with high anode voltages. I've regularly measured around 80W in these amps.

    A major concern in guitar amps running EL84s so hard would be that they are often driven hard into clipping, even at "modest" volume levels, and this is very hard on the valve screens, especially if you have increased the loading to compensate for higher anode voltage.
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