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Deminishing Output?

Discussion in 'Amps and Cabs [BG]' started by banjo5, Oct 14, 2013.


  1. banjo5

    banjo5

    Dec 8, 2009
    Cincinnati
    So my outdoor rig is an SVT5 (which is like 1000 watts into 4) and a Mesa PH810 cab. Seems like I used to be able to knock over small kids, plow snow, move furniture, etc. with it. Here lately, it seems like it just doesn't have what it use to. I checked to make sure all 8 speakers are ok, and they seem to be. My question is, is there a chance my amp could be loosing power? Is there any way I can measure the output to detemine if it's putting out what it should be? I understand that volume or "loud" is subjective, but It seems like there should be some way to measure output power.
     
  2. georgestrings

    georgestrings Banned

    Nov 5, 2005
    FWIW, I've gigged an M-pulse 600 into a PH810 ALOT, and have never been able to crank it to even half power - and that was in a LOUD 2 guitar modern rock/metal band, with a Triple Rec halfstack on either side of the stage... I typically played with my Gain between 12 and 1 o'clock, and my Master volume around 9-10 o'clock... Once, I tried to approach 12 noon with my Master volume, and freaked out the venue owner and staff in a 400 seater - I was knocking stuff off the walls, and making bottles of booze fall - they weren't happy AT ALL...

    I'm guessing the cab isn't the issue...


    - georgestrings
     
  3. I suspect a preamp tube needs to be replaced.
     
  4. georgestrings

    georgestrings Banned

    Nov 5, 2005
    OK, I just looked into the SVT 5 Pro's specs, and it isn't anywhere near what the OP claimed(1000 watts into 4) - it's actually:

    "500W x 2 @ 2 ohms, 340 x 2 @ 4 ohms, 255 x 2 @ 8 ohms"

    It doesn't say anything about bridged capability, so I'm assuming that he's only putting 340 watts into that PH810 - and IME, Ampeg's power claims of their hybrid and SS amps are often optomistic at best... My M-pulse 600 puts out 625 watts @ 4 ohms, so I'm sure it would be significantly louder - although it is still possible that the OP has an issue with his amp - and very well may be a preamp tube on it's way out, as CL400Peavey suggested to look into...


    - georgestrings
     
  5. banjo5

    banjo5

    Dec 8, 2009
    Cincinnati
    Pre amp tube is easy enough to swap to see if that helps.

    I typically set my gain until it just just hits the preamp limiter, then set the master to the volume I need. Here lately, it seems like I'm well over 10:00 with the master, then I'm getting the output limiter light occaionally. It should be pealing paint at that level, I would think.
     
  6. banjo5

    banjo5

    Dec 8, 2009
    Cincinnati
    Here's what the manual says as far as specs go. I run it in the mono bridged mode.

    OUTPUT POWER RATING 1350 Watts Mono-Bridged @ 4 Ohms (1000 Watts Continuous)
    840 Watts Mono-Bridged @ 8 Ohms (680 Watts Continuous)
    2 x 675 Watts @ 2 Ohms (500 Watts Continuous)
    2 x 420 Watts @ 4 Ohms (340 Watts Continuous)
    2 x 255 Watts @ 8 Ohms (205 Watts Continuous)

    I can't say whether their specs are overstated or not. The other heads I've had in this power range, (including a Mesa M9) I didn't run with this cab.

    My question is really about what I perceive as a deminishing output, over the couple years I've owned this head/cab combo.

    I'll try and replace the tubes, which seems easy enough to start the troubleshooting process.
     
  7. BawanaRik

    BawanaRik

    Mar 6, 2012
    New Jersey
    With modern tubes an annual is a good idea.
     
  8. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Eh...

    :D

    Pre tubes don't last forever, but throwing out perfectly working tubes just because a year's passed is a waste of money.

    Another thing you can check is corrosion in the effects loop (spraying Deoxit in them fixes that right up), but I'd suspect a tube most of all in your case.
     
  9. I'd check that effects loop. Easiest way to check is just to plug a patch cord in from efx out to efx in. If the volume comes back with the patch cord, then Deoxit is the cure.

    In fact I'd do that before replacing the tube.
     
  10. georgestrings

    georgestrings Banned

    Nov 5, 2005
    Sorry - I just did a quick search on it, and MF's site came up - I grabbed that directly off of it... Whatever's going on, I hope you get it sorted out - it would've been interesting if you had compared it to the M9...


    - georgestrings
     
  11. Psychobassguy

    Psychobassguy Banned

    Oct 14, 2013
    Sneedville
    You'll need an oscilloscope, a tone generator and a four ohm resistor with a massive and efficient heat sink. HAM guys put their test loads for kw+ transmitters into what looks like a house paint can, but it's filled with mineral oil to conduct heat off the resistor to keep it from burning up. Using a 40Hz sine wave test tone into 4 ohms, bridged, your amp should be able to put out 63.25 volts without clipping. You can also check each side separately. They should be 41 volts at 4 ohms. It's not easy, but you'll have the answer definitively.
     
  12. Welcome back!!
     
  13. Psychobassguy

    Psychobassguy Banned

    Oct 14, 2013
    Sneedville
    I do not think my user name means what you think it does.

     
  14. Are you the same "Psychobassguy" that used to post here years ago?
     
  15. BawanaRik

    BawanaRik

    Mar 6, 2012
    New Jersey
    I've found that modern power tubes do have the long term ability the older tubes had. And while I have preamp tubes from the fifties still working it seems that the ones that die are newer.

    I would definitely check the bias after a year. If any of the tubes has drifted differently from the other it's time for a new set.
     
  16. banjo5

    banjo5

    Dec 8, 2009
    Cincinnati
    That's exactly the answer I was hoping to get, although I don't think I'm equipt to perform the test as you described. I do have one more question though, wouldn't the output voltage be effected by the output of the preamp section? You said to pump in a 40 hz sine wave, but at what amplitude, and where should the gain control be set? Or, is that a dumb question?
     
  17. WretchedExcess

    WretchedExcess

    Jul 29, 2013
    The amount of input signal voltage that's required to produce the amp's rated output, as well as the control settings that are used for testing the amp's rated output, are unique to each model of amplifier. There is no universal standard. To get the service docs for your particular amp you should contact Ampeg tech support.
     
  18. That is where the oscilloscope comes in. Flat topping (clipping) at low output levels indicates excessive gain in or from the preamp.
     
  19. I suspect not! The post was too "nice' for PBG. :D
     
  20. I received a PM, unfortunately not. I think he is on permanent ban.
     

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