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Curious Vintage Ampeg Cab & PortFlex Head Question

Discussion in 'Amps and Cabs [BG]' started by ALBnick, Feb 28, 2016.

  1. ALBnick


    Nov 19, 2011
    Hi there,
    I currently have an Ampeg PF-350 head that I run though a Peavey 410 (300W @ 4ohms). Everything works great.
    The only problem is that my band just decided to have both of our guitarists each start playing in stereo with two cabs a piece. Thus, my little 410 is no longer keeping up volume-wise. I purchased a great condition vintage Ampeg cab that has -strangely enough- two 15"s AND a 10". I'm not sure if it's a custom build or just some random model I cannot find any info about on the web. There's one input jack on the back of the cab and the plate above it has the Ampeg logo and "4 OHMS" on it. The rest of the plate's info is worn off.

    When I hooked up the new cab with my PF-350 with the master volume and gain both set at 5, the cab's volume isn't half what the same settings produce with the 410. When I increase the volume on the head to about 7, the signal starts cutting out intermittently. My initial thought is to upgrade to the PF-500 and hope that the extra wattage will solve the problem, but after perusing the web for more research I'm now learning that the cab may be the problem? I do not know the cab's RMS rating.

    So, my questions are:
    1) How can I test the RMS of the 2x15+10 cab?
    2) Is the head the problem due to volume distribution?
    3) Could the cab just be in need of repairs?

    Thanks everybody.
  2. High Camp

    High Camp

    Oct 3, 2013
    In your case, I'm almost certain that your vintage cab isn't up to the job (right now).
    Upgrading a head is always good, but now I'd focus on cabs.
    1) option one: buy new cabs
    You would be surprised about the increase in volume with two Ampeg Portaflex cabs (any kind).
    2) fix your vintage cab
    You could take a pic and post it here. I'm sure it can be identified.
    Maybe a change of speakers will do the trick and that may be cheaper than buying new cabs.
  3. Sounds like the vintage cab has problems, damaged speakers, failed crossover. A 215 would not "add" much more volume per watt than a 410, that is just a trade off. Trying for a one cab solution with a 4 ohm impedance is the fail unless that one cab is an 810 or 412. Speakers make sound, not watts. Get two good 8 ohm cabs so you can scale your volume to the gig's needs.

    The above is the answer to questions 2 and 3. The answer to question 1 is you can't. Without the original design parameters for each speaker (and derate for age/use) you would have to risk destructive testing. Speakers get "rated" for what they can accept without damage in watts. Speakers do NOT make watts.
    Last edited: Feb 29, 2016
    mbelue likes this.
  4. ALBnick


    Nov 19, 2011
    That makes a lot of sense. Thanks for the reply. My follow-up question is, would it be possible for me to run the 410 and the vintage cab together (assuming i have any repairs needed done to it) to achieve a louder sound?
  5. abarson


    Nov 6, 2003
    Santa Cruz
    Your PF350 won't go below 4 ohms safely. Both your 410 and your 215+10 are 4 ohms each, so if you daisy chained them you would be down to 2 ohms, which isn't safe for your amp.

    What kind of music do you play with two guitarists playing in "stereo"? It seems silly to me, unless it's really ambient.
    B-string likes this.
  6. It might be possible to rewire both cabs to 16 ohms. Two 16 ohm cabs together would make an 8 ohm load to the amp. Power loss (watts output) would be off set by the added speaker displacement. You would most likely windup with more actual volume than running a single 4 ohm cab.
    kosmicwizard likes this.
  7. ALBnick


    Nov 19, 2011
    We play very ambient punk/hardcore so we're trying to be as loud as possible and create a "wall of sound" (sounds more pretentious now that I read it haha). After further digging on the web, I've confirmed that the vintage cab is an SVT215E, rated at 400W @4ohms. Factor in the additional 10" in there, and I'm guessing that the RMS is closer to 600W @ 4ohms. So it sounds like the PF350 is just not capable of giving those speakers enough power.
  8. ALBnick


    Nov 19, 2011
    Also, has anyone ever heard of a 215E having an additional 10"? I can't find anything online about it so I'm assuming it must've been modded from an original 215E.
  9. I'm no Ampeg expert - and I'm not a professional in the amp business, but...

    Your 410 has a better chance of being louder and lower/deeper sounding than the old 2x15. You get in to the age and condition of the speaker, and the efficiency of both the speaker and cab design. My money's on the more modern 410.

    The 215 plus a 10"? You gotta pull a 15" out and stick your head in there to see how it was wired. Could have a crossover. Could just be thrown together. If the signal is cutting out, I'd be afraid to plug my amp in to it without testing stuff out first. Last thing you want is to fry your amp.

    Re: volume/wall of sound. If you want the cheapest bang for your buck, I've noticed beat up 810 cabs that weigh 150-200 pounds are super cheap on local CL. Who knows the condition of those speakers though. I agree, more speakers typically* means more volume. You might also consider buying a cheap power amp and a second 410 cab (4 ohm). Then either run both cabs out of the power amp (one to each side at about 4-500 watts each) or use your Ampeg head to power one of the cabs. I'd probably run both cabs off the same power amp though.

    Volume is pretty cheap these days. (tone is a separate issue...) Investigate the insides of that vintage cab you bought. See what speakers are in there and how they are wired, but I wouldn't get your hopes up too high that the vintage Ampeg cab will make it in your wall of sound.
  10. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Maybe, but Ampeg had a series of cabs called Isovents, and it sounds like you may have one of them. Could be wrong, though.
  11. basscooker

    basscooker Commercial User

    Apr 11, 2010
    cincy ky
    Owner, ChopShopAmps
    Sounds like the cab seller got a better deal...

    Definitely look inside for speaker model #s and a crossover. If all three speakers are wired up in parallel (no crossover), it's a bad mod, most likely (unless they are all 16 ohm). If this is the case, but with 8 ohm speakers, your amp is running too low of an impedance load and protection is kicking in; hence the cutting out.
  12. Doesn't it sound like it's more than 4 ohms, especially with the additional 10?
  13. This is more likely though.
  14. What do ohms sound like :D.
    mbelue likes this.
  15. Oooohhhhhhmmmmmm.....................

    B-string likes this.
  16. After that I feel I should meditate!! :D
    kosmicwizard likes this.
  17. I thought you were :D.
  18. basscooker

    basscooker Commercial User

    Apr 11, 2010
    cincy ky
    Owner, ChopShopAmps
    Stop resisting.
    High Camp likes this.
  19. Robb Fesig

    Robb Fesig

    Mar 14, 2015
    Any reason you're not looking into running stereo as well?
  20. 7D7E137B-DA6A-4A07-BCA9-EE27EE9FEDB3.
    vmabus likes this.

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