Bass cabinet

Discussion in 'Amps and Cabs [BG]' started by Virgil Foreman, Dec 11, 2020.

  1. Virgil Foreman

    Virgil Foreman

    Jul 9, 2020
    Hello Everyone

    I came across a Fender Bassman 135 amp the other day that was for sale, the price was low so I bought it. I took it into my local amp repair shop to find out what I got myself into.
    The technician said the amp was in good unmolested original condition and only needed a few parts replaced due to the age of the amp, (1979). The technician asked what type of cabinet I was going to run it into. I told him that my cabinets were all 8 ohm. He said the amp would work best with a 4 ohm cab, but didn't suggest a brand.
    Here is my question to TB, what brand of cabinet would work best with this old Fender amp. I mostly play a Pbass and sometime a Rick. Most of the venues are small bars, and the occasional backyard parties.
    I've looked up bass cabinets on the WWW and the possibilities are exhausting, with no helpful information.

  2. Bent77

    Bent77 Supporting Member

    Mar 6, 2013
    Desert, Colorado
    What kind of sound are you hoping for?

    A lot of cabs are voiced for different things. If you looking for a more vintage sound, maybe the Fender cab that would have come with it or similar
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  3. Yummy Notes

    Yummy Notes Supporting Member

    Dec 20, 2019
    On the 1
    Why not run two of the cabinets you already have?
  4. Congrats on the amp!
    Bergantino NV412, NV610, NV215.
    Bergantino HG410 or 412
    These are all sealed cabs and are 4 ohm.
    Fender Bassman Pro Neo range are great too.
    From my usage of Fender Bassman amps throughout the 80s and 90s, they're pretty happy running into an 8 ohm cab.
    Better to be matched(4 ohm) of course, but my old Bassman 100 ran at 8 ohms for the 15 yrs or so and never hiccupped.
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  5. Bent77

    Bent77 Supporting Member

    Mar 6, 2013
    Desert, Colorado
    @Virgil Foreman what cabinets do you have?
    2 8 Ohm cabs would run as a 4 Ohm load
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  6. Killing Floor

    Killing Floor Supporting Member

    Feb 7, 2020
    Austin, TX
    Congrats on the amp. Pics or it didn't happen.
    Try the 2-cab suggestion to make 8 Ohm or just try a single and start low.
    Ed Byrnes likes this.
  7. Black Sabbatical

    Black Sabbatical

    May 8, 2014
    I am currently using an Avatar 12/6 4 ohm and I love it.
  8. kesslari

    kesslari Groovin' with the Fusion Cats Staff Member Gold Supporting Member

    Dec 21, 2007
    Santa Cruz Mtns, California
    Lark in the Morning Instructional Videos; Audix Microphones
    2 8 ohm cabs run together make a 4 ohm load.
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  9. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    There's nothing wrong with an 8 ohm load, the output transformer is capable of driving an 8 ohm or 4 ohm load BUT there is a trick to it.

    You need to insert an unterminated 1/4" plug into the main speaker output and connect the 8 ohm speaker to the ext speaker output. There is switching used to configure the output transformer in this amp.

    A common modification was to replace the two jacks with standard 1/4" jacks, one wired to the green wire from the transformer (the 8 ohm output) one wired to the green/yellow wire from the transformer (4 ohm output) and black wire goes to the sleeves of the two jacks which also bond to chassis ground at this point.

    Your tech should be able to do this work easily, safely and inexpensively. To run 2 x 8 ohm cabinets, you would use the 4 ohm jack and loop from one cabinet to the other for the second cabinet.
  10. Wasnex


    Dec 25, 2011
    I don't believe this is quite right.

    Here's an extract from the schematic:

    The output is 8 ohms with a center tap. So Blk to GRN-YEL is 4 ohms and BLK to GRN is 8 ohms

    If you trace through the switching, when you plug a speaker into the bottom jack, the positive terminal is connected to the GRN-YEL wire (4 ohms). I used red for the + (signal) and blue for (ground)

    If you plug into the top jack (EXT). The tip is connected to the GRN wire (8 ohms). The switching contact on the top plug is lifted, so continuity is interrupted to the GRN-YEL wire. The ring (-) is connected to the tip connector of the bottom jack (+). Normally a plug would be inserted in the bottom jack and connected to a speaker cab. This would lift the ground off the switching contact and put both cabs in series. I used red for the + (signal) and blue for (ground). Green is the series link.

    If no plug is inserted in the bottom jack, the tip connector is grounded through the switching contact....this means the ring of the top jack is also connected to ground. I used red for the + (signal) and blue for (ground)

    If you want to use a dummy plug it needs to be a shorting plug ( you would know better than I if this is necessary for long term reliability).

    Inserting the plug will lift the switching contact, so you need a shorting plug to provide continuity. The new ground path will be as follows.
    If an unterminated dummy plug is used, the amp will see an open circuit...which is very bad for a tube amp.

    Definitely unusual ;).
    Last edited: Dec 12, 2020
  11. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Yes, you are correct. It should be a shorting plug, or no plug at all (those open jack normal switches were notoriously intermittent) and I was mis-remembering the trick. It is an unusual way to do things and it's why most later amps either used an impedance switch or dedicated jacks connected to the taps themselves (like the mod I described, which is how Mesa Boogie does it).
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  12. John M Ewers

    John M Ewers Supporting Member

    Oct 17, 2018
    Forsyth, IL
    I had the earlier version of your amp, the Bassman 100. I used it with the small Fender 2-15 diagonal mounted cab with excellent results. You can find these on Reverb or in Guitar Center’s used gear listings.
    Rezdog and Winoman like this.
  13. John Webb

    John Webb Supporting Member

    Apr 20, 2006
    I like three way 12's the best...find one/try one with 4 ohm impedance.
  14. MIMike


    Jan 1, 2013
    West MI
    Hello, Virgil? I know it’s been less than twelve hours since you posted, but the question was asked twice already; what cabinets do you already have? Most likely a pair of those will work fine for you. I know, taking two cabs to a gig might be a PITA....but you just bought a 70’s tube amp, so convenience and light weight don’t seem to be a concern at this point. Almost anything combination will “work”, but if you have a pair of identical cabs, that would probably be best.
    Yummy Notes likes this.
  15. JeezyMcNuggles

    JeezyMcNuggles Supporting Member

    Feb 23, 2018
    Santa Maria, CA
    I suck, but nobody really notices
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  16. higain617


    Sep 12, 2013
    SVT 610HLF
  17. I would try to find 2 > 15" cans that are 8 ohms each. I would definitely get a few very "efficient" cabs. The Fender 135 is a 4x 6L6GC "About 100 watts" and will lose headroom quickly. I am personally using a 200 watt tube amp with efficient speakers and is plenty loud. A Bergantino NV series are only moderately efficient because they need to handle gobs of power. I have one (a 215), and my Reeves 115s x2 are a lot louder than the Berg.
  18. Wasnex


    Dec 25, 2011
    A stock Bassman 135 needs 4 ohm cabs to make max power. A pair of 8 ohm cabs would present 16 ohms to the 8 ohm output tap.
  19. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    I don't think so, not with either of the tricks I suggested which enable the 8 ohm tap.

    There MAY have been a 4 ohm only version, but the part numbers that I show for output transformers used all include 4 and 8 ohm taps. These transformers were used in other amps as well.
    Wasnex likes this.
  20. Rip Van Dan

    Rip Van Dan DNA Endorsing Artist Supporting Member

    Feb 2, 2009
    Duvall, WA
    That all-valve amp will run 8 ohms without a problem. It will also run 4 ohms all day. You have three different choices. You could 1.) just run one of your 8 ohm cabs with it, 2.)run two of your 8 ohm cabs with it (two 8Ω cabs run with parallel connection = 4Ω load), or 3.) buy a new 4 ohm cab.

    I would suggest running it with the cab(s) you have first to see how you like it. Try it with one 8Ω cab first and the with two of them. Then if you decide you'd rather get a new 4 ohm cab, take a good look at the DNS-210 by DNA. I'm one of their Endorsing Artists and I have both the DNS-210 and the DNS-410. The DNS-210 is a super clear and articulate cab with a very tight and low (34Hz) bottom end that handles far more watts then you'll ever feed it (700-watts rms). It's also a very sensitive cab and doesn't take a lot of watts to drive it.

    My guess would be that your existing cabs will work just fine with it.