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Thread: Univox Bass Amp for HARP

  1. #1
    JMT
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    Univox Bass Amp for HARP

    I originally posted on the harp amp forum but after re-reading my original post I realized that I didn't make it clear that the renovation was to be used as a HARP AMP. That's why I was looking opinions from the harp guys about speakers sizes, mixing and matching, impedances, etc.

    Sorry if I was misleading any of you!

    Here's my original post:
    I picked up a '66 Univox Bass Amp recently. Cathode biased 2x6L6, 2x12AU7 and a 12AX7 phase inverter. The single Jensen C15N [8 ohm] got my attention as I've always wanted to have a 15" speaker amp. Of course, when I took delivery the voice coil was locked up! LOL Now that some time has passed it's a little easier to laugh. My tech has updated the electrolytics and improved the treble control. I took it to a gig last week and was amazed by the power and cut with the no name loaner 15" speaker. I've order a Weber 15F150 for it and it's turning into a fun project. I'm going to make a new baffle as I need to move the speaker location an inch or two to clear the power tubes. I was thinking that I might go ahead and cut another baffle board to experiment with another speaker configuration such as:
    2x 10
    1x10, 2x8
    1x10, 1x12
    1x12, 2x8
    I'm not a tech and I'll need some guidance, especially, on how to match speakers to the 8 ohm amp. This forum is a good place to get some informed opinions. So...fire away!....and thanks in advance!
    Jay

  2. #2
    Old Timer
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    To keep the load at 8ohms you might be limited (don't know the Univox prmary Z so can't recommed mismatching loads).

    Cathode bias usually means high current, so I'd go 2x10", if you have room to place one speaker directly above the other, more the better. Speakers will need to be 2x16ohm in parallel, or 2x4ohm in series.

    3x16 ohm speakers in parallel will make 5.3ohms...possibly a close enough match to 8ohms, taking in to account original caveat. 1x10 + 2x8 might be fine.

    I'd personally avoid 12", but that's just me, others have made them work.

    Just one question, if you like the no name 15" so much , why change it?

  3. #3
    JMT
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    Thanks, MWJB! To answer "Why?" I'm embarrassed to say that I'm one of those guys who always wants more...of everything. So...thanks for asking. Maybe I should just focus on getting it up and running with the Weber 15. Nobody that I know would ask me that question. Good reason to hang out here. I'm, obviously, not a tech but I am enjoying bringing this amp back to life with my tech.

  4. #4
    JMT
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    Cool Univox progress

    I've installed the Weber 15F150. More volume, more tone, much better bottom end and not as harsh as the no-name 15". I've taken it out to a rehearsal last weekend and a gig tonight. The Weber is sounding better and better each time I play it so I need to hold tight before any other tweaking.

    So far I'm really happy that I stayed with the 15" speaker. I thought I'd have trouble keeping up with the volume tonight but the band I played with was surprisingly moderate with the volume and they used lots of dynamics.

    I have other multiple speaker amps which are required for most of the gigs in my area. Apparently, most of the local blues players are already deaf [or stupid] so they are no longer concerned about volume or dynamics.

    Thanks to Mark for confronting me about speaker selection. No need to fix something that's not broken.

    All the best,
    Jay

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