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Thread: RTA-12B Project

  1. #1

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    Default RTA-12B Project

    I bought a set of RTA-12B speakers on Craigslist. Something is wrong with them, tweeters aren't playing. I only paid $50 for them so I'm looking at this as a project. I'm hoping the tweeters aren't blown as they are the peerless. The 3/4 amp fuses were still in and they weren't blown so I'm hoping the problem is in the crossovers. I've dug out my soldering iron, solder sucker, VOM and have a capacitor checker. Anyone have experience rebuilding the RTA-12B crossovers?

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    I assume you tested the fuses using the VOM and not just by the "naked eye" test. Also clean the fuse holders with DeOxit. You'd be surprised how far a little bit of cleaning goes also make sure the fuse holders are making good contact. Had that issue with the fuse holders on my 5B's......a simple fix.

    Remove the tweets and hook a 9V battery to the leads and see if you hear a "scratching" sound. It's odd that both tweets are shot, entirely possible, but still odd.

    Good luck

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

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  3. #3

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    Good luck with the repairs. I can't offer very much in the way of advice for this, but as a fellow RTA-12B owner I hope you can get them going to their full potential soon. Trust me, your efforts will be worth it! They are a very underated speaker.

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    The RTA-12B/C speakers have a LOT of caps. I picked up my set for $50, and like you found out the tweeters weren't working. After investigating, I found that a resistor in the crossover burned out and that the tweeters were indeed blown.

    You might have some difficulty with the tweeters if they are blown. If I am not mistaken, all the Peerless RTA-12s are mounted vertically. I had to replace my SL2000 tweeters with RDO-194s which were an exact fit (which was odd as when I had to replace the SL2000s with the same RDO194s on my Polk Monitor 10s, I had to resize the cutout). If you have to replace the Peerless with the RDOs as well, I think the mounting plate for the tweeters may have to be resized for the larger plate assembly. In this case, i would keep your eyes open for Peerless tweeters on eBay for replacements, as they appear there often.

    There are two caps in the speaker cabinets and about 10-11 in each top assembly. I decided to replace all the caps with Sonicaps. This turned out to be a very expensive endeavor as it cost over $700 and reassembly was quite cumbersome due to the size of the soniccaps.

    Even going with new Dayton or Jantzen crosscaps, the cost is going to exceed $250 total because of the crossover's complexity (I think this is the most complex crossover Polk ever made).

    I can tell you that going with the Soniccaps made a tremendous difference but $700 is an awful lot to spend on a pair of old speakers.

  5. #5

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    Unfortunately both tweeters are shot. Serial numbers 55144681 and55140882 for those that keep track.

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    Those are the American made Peerless 81 to about 83. I may have a spare pair here. keith

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    Boy, these speakers were really abused or took a lightening hit. I've tested most of the caps in one crossover that are ok but both the big inducters are fried. The insulation was falling off the leads.

    Hopefully the low frequency sections are ok.

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    See my sale add for lots of RTA12 parts. keith

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    Thanks Geppy1. Where can I find these RTA 12B parts you have?

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    The wanted section or PM me. Keith

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    Thanks Keith. Depending what I find out with checking the rest of the speaker components, I may be interested. I would guess I could make use of the 12C crossovers if you still have them. With your experience would these crossovers work on 12Bs?

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    Just won these peerless tweeters so maybe I will be able to bring the project back to life.
    Attached Images  

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    Nice!, What did they cost you?
    Polk Audio SDA SRS 1.2TL's
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    My Polk SDA SRS 1.2TL's http://www.LASAREATH.com/


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    Quote Originally Posted by rmaiers View Post
    Just won these peerless tweeters so maybe I will be able to bring the project back to life.
    Congrats-Good luck with the project.
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    I got the tweeters for $39.00. Just hope they work.

    My project continues. The MW speakers are good, the capacitors are checking out close to spec., but every stinking inductor is open and based on the condition of the insulation on the leads, they got cooked.

    Depending on whether I can get some crossover parts, I may get these things playing yet now that I hopefully have some tweeters.
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  16. #16

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    Default I may be in the same boat.

    I have found a bad LF cap on one of my RTA12b's and now will be upgrading all caps and resisters.

    Are you going to wind your own inducters?

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    I'm hoping to get another set of crossovers to use. Not wanting to get into winding my own inductors.

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    I'd like to point out something here that may be of use. If I recall correctly, the RTA12Bs are very similar to the monitor 10s. I think they both use use a pair of MW6501s and the peerless tweets. You can check my memory by looking at the schematics.

    I think if they were mine, I'd use the crossover design from the Monitor 10s because they are much simpler, use far less capacitance ($) and the crossovers are often for sale on ebay which means you can pick up some inductors on the cheap. If the crossovers work for the Monitor 10 (and they do) they should work for the 12Bs.

    I know that the crossover boards are mounted above the cabinet with the tweeters but these are your speakers now and nobody says you have to stay with the original design. You can place the caps and inductors on a piece of plastic or masonite if you get tired of glueing caps on top of caps trying to fit them on those existing boards and of course the entire board can be mounted inside the cabinet. You could even leave the existing board atop the cabinet "for looks" if you would like.
    The world is full of answers, some are right and some are wrong. - Neil Young

  19. #19

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    RTA12B uses 6600WX with Peerless or Silver SL1000 (early 84)
    RTA12C uses 6501 with SL1000 84-85 and SL2000 86-87

    I have put 6501s in my 12Bs as they seem to be slightly more open in the mdrange

    On a 10 the drivers cover 60-3000HZ. On the 12s the inner drivers cover 50-2000hz and the outer ones 50-600hz


    ts a matter of choice. Do whatever you want but,a great deal of engineering was put into the 12s. and the crossover are very complicated for a reason. From Polk ' It is actuallly two separate crossover networks used together to precisely blend the two 6600x drivers with the SL1000 high frequency radiator. In addition to impedance balancing and frequency contouring the crossover rolls of the high end of one of the 6600x drivers before the other to achieve flatter frequency response and mirror imaging. It utilizes a unique fourth order (24db/octave) Gaussian magnitude configuration which is optimized in the time domain. A computer was used to generate the basic component values but they have been listener optimized for the best sound in your room's "real world" environment. Signals are processed in realtime nearly perfectly with regard to transient information and phase coherency".

    yeah, what he said.

  20. #20

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    Geppy, Do you have any RTA 12 crossovers/parts that you are willing to sell? As I said, all the crossover inductors seem to be shot in my project 12B speakers and the resistors in the LF crossovers are shot as well. Interesting that all caps have tested ok so far. All MW speakers are ok and I have a set of peerless tweeters on the way.

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