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Infinity 2000A Restoration

Discussion in 'Infinity Loudspeakers' started by pauljh, Aug 8, 2018.

  1. pauljh

    pauljh Active Member

    Messages:
    189
    Location:
    San Francisco
    My first speaker was a pair of Rectilinear IIIs (which I sold, and which are the only pair of speakers I have sold). My second speaker was the first Infinity product I could afford: the Infinity 2000. The first product, the Servo Statik 1 was a bit out of my price range as a college student. The Infinity 2000 was the precursor to the 2000A, having just two electrostatic tweeters per side, instead of four. But both used electrostatic tweeters from about 1,800Hz on up, just like their big brother, the Servo Statik 1.

    I still have the 2000s, but they haven't been played for about a decade, and something is wrong with one of the high voltage supplies. I had been intending to fix them, as an homage to my audiophile history, but I never seemed to get around to it. But then fate and eBay intervened. I saw a pair of 2000As listed, and although the cabinets looked good, and all the drivers were there, they were described as having non-operational tweeters, sold as-is and local pick-up only. They were repeatedly re-listed for a lower and lower price, and finally I made an even lower offer which was accepted. Picking them up involved a 500 mile round trip, but I visited Jocko's Steakhouse, and Hearst Castle during the trip, both things I had been meaning to do for quite a while. I figured that between the 2000s and the 2000As, I should be able to get a good working pair of some very early Infinity speakers.

    I got them home, and just as described, no sound from the tweeters.
    IMG_1602.jpg

    So I took them apart.
    IMG_1570.jpg

    Here's what the first crossover board looked like (after I removed the blown fuse):
    IMG_1568.jpg

    Hmmm, the vinyl tubing around the diodes is discolored, and the capacitors in the crossover are very modern looking polarized electrolytics. Somebody has been in here before. I also measured a few of the carbon composition high voltage bias resistors and they read 28Meg to 30Meg instead of the specified 22Meg. I decided to replace everything that was outdated, or out of spec. I planned on replacing the diodes and the capacitor in the HV supply, all (8) of the 22M carbon composition resistors with metal film ones, and replacing the electrolytic crossover caps with modern metalized film capacitors. Infinity-Classics.de had a scan of a drawing of the 2000A circuitry (attached below along with my schematic drawn from the Infinity assembly drawing), so I scoped out what I needed and ordered parts from DigiKey and Parts Express.

    After I replace the fuses and the HV supply components, there was sound from one set of tweeters, but not the other. In the second speaker, someone had once replaced the diodes and then connected the tweeter wires to the wrong terminals. After re-wiring things correctly, the second speaker's tweeters also started working. But we weren't out of the woods yet. There is an inductor in the tweeter crossover, and in the second speaker, it was not connected, as the wire had broken. I took it out of the cabinet to check it out, and found this:
    IMG_1600.jpg

    I think I need a new inductor. Maybe two. The Infinity drawing showed the inductor in series with a 2.5 ohm 10 watt resistor going to ground. My speakers had the inductor but no resistors. I measured the DCR of the roasted inductor, and got 2.5 ohms. Aha! Someone at Infinity had the bright idea to wind the inductor with really thin higher resistance wire so they didn't have to bother with the resistor. We'll save 50 cents in every speaker! What could go wrong? If you have a big amplifier and you play these speakers really loud, that inductor gets hot enough to melt its winding form. That had happened in both of my speakers. The same inductor in the 2000s crossover was the required 0.19mH value, but it had a DCR of 0.2 ohms. So I replaced the tweeter inductors in the 2000As with those from my 2000s and added some 5 ohm resistors in parallel to get the 2.5 ohm shunt to ground.

    When I was done replacing things, everything circled on this schematic was new:
    IMG_1601.jpg
    Here is what the rewired crossover board looks like:
    DSC05276-1.jpg
    Although the tweeter circuitry was now fully operational, two tweeters in each speaker were dead. Fortunately, I had bought a box of Infinity 2000A parts from eBay about 15 years ago. The box contained four working blue RTR electrostatic tweeters. I swapped out the dead tweeters for working ones, and now had a fully restored set of Infinity 2000As. I also have the original optional stands ($5 in 1970), and after I sand, prime and repaint them, I'm going to call this restoration project complete.
     

    Attached Files:

    Last edited: Aug 9, 2018
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  2. 7.62

    7.62 Gearhead Subscriber

    Messages:
    1,564
    Location:
    Las Vegas
    Nice ! Damn that inductor was Toast ! Awesome I'm glad to see us saving these speakers :beerchug:.
     
  3. pauljh

    pauljh Active Member

    Messages:
    189
    Location:
    San Francisco
    Agreed. These poor speakers were on the edge of being parted out or sent to the dump. Now they sing again.
     
  4. idadude

    idadude Well-Known Member

    Messages:
    912
    Location:
    Meridian, Idaho USA
    I enjoy seeing old speakers restored instead of being scrapped. You did some good detective work there. Kudos to you for your efforts!

    Larry D.
     
  5. pauljh

    pauljh Active Member

    Messages:
    189
    Location:
    San Francisco
    I’m wondering how many people have even heard of Infinity 2000As?
     
  6. tubed

    tubed Lunatic Member

    Messages:
    15,221
    Location:
    Aztlan
    I think I've mentioned I had a set.
    These were a curb alert in working condition.
    Like you I replaced the caps with Daytons and was concerned a bit about the discolored diode wrap. If you can do a close up, a couple diodes look burnt but weren't.
    My pair had CTS mids with the gray "metallic" Aquaplas coating.
    I think if the low frequencies were a bit better the speaker shined a lot more.
    Picture 2169.jpg
    Picture 2174.jpg
     
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  7. idadude

    idadude Well-Known Member

    Messages:
    912
    Location:
    Meridian, Idaho USA
    This is the first I'd heard of them.

    L.D.
     
  8. pauljh

    pauljh Active Member

    Messages:
    189
    Location:
    San Francisco
    I decided to replace everything I could. It was all approaching fifty years old. I recently saw an article about refurbishing KLH 9s which mentioned that the carbon composition resistors used back then were likely drifting way out of spec by now, which was certainly true in my speakers.
     
  9. swechsler

    swechsler Frog Whisperer

    Messages:
    5,006
    Location:
    7th row center
    One thing I've always wondered about these speakers - don't the high frequency cavity sides cause serious diffraction?
     
  10. pauljh

    pauljh Active Member

    Messages:
    189
    Location:
    San Francisco
    Probably. 1971 was a long time ago when just getting a flat frequency response was a major accomplishment. The tweeters are narrow and in a line so they have good horizontal dispersion and restricted vertical dispersion.
     
  11. pauljh

    pauljh Active Member

    Messages:
    189
    Location:
    San Francisco
    4D01EF1C-8964-4076-8BB0-BE6156E6DF41.jpeg FDC05381-6DDF-44EC-ABFF-ED9118B22B58.jpeg

    Old and new high voltage bias resistors:
     

     

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  12. 7.62

    7.62 Gearhead Subscriber

    Messages:
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    Location:
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    I have seen this before but I can't remember where, so I'm just curious where they connect on the speakers, guessing its to the line array?
     
  13. pauljh

    pauljh Active Member

    Messages:
    189
    Location:
    San Francisco
    These are connected to the electrostatic tweeters and provide a high voltage bias on the diaphragms.
     
  14. 7.62

    7.62 Gearhead Subscriber

    Messages:
    1,564
    Location:
    Las Vegas
    Cool, very tidy work too !
     
    Last edited: Aug 29, 2018
  15. pauljh

    pauljh Active Member

    Messages:
    189
    Location:
    San Francisco
    Here is an updated 2000A schematic with wire colors and high voltage power supply voltages.
     

    Attached Files:

  16. tubed

    tubed Lunatic Member

    Messages:
    15,221
    Location:
    Aztlan

     

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  17. pauljh

    pauljh Active Member

    Messages:
    189
    Location:
    San Francisco
    I found some Phillips midrange drivers on eBay that were in much better shape that the ones in the speakers. So I bought and installed them.
    C81088B3-CD11-4936-A2CF-331DD8796511.jpeg
    New and old midrange drivers
     
    Last edited: Sep 5, 2018
  18. pauljh

    pauljh Active Member

    Messages:
    189
    Location:
    San Francisco
    My restored 2000As sound pretty good backed up by my Modulus Servo subwoofer ;-)
     
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