Grundig console- I need some help identifying internal pieces

Discussion in 'Tube Audio' started by Onebean, Jul 6, 2018.

  1. Onebean

    Onebean AK Subscriber Subscriber

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    Nebraska
    Hi, I picked up a beautiful Grundig console for a friend, and I’m trying to figure out what all the parts are in the cabinet. I’ll comment on each picture, please help me if you can. The end goal is to have a working console stereo for my friend to put in his historically registered home.

    Here’s a shot of the outside, the wood is very beautiful, I’m casting some shadows.

    32DDCF56-71F6-4D17-8D84-F51AED46BA3A.jpeg

    The turntable with the add on SME arm is coming out. My friend wants to replace it with a full full auto turntable.

    E10EA2C0-D673-4A62-8D40-F8295E66CB39.jpeg

    Here’s the preamp with am, fm, and shortwave radio capabilities

    A88D5009-8A82-4E81-8DF9-0A843C986690.jpeg

    Saga reel to reel, I assuming this is dead. When I pulled the covers off the back, it was completely unhooked.

    F529EAD5-99C6-49F0-BBC4-9CA4054E6F22.jpeg

    I have no idea what this box does. It might be an external phono preamp. It is located under the record player with only 2 cords that plug in, and a power cord going to it. The 2 plug in cords go back to the preamp.

    FCC7DC78-4D29-439D-B8FC-548B6D24D301.jpeg

    Amp- 4 EL84 tubes, it looks like the speaker outputs are coming out of the lower left corner, the input is coming in the upper left, and the power in the middle on the right.

    7DF83FA5-CC29-439F-A409-A49206BA2065.jpeg

    Preamp- the first thing I notice is a missing tube. The gray and brown plug in wires on the lower right corner are coming from the mystery box. The previous owner said it only played on one channel. Think it’s because of the missing tube?

    4447F614-3809-416E-860E-8409D2C9BD0A.jpeg

    Mystery box #2- it had the metal cover on it. One wire is all there is, and it wasn’t connected to anything. It has a plug that looks like a 9 pin tube. It was sitting loose under the reel to reel. I can’t figure out where it would plug in except for that open tube socket on the preamp, but the cord isn’t long enough, and there is no mounting holes for it.

    EEAFAE40-E589-4F96-B2BD-4B86EA6676D4.jpeg

    Here are the decals from the back. Notice tube layout for the preamp doesn’t really match the preamp tube sockets.
    6637C8D1-E769-40CB-9799-921CE071E49E.jpeg 515B3203-9052-4942-9E67-A7261E1B3658.jpeg

    The goal is to get this fired up and see what the condition of the amp and preamp is. Then work on getting a full auto turntable retrofit in place of the existing manual turntable. If the reel to reel works, it will stay in place, if not, it will probably be removed for album storage. My friend wants to add Bluetooth, so he can stream pandora or Spotify. If I can get it going and see what the condition is, then I can decide if recapping the amp and preamp is worth the effort and expense. I’m sure the speakers will need recapped to, but the key is getting it turned on to evaluate the condition. Should I just Fire it up????


    Onebean
     
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  2. gadget73

    gadget73 junk junkie Subscriber

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    ok, so in no special order

    That PE table with the SME arm is probably a nice piece. If you swap it for a full auto, don't pitch it because you've quite probably got something worth saving there.

    Mystery box might be easier to ID with tube numbers and if you could trace the wiring in/out.

    Missing tube may be the dead channel, depends what the tube is. It may also not be a missing tube but the socket for mystery box #2

    Mystery box #2 I'm thinking is an FM multiplexer. Stereo decoder.


    Amp looks like a Grundig NF-20. Thats a damn fine amplifier.

    Don't just plug it in. Read the sticky up top about how to bring up old tube gear without having it explode on you.
     
  3. Onebean

    Onebean AK Subscriber Subscriber

    Messages:
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    Location:
    Nebraska
    Thanks Gadget, I’ll read the sticky. The previous owner played it occasionally, so it hasn’t been sitting powered down for years. I agreed to help my friend in exchange for the turntable and tonearm. I plan to try to put that into service in my system. I’ll get some better pictures of the mystery boxes and post them soon.

    Onebean
     
  4. primosounds

    primosounds SE KT120 w/ 6J5G drivers. LCLC ps + 2 x 5ar4 Subscriber

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    One way to tell if the unused socket is just a receptacle is to open up the chassis and look at the wiring underneath. That is if you don't have a picture that shows the tube layout which would also show that socket's purpose. If the empty socket is for the umbilical you should be see mostly wiring going to the pins and very few if any components like resistors and caps. It would be best if you can get a diagram of the tube layout for that chassis.
     
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  5. Onebean

    Onebean AK Subscriber Subscriber

    Messages:
    836
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    Primo, the last picture shows the tube diagram of both the preamp and amp. Sounds like the amp will need to come out.
     
  6. gadget73

    gadget73 junk junkie Subscriber

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    Looking closer at that label, it indicates 3 connections along the back. Multiplex output, Phono in, and "reverb output". That other box might be a reverb unit. Is it wired to a box that seems to be full of springs? That would be the reverb tank.
     

     

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  7. Onebean

    Onebean AK Subscriber Subscriber

    Messages:
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    Location:
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    Ok, I had some time to do some more investigation. Mystery box #1 is part of the reverb system. I found the owners manual showing the reverb set up.
    IMG_0955.jpg

    Mystery box #2 is still unidentified. I did not see anything in the manual about it. Here are some better pictures. Only one 12AU7 tube. Let me know if these pictures help decode what this is.
    IMG_0948.jpg IMG_0949.jpg IMG_0950.jpg IMG_0951.jpg

    I found these in the cabinet. I assume they are capacitors, but I'm not sure. They say original Grundig, so I assume they have been replaced.
    IMG_0952.jpg IMG_0953.jpg

    I found some schematics, and other paperwork related to the console.
    IMG_0954.jpg IMG_0956.jpg

    I'm working on getting a variac, so I can fire this up and see what works. I'm getting the feeling that my friend isn't going to want to put the money into restoring this back to original. It seem to have had some work done over the years, but I assume freshening up the amp and preamp could easily be over $500 with replacement tubes. The turntable was obviously modified, and the reel to reel appears to have been changed out at some point. Speakers appear to be original to the unit. Is it a crime against humanity to install a newer solid state receiver in this running the old speakers? How would the old Alnico speakers sound running off a newer solid state piece?

    Onebean
     
  8. century tek

    century tek Super Member

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    The chassis with the single 12AU7 tube looks to be the multiplex unit and the tuner chassis tube layout shows that the missing tube socket is in fact the socket for the multiplex adapter.

    Also those silver squares are not capacitors but rather bridge rectifiers.

    The preamp / tuner schematic and tube layout is actually spot on.

    That doesn't look to bad to recap / restore. Just change out the electrolytics on the amp, leave the tubes alone for now, and also pretty much the electrolytics in the tuner / preamplifier.
     
    Last edited: Jul 10, 2018
  9. Onebean

    Onebean AK Subscriber Subscriber

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    I have a tube tester, so I'll pull the tubes and test them. Should the reverb be eliminated for simplicity's sake? What does a multiplex adapter do? It looks like a complex board. Does it need it to work correctly?

    I can see some capacitors on the midrange speakers. I'm sure all the speaker crossovers need recapped. Any advice on this???

    Onebean
     
  10. Pio1980

    Pio1980 AK Member Subscriber

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    FM multiplex stereo adapter.
    Selenium rectifiers.
     
  11. century tek

    century tek Super Member

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    When FM stereo was just beginning, a lot of old stereo record players in this era only had mono AM/FM tuners so the sets would be equipped with an option to receive FM in stereo and would need an optional outboard multiplex adapter to receive FM stereo broadcasts. Of course anything made after 1963 ( or whenever it was) already had the multiplexing built into all receivers and tuners.
     

     

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  12. truep

    truep Active Member

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    what kind of cartridge is in the SME arm? If it's magnetic, box 1 might be a preamp. I can't imagine anyone using a ceramic cart. in an SMe arm!
     
  13. Onebean

    Onebean AK Subscriber Subscriber

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    It's an Shure V15 III, and someone added a Radio Shack phono preamp. I hadn't thought about the original being a ceramic cartridge. I will have to look and see how this is hooked into the preamp.
     
  14. gadget73

    gadget73 junk junkie Subscriber

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    The reverb should be switchable from the front panel. I'd fix it because its there. If you hate it, just turn it off.

    The FM multiplexer decodes FM stereo. Without it all FM stations are in mono.

    Fair bet the phono preamp simply sits between the record player and the original phono cartridge input. Ceramic inputs are basically line-in, so that works fine.
     
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  15. sp58

    sp58 New Member

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    Location:
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    The bridge rectifiers are rated like B250 C150 = 250vAC / 150mA, i replaced them with four 1N4007 bridged 0,01uF for every Diode.The 0,01uF reduces the switching spikes of the 1N4007, if not used, AM radio reception is very noisefull.
    On all this old german tubes i worked with, the highvoltage filter C´s after the rectifier are very good quality, never have to replace one.

    Always recap - or if done, check the four coupling C´s to the grid 1 of EL84 tubes ( around 0,1 uF ) and bias elco-c´s on the cathodes of EL84. Tubeheat is a problem for this C`s.

    Good luck !
     
    Last edited: Jul 17, 2018 at 5:32 PM
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