Kenwood TK-66 Refurbishment

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by 65W200, Feb 23, 2013.

  1. Sonic Purity

    Sonic Purity New Member

    Messages:
    4
    Looks like Moving Ahead has addressed most of the remaining questions (yay!). Having only one DMM, when i use that method, i power up, adjust one channel, power down, move test leads to the other channel, power back up and adjust the second channel.

    Unless i’m missing something, the un-addressed question remaining is what replacement trimpots to buy. Opinions may vary, and it may depend where in the world you are and what’s available to you. I’m in the U.S. and i usually order from Digi-Key, when they have something suitable. The original trimpots are so unreliable, almost anything else you might put in will be an improvement.

    I went to https://www.digikey.com/products/en/potentiometers-variable-resistors/trimmer-potentiometers/80 (actually i went to the home page and drilled down the categories to trimmer potentiometers), then started entering the fewest necessary parameters, being sure to check the In Stock checkbox. I came up with zero 30kΩ trimpots—more on that in a moment. Next i tried 500Ω. Specifically my parameters were:

    In Stock
    Mounting Type: Through Hole
    Resistance: 500Ω (this round)
    Number of Turns: 1

    I received 44 results. None exactly match what’s in there, which in this case i’d say is a good thing. My parents’ TK-66 is where it belongs in the console custom-made for it across town, so i can’t go look at exactly what was in there and measure the lead spacing. When possible, my next step would be to find one whose lead spacing is suitable. The ones with somewhat long thin wires are nice, because those can be bent to fit if they’re close in dimensions and spacing to the originals.

    Actually, it would be a good idea to include power rating. Not inclined to do a bunch of math, for this circuit i seriously doubt that any of the trimmers need to be more than 1/4W. Less might be OK, but since i don’t know, i’ll set a lower limit of 1/4W. So in the Power parameter box on the Digi-Key page, i select all options 1/4W and higher. While i’m at it, i’ll add Part Status: Active. This narrows things down to 30 options. This is where i start looking at the individual photos and lead spacing. Personally, i’m OK using any of the many very different styles of trimpot which show up in the list, so i’d likely go with best lead spacing match, and would be more inclined with something top-side adjustable. If you have a preference for tool-free hand adjustment (i don’t), that would further limit the choices.

    So what about the 30kΩ pots? Digi-Key doesn’t have any. One can go look elsewhere, or pick “close enough”. If we retain the 500Ω results and cancel the 500Ω parameter, we can see that the closest offered options are 25kΩ and 47kΩ. The Kenwood engineers may have originally picked 30kΩ because back in the late 1960s, it may have been a common, inexpensive standard value close enough. Or they may have made the choice based upon their overall circuit design showing an optimum value of 15kΩ there, and then picking a trimmer of double that value so that normally the trimpot would be set at or near the middle of its range. I’d be inclined to pick one of the 25kΩ options, expecting that the optimum setting might not be at all near the mechanical center of the trimpot’s range.

    That’s what i do, when picking a replacement for this sort of part. If i can’t get anything with leads which fit, i solder on bits of solid wire to make wire “stilts” and bend to fit. Other people have other methods/philosophies.

    That’s it (i think).

    ))Sonic((
     
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  2. djez

    djez AK Subscriber Subscriber

    Messages:
    46
    Location:
    Las Vegas, NV
    Thanks Sonic & Moving,

    Great info & as soon as I get the new pots I’ll work on the adjustments and report back.

    Thx! Dave
     
  3. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,046
    Location:
    Dallas, TX
    Just to throw in my two cents. I'd never start a diagnosis of an older analog tuner without first thoroughly cleaning the grounding contacts of the variable cap. Dirty contacts can certainly cause this type of drift. Carry on.
     
  4. Moving Ahead

    Moving Ahead Active Member

    Messages:
    323
    Location:
    Australia
    Um this wont work.......
    With Bias- when the unit is powered on the bias will fluctuate and will continue to vary until a stable operating condition is present. This takes 10 minutes. At which time final adjustments are made. Beside 2 DMM is a small investment and you won't regret it. (I actually use 4 DMM to set up before power on.)

    Yes you might find the original pots might be fine with testing. If you know how to- you should do this.

    Though with the TK series the trim pots really are flaky, and I wouldn't miss them. If the bias trim pot goes open, you'll met Puff the Magic Dragon.

    In my experience the TK is a real PITA to work on and replacing the trim pots is no walk in the park.

    FYI the distance between the outer wipers is 9mm and the leads are side by side. sealed multi-turn trim pots are best.
     
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  5. Pittosporum

    Pittosporum New Member

    Messages:
    13
    Location:
    Eastern Australia
    Hi all, great thread and for me (and others it seems) very timely, as I have recently picked up a TK-66 in very good condition, with a custom case.

    Many years in storage, so it was dusty and had the odd spider carcass, but cleaned up nicely and fully operational except a light or 2.

    I am hopeful that someone has an owners / service manual they could upload to here or Hi-Fi engine (I'm not sure what the correct protocol is for these sorts of requests).

    It seems there is a growing band of TK-66 owners that would be forever grateful. (-:

    Thanks!
     
  6. Moving Ahead

    Moving Ahead Active Member

    Messages:
    323
    Location:
    Australia
    See post 16 for a link to schematic. thats all you need. note you do have to hang 10 before you are able to press the download button.
     

     

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  7. djez

    djez AK Subscriber Subscriber

    Messages:
    46
    Location:
    Las Vegas, NV
    I want to thank Sonic and Moving for their help in dialing in this receiver. Moving's details allowed me to get to an offset of 0mV & 2.5mV putting out about 12V into 8 ohms or 18W per channel. As you can see, this is a beautiful and unique receiver that deserves a little effort. I changed all the trimpots on the amp board to multi turn, and used blue fuse style LED's that look great. Thanks for the help guys, and I'll probably be asking for more from you and others down the road soon.

    Dave
     

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  8. Pittosporum

    Pittosporum New Member

    Messages:
    13
    Location:
    Eastern Australia
    Yes thanks, have the schematic, full SM would be nice that's all.......(and no one would be able to judge how nice until one sees it)

    thanks for all the other great info BTW
     
  9. Pittosporum

    Pittosporum New Member

    Messages:
    13
    Location:
    Eastern Australia
    Great stuff, inspirational!
     
  10. Pittosporum

    Pittosporum New Member

    Messages:
    13
    Location:
    Eastern Australia
    Well I've been distracted by another restore the last couple of months.

    Lo and behold I had a look yesterday on the engine and both the Service and Instruction manuals are there in full (from 1967).

    Great manuals and much gratitude from me to the provider.
     
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