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911 Kenwood KT-7500 Lighting Issue's

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by Kenny*G, Oct 12, 2018.

  1. Kenny*G

    Kenny*G AK Subscriber Subscriber

    Messages:
    68
    Location:
    Dickinson, Texas
    Ok this is one of those simple jobs that's turning into a PIA unfortunately. I replaced all three of the lamps for the meters and dial face with 8V LED's from a highly recommended source. Changed all three, installed exactly like the originals were ( which is in series ), turned the unit on and all three lit up but one of the side bulbs had a slight flicker, almost not noticeable. They staid on for a little over an hour, all three went out. So I'm thinking the one that had the slight flicker may be the problem so I changed it out with a new spare and nothing still. I did some voltage checks and they are as follows.
    PIN 19 to 20 reads 28.5 vac
    Pin 19 to 21 reads 30.9 vac
    Pin 19 to 22 reads 34.7 vac
     

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  2. Blue Shadow

    Blue Shadow I gotta get me a new title

    Messages:
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    Lamp circuit from the Schematic on HFE.

    KT-7500 Lamps.jpg
     
  3. Kenny*G

    Kenny*G AK Subscriber Subscriber

    Messages:
    68
    Location:
    Dickinson, Texas
    Thanks, already saw that, still have no clue what the issue is. I'm a rookie.
     
  4. Blue Shadow

    Blue Shadow I gotta get me a new title

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    I posted it so folks that drop in to help don't have to go hunt it down. Hope it helps get you some answers.
     
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  5. SicMan

    SicMan Fire up those speakers Subscriber

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    If they are leds only then it's possible they will burn out.
    Some or most of them need a resistor or a resistor/diode combo like the ones available on epay

    John
     
  6. petehall347

    petehall347 the brandy coffee man Subscriber

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    rb103 likely needs changing to much higher value
     

     

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  7. hopjohn

    hopjohn Silver Face Subscriber

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    I don't wanna sound like a grumpy old man, but I'm going to anyway. LEDs and AC current aren't friends. Yes, there are ways to make it work (putting in a full bridge would be one), but I don't see the appeal of an uninviting bright green glow in vintage gear. Save that for your kids R/C drone. Install some wedge sockets boots like these and add some 8V 250mA or 300mA wedge based incandescents and be done with it. When they burn out in 5 years pop in some new ones. Meh. Now get off my lawn.
     
  8. SicMan

    SicMan Fire up those speakers Subscriber

    Messages:
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    also the reverse breakdown voltage may be too high for the leds

    too much heat with incandescent bulbs :whip:
    f-off-lawn.jpg
     
  9. Kenny*G

    Kenny*G AK Subscriber Subscriber

    Messages:
    68
    Location:
    Dickinson, Texas
    Already bought those exact wedge sockets and the 8v 250ma incandescents. The original bulbs had a blue/green tinted cover on them, what color were they from the factory ? Blue or Green ?
     
  10. Blue Shadow

    Blue Shadow I gotta get me a new title

    Messages:
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    Location:
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    Take a look at the KT-7500 images on the web and see if you find something you like. Since it was usually going to match an integrated amp that only had an on indicator lamp you could make the tuner whatever color you want with the limitation of the brightness (white color) of the bulbs you install with some color added to them. Originally, an blue green was probably correct as the meters didn't overpower brightness-wise the way high temp LED white light would.
     
  11. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,104
    Location:
    Dallas, TX
    It was a very light green tint that looks mostly yellow when lit.
    Conversion or redone examples you typically see don't look original.
    Too green
    Way too green
    Dead on
    [​IMG]
     

     

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  12. Kenny*G

    Kenny*G AK Subscriber Subscriber

    Messages:
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    Location:
    Dickinson, Texas
    Do you know where to get lamps covers that would be close to the originals in color ? I'm wanting to stay close to the original look, I'm not into the bright colored LED's.
     
  13. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
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    what i have done in the past is replace with led and leave old lamp in situ and carefully position the led to shine through the old lamp . it is trial and error but does work if patient enough . selecting the correct resistor to set the brightness is also trial and error but can see the led running at very low current so should last forever . original lamp obviously best option if available .
    i forgot adding a bridge rectifier and good practise smoothing cap too . not hard to do .
     
  14. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,104
    Location:
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    Green lamp covers. No affiliation.
     
    Last edited: Oct 16, 2018
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  15. hopjohn

    hopjohn Silver Face Subscriber

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    Alternatively you could experiment with using a green sharpie (permanent marker).
     
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  16. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
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    Location:
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    Thinking more about this I seemed to recall reading where EW recommended using 13V lamps since the KT-7500 got a little carried away with the voltage.
    Here's the thread I found where he discussed this.
    Here's a link to the bulbs he refers to.
     
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  17. Kenny*G

    Kenny*G AK Subscriber Subscriber

    Messages:
    68
    Location:
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    Thanks Again !
    I thought I had read about these using 13v lamps when I was digging for info, couldn't find it again. Just ordered some of the 13v lamps. When I was doing the voltage checks I got as high as 34.7 volts, readings in my original post.
     
  18. SicMan

    SicMan Fire up those speakers Subscriber

    Messages:
    2,974
    Location:
    Wolcott - CT. USA
    Plus too the line voltage is higher now. used to be 110 or so in the 70's and now it's 120 here in CT anyway.
    Just a step down transformer so....

    Kenny that's no load probably
     
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  19. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,113
    Location:
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    the lamps being connected will show a lower voltage across where they connect to . rb103 value decides on the current supplied to the lamps .
     
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  20. jimbo2k

    jimbo2k Adcom GFT500, 2GFA535,BandO RX2, MMC3,C101 L570's, Subscriber

    Messages:
    626
    Location:
    massachusetts
    A stained glass hobby store would have translucent green paint The more coats the darker.Used the green marker when i misplaced the paint, not even close. Deka transparent 33 light green. Made in Germany distributed by Decart Inc morrisville vt.05661 . I am sure someone else makes a similar product. This would be more a Hobby Lobby item than a Michaels 20181025_144539_Burst01[1].jpg 20181025_144539_Burst01[1].jpg 20181025_144558_Burst01[1].jpg
     

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