Kenwood KR-7600 - A few modification ideas.

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by hopjohn, Nov 16, 2017.

  1. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    I'm working through a KR-7600 and thought I would share a few modifications ideas that I implemented.

    Lamps
    Having worked on many Sansui Tuners and also the KR-9600 I've come to dislike the Stanley rubber based 8V 300mA lamps that mount on the two posts. These lamps have no base to them on their own so the only way to provide an original fit is to use some type of G3.5 globe lamp and remove the bases of those which is a PITA. If you're successful in removing the lamp you likely still have to solder on longer leads to make it work.

    Going the LED route is okay and I've been successful putting 10mm style LEDs in place of these. It's been a while so I don't recall all of the details, but the end result is always a compromise to incandescent lighting which gives you the nice warm glow you'd expect from vintage gear.

    Moving on to the solution. I decided to use #50 7.5V 220mA lamps which have E10 bases. I incorporate them by using an E10 socket with solder tabs that extend outward 180 degrees from one another. These can be found on that auction site in lots of 10. One tab has the perfect length for mounting. The other needs to be bent up and then out again for the correct spacing to slide onto the posts and be soldered on (Hint: abrade the posts first or you'll have trouble getting the solder to take). Adding some heat shrink to the base body and also the posts eliminates any potential for shorts. The height will be a bit greater once the bulb is installed compared with the originals but on the 7600 (and probably the 9600 as well) there is plenty of depth within the lamp assembly to spare so there are no issues with fit.

    [​IMG]


    Filter cap ground strap
    The 7600 has some healthy sized filter caps (12,000uF 63V) but I think the grounding strap on them is a bit wimpy. In place of the original braided strap I used a nice piece of solid core copper from some industrial Romex and soldered two ring terminals to each end. The copper strap is wound around the chassis tang and soldered up with a high wattage iron.

    Original
    [​IMG]

    Replacement
    [​IMG]

    Moving the regulators off board
    The regulators on the KR-7600 on are in close proximity to several resistors which get pretty darn hot. Qk1 is particularly vulnerable and is why it is given such a large heat-sink. Rather than try to keep those cool next to components that will always run hot, I've moved them off board underneath the PS.

    I make use of the heat-sink from the original odd-ball rectifier which I had replaced. There are three holes in the chassis rail where the PS screws down, but only 2 holes are used so adding a third hole through the PS board allows me to take advantage of that hole and mount the heat-sink. Both regulators are then isolated with mica and plastic shoulder washers. After adding some thermal compound I screw them into the existing threaded holes. I follow that up by adding some split washers, nuts, and thread lock to the back to make sure they stay in place. Using some hook-up wire I route the appropriate BCE connections to the board and tidy it up with some heat-shrink insulation.

    [​IMG]
     
    Last edited: Nov 16, 2017
    kydog, Goldie99, audioman00 and 4 others like this.

     

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  2. mbz

    mbz AK Subscriber Subscriber

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    Nice input, thanks. Nice work also.

    I understand that grounding is a complicate issue and that there is a school of thought that a star point connection to the chassis
    is the preferred method and that the star point should not coincide with the GND point between filter caps. Tryimg to understand, but
    as we are talking about "short circuit" connections not sure how it's better. Also, maybe something for you to consider in next project.
     
  3. mbz

    mbz AK Subscriber Subscriber

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    On second thoughts, the two back black wires are not directly connected to the bar between the main caps, so it's ok?
     
  4. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Ideally you'd want to have all the ground points be at a single location here, but one tang isn't going to be enough to handle all the wires so that becomes impractical. Their close proximity though should do well enough I'd think.
     
  5. tinkerer

    tinkerer AK Subscriber Subscriber

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    hopjohn those are some great mods, really appreciate the post.
    Question regarding the power supply mod: It appears you used a MJE15032G for the Qk1 2SC1419 transistor. What did you use for the Qk5 2SA885 transistor?
    Thanks again. Jim
     
  6. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Thanks Jim!
    Yes, you're correct for Qk1 I used a MJE15032G. For the PNP Qk5 I used a MJE15033G.
     

     

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  7. tinkerer

    tinkerer AK Subscriber Subscriber

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    Thanks hopjohn appreciate it.

    I need some assistance with diodes on the X00-1770-10 Power Supply Board "A" but I will start a new thread "KR-7600 Power Supply Diodes"
     
  8. gort69

    gort69 AK Subscriber Subscriber

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  9. tinkerer

    tinkerer AK Subscriber Subscriber

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    Thanks gort69. The SM evidently is correct. Appears that at least one of the diodes have been changed on my board, since Dk1, Dk3 do not match appearance wise.
     

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