Developing the BOM for a KR-6160 restoration

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by dlucy, Mar 6, 2017.

  1. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Yorktown, VA
    I've finally pulled the first KR-6160 out of the "to do" stack and started the restoration. I'll share some of what's going on here and ask for some help along the way. After it's done and working, I'll post the results and the BOM for a recap as well as a more-thorough restoration.

    This unit sounds pretty great as it is, but it started acting flaky and I took it off the shelf for later restoration. That time has arrived.

    IMG_1278.JPG IMG_1296.JPG IMG_1317.JPG
  2. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Yorktown, VA
    There are some oddball parts in there already. This should be fun....

    IMG_1354.JPG IMG_1355.JPG IMG_1359.JPG
  3. roger2

    roger2 . Subscriber

    Weird parts, nice pics :)

    I don't recall seeing any green colored resistors in Kenwood units. Are those fusibles?
  4. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Yorktown, VA
    I'm not seeing references to fusible resistors or lower-than-1/4-watt ones, so I don't think they are fusible. I'd love to have someone more-experienced confirm or correct this, though.
  5. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Yorktown, VA
    I'll start off with the MAIN amp board:

    MAIN-SCHEMATIC.png MAIN-UA1384J-IMG_1337_edit_tiny.png

    The transistors first:

    The schematic lists Qe1-Qe4 as 2SC693U(E or F), but this unit has 2SC458 :eek: transistors installed in those locations, so I'll put in KSC1845F.

    Qe5,Qe6 are listed as 2SC627 in the schematic, but I can't read the label on these. The datasheet for 2SC627 is typical and boring until you reach the hFE of "360 minimum".

    2SC627 NPN CBO=200 CEO=200 IC=100mA Pd=700mW fT=20MHz hFE=360

    So, these will have to be high output and it took a thorough run through alltransistors to find devices that matched and Mouser to find one that was available and matched or exceeded. I'm going to try ZTX696B instead of a Darlington since I really don'[t know enough about them to select and replace them confidently.​

    Qe7,Qe8 are listed on the schematic as 2SC960(I, L or M) and my unit has 2SC484Y installed there. These are complemented by the 2SA484Y in Qe9,Qe10, so a little extra care for this replacement.

    2SC484Y TO-39 NPN CBO=150 CEO=110 Ueb=5V IC=1.5A Pd=800mW fT=10MHz hFE=30

    KSC2073 will handle those needs well and it has a complement of KSA940, so KSC2073/KSA940 will be the ones for these.​

    As stated above, Qe9,Qe10 is marked as 2SA607 on the schematic, but my unit has 2SA484Y in those positions. As stated above KSC2073/KSA940 is a complemetary pair that matches these parameters, so KSA940 is what I'll use for Qe9,Qe10.

    Qe11 has a 2SC373 on the schematic, but a 2SC984 on the actual board.

    2SC984 TO-1 NPN CEO=50 CBO=50 IC=500mA Pd=350mW fT=100MHz hFE=30/300

    Either KSC2690A or KSC2383 should work fine in the Qe11 position.​

    The strange gold-legged black-capped transistors at Qe12,Qe13 are 2SC715E

    2SC715E TO-92 NPN CBO=40 Ved=5V IC=200mA Pd=125mW fT=100MHz hFE=80


    It looks like KSC2383O will do fine here.​

    Lastly, Qe14 is a 2SC734Y

    2SC734Y TO-92 NPN CBO=70 CEO=50 Ueb=5V IC=150mA Pd=300mW fT=75MHz hFE=120

    And I think KSC2383O will do fine here, too.​

    There are only two sets of diodes actually on the board, so they are easy:

    De1,De2 are 1N60 Germanium diodes, so I'll replace them with NOS 1N60 or 1N60P diodes

    1N60 Germanium glass diode Vrrm=40V If=30mA Ifsm=150mA​

    De3-De5 are strange-looking twinkie-shaped devices that the schematic calls out as SM-150-S. I couldn't find specs exactly for the SM-150-S, but I found several places where SM-150-xx were discussed and it appears these are simple 100 V 1A diodes. If anyone knows differently, please let me know. If that is correct, then they can be replaced with 1N4002, but I like the ultra fast soft recovery UF4002 better.


    The capacitors are almost all electrolytics, so the replacements are mostly easy: bump up the voltage so the replacements are operating at 60-70% rated voltage, use nothing lower than 35 V (where possible), use film caps (for zero leakage) where possible (4.7 uF or lower) or low-leakage caps (Nichicon KL series) for everything else.

    • Ce1,Ce2 1 uF 50 V --> UKL2A010KDD 1 uF 100 V (Mouser doesn't even stock the 50 V version anymore) or ECQ-E1105KF3 (much larger film cap, but it has no leakage, this one is the smallest I can find, and it will fit... it'll just be ugly)
    • Ce10,Ce29 47 uF 3.15 V --> UKL1V470KPDANA 47 uF 35 V
    • Ce11,Ce12 100 uF 50 V--> UKL2A101KHD 100 uF 100 V
    • Ce13 220 uF 25 V--> UKL1V221KPD 220 uF 35 V
    • Ce15 47 uF 100 V Axial --> TVX2C470MCD 47 uF 160 V Axial
    • Ce3,Ce4,Ce14 100 uF 3.15 V --> UKL1V101MPDANA 100 uF 35 V
    • Ce5,Ce6 33 uF 16 V --> UKL1E330MEDANA 33 uF 25 V

    I'm crazy, so I'll be replacing the one ceramic cap while I'm in there

    • Ce7,Ce8 220 pF --> FK28C0G2E221J 220 pF 250 V C0G (NP0)

    I'll probably replace all the resistors on this board with metal film ones, but I don't want a bunch of "hey, why would you do that" comments just because I'm OCD and have lots of spares from mistaken orders, so I'll just skip putting those in here.

    There are two trimpots on this board, so I'll replace them instead of rolling the dice and having them blow a transistor or more:

    VRe1,VRe2 are three-legged, single-turn 10K trimpots so they'll be replaced with 3309W-1-103

    This board leads directly to the output transistors and their resistors on the heatsink, so I'll cover those while I'm at it:

    The output transistors Q1-Q4 are marked as 2SC1115 on the schematic, but 2SC898 are installed instead.

    2SC1115 TO-3 NPN CBO=140 CEO=80 Ueb=5V IC=10A Pd=100W fT=10MHz hFE=30-150

    MJ21194G will be a fine replacement for these output transistors.​

    Power resistors at R171,R172,R271,R272 and R173,R273 may have been stressed, so they'll get updates, too.
    • R171,R172,R271,R272 0.47 R 2-3 W --> CPF3R47000JNB14 0.47 R 3 W 5%
    • R173,R273 4.7 R 2-3 W --> CPF34R7000FKB14 4.7 R 3 W 5%
    The output in the KR-6160 is cap-coupled, so C171,C271 are huge terminal-lead caps installed up top, but I'll cover them here.

    C171,C271 output-coupling caps handle the amplified signal just before it goes to the speakers, so these will need to be big (to avoid low end rolloff) and great quality (low or no leakage). Sadly, the KL series doesn't cover this much capacitance at this voltage (need 63 V minimum), so I have to look elsewhere. Nichicon makes plenty of snap-in and leaded caps in this size, so I'll choose some options that claim better audio performance but are roughly the same price as non-marketing-crap ones.

    C171,C271 2200 uF 63 V --> UKW2A222MRD or LKG1K222MESAAK 2200 uF 100 V

    (If Nichicon made ones that had skull tattoos on the side or little glasses of Japanese bourbon, I'd put those in there instead since they'd be "better audio quality" ;))​

    Ok, so what of the above is just dead-wrong?
  6. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

    Calgary, Alberta
    This is awesome! Very nice details and pics!
  7. rcs16

    rcs16 Super Member

    Baldwin, Ontario, Canada
    Hello Doug,

    I do not know how much experience that you have doing this sort of work, but my suggestion is to first figure out what is causing the flaky behavior before changing all these parts. Just the way that I troubleshoot my stuff and what I see other experts doing. I have seen far too often folks taking your approach with good intentions, just burying them selves alive and end up with a basket case.
    Start to figure out if the issue is in one of the channels or both, that way you can determine if it is a common source like a power supply issue.
    Determine if it is tarnished switch contacts, dirty pots etc first before you start changing comps.
    If you are going to heed my advise at least change the ecaps first before changing out semi's.
    Does not hurt to review threads about this unit to determine what has failed and what was done to fix them.
    I see quiet a few hermetically sealed bjts, they may out last you and me and the new ones you put for replacement.
    I would not call them odd ball parts, just the way that they made them back in the early 70's. Many of those bjts were hand assembled before automated packaging came in the late 70's. Who cares what colour the laquer is on the resistors, every mfg has their own processes, has nothing to do if the comp is work properly or not.
    The amp is a fairly simple design, single supply, bootstrapped VAS, quasi-complementary, ecap coupled to load.
    Do you have any instrumentation, like a signal gen, scope, DMM? If so use them to measure the performance of each section of the receiver.

    Good Luck
    Last edited: Mar 11, 2017
    dlucy likes this.
  8. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Yorktown, VA

    Thanks, that's really good advice. You guys here on AK have been a big help troubleshooting issues and getting me through to the right answers.

    This particular thread is a "build the big list of parts and modern replacements" so the next person with a KR-6160 has a better start. I've got two 6160's, one of which is working fine and the other is just flaky, so I'm taking this opportunity to tear one of them down completely, build up the list of actual components (not just what the schematic says), compile some photos of the boards and notated pinouts, and put it all back together.

    I'll definitely change out all the electrolytics caps as they are far past their life expectancy and I won't allow them to fail and take out anything more expensive. It'll also sound better when I'm done, as I know from all the other vintage receivers I've done so far. The known-noisy transistors (e.g. 2SC458) will get replaced, as will any power resistors near the output transistors.

    Your points about troubleshooting and reading other threads before replacing are good and solid. Again, thank you!

  9. Bassblaster

    Bassblaster Super Member

    Cambridge, Ohio
  10. grhinson

    grhinson New Member

    This might be as bit late coming to you, but I am in the middle of repairing a few of these KR-6160s and they all seem to have the same problem of failing driver transistors. I have the service manual and within it gives a service bulletin suggesting to replace Q1-Q4
  11. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Yorktown, VA
    You're not late at all. I made the mistake of starting several restores at once and I haven't moved forward (much) on the KR-6160.

    Youre talking about the 2SC693's on the main amp board? My plans are to replace them with KSC1845's. But I'm approaching this with a replace-most perspective.

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