Harman/Kardon A500 Tube Amp

Discussion in 'Tube Audio' started by tube-a-lou, Jul 1, 2011.

  1. tube-a-lou

    tube-a-lou Super Member

    Messages:
    3,715
    Hi all,

    Went shopping today and someone had a Harman/Kardon A500
    Tube amp, needs to be redone and the gentlemen said he'll sell it me
    for $250.00, good deal, I always redo these tube's amps anyway so
    what do you think??:scratch2:

    Tube
     
  2. wildone

    wildone Learning as I go!

    Messages:
    721
    Location:
    The Great NorthWest
    Well I have one, and will be using it as my bench amp. I have the matching tuner too. My A500 has the HK tubes still. I have not done anything with it yet, They say they are nice amps. Like 25w per ch.

    Pics?

    WO
     
  3. tube-a-lou

    tube-a-lou Super Member

    Messages:
    3,715
    Hi,
    No pics yet, haven't brought it home, looks to be in good shape, look underneath
    it has those huge Sprague black beauty caps on it. the guy told me when he put it
    on, one of the can caps started to smoke, so I guess that needs to be replaced and
    all the rest!

    Tube
     
  4. GordonW

    GordonW Speakerfixer Subscriber

    Messages:
    17,057
    Location:
    Marietta/Moultrie GA USA
    They're really good, once they've been recapped.

    I replaced every coupling cap, and every electrolytic cap (including the cans) on the last one I had on the bench. Total of 24 caps. Be sure and don't forget the little electrolytics in the preamp/phono stage!

    It sounded magnificent afterward.

    Regards,
    Gordon.
     
  5. Wardsweb

    Wardsweb Behind The Curtain Staff Member Admin

    Messages:
    7,114
    Location:
    San Antonio, Texas
    These really are sweet amps once they have been recapped. Here is mine I used for years before giving it to Kamakiri.

    [​IMG]


    Cap job
    [​IMG]

    More pics and the matching tuner here:
    http://wardsweb.org/misc/HK_A500.jpg
     
  6. buickguy62

    buickguy62 Active Member

    Messages:
    168
    I've restored a number of these with input from Jim McShane. I replace at a minimum all the electrolytic and coupling caps, the balance pots and the diodes, and liberal use of De-Oxit. I have an Excel spreadsheet that lists the components and sources I use --it's a good place to start--you might have your own preference on component selection. PM me for the spreadsheet if interested, I also have the schematic if you need one. One trick I've found is to use two of the dual 50/50 ufd. 500V JJ can caps from tubesandmore (to replace C29 A&B, and C30 A&B). They are under $10 each (plus the clamps), they fit in the existing holes and allow plenty of room underneath for the additional caps-see pics--that area gets crowded if you put all of the replacement caps under the chassis. See pics.
    Tom
     

    Attached Files:

  7. tube-a-lou

    tube-a-lou Super Member

    Messages:
    3,715
    Hi all,
    Thanks for all the info, I'm really thinking of getting it maybe I'll try to get
    him down a little, how about the power tubes 7355 is there replacements,
    would 6V6's be good or 7591, I've read that with a little mod you can use
    6L6's??

    Tube
     
  8. Patrice B

    Patrice B AK Subscriber Subscriber

    Messages:
    1,716
    Location:
    Montréal, Canada
    7591XYZ are known to be a good (and cheap) replacement. Some mods have to be done however to allow it.
     
  9. tube-a-lou

    tube-a-lou Super Member

    Messages:
    3,715
    Hi,
    Decided not to buy it, I'm going to stick with the Fisher. besides he would not
    go down in price, it's odd the knobs are off, the front panel is off, the bottom panel
    is off and the light button the the switch is missing, so that's it thanks for all the help
    and I'll wait for a better one to appear.

    Tube

    Tube
     
  10. GordonW

    GordonW Speakerfixer Subscriber

    Messages:
    17,057
    Location:
    Marietta/Moultrie GA USA
    Actually, the only mod that is needed, is to snip off the one pin (from the base of the tube itself) that the 7591 (and 7591XYZ) uses, that the 7355 does not. IIRC, that's pin 4. Check with a good tube manual... it'll be the pin that's also connected to the screen grid, in parallel with the "normal" pin that's used for screen in the 7355. You only need one screen grid connection... so that one that's in the unused position on the 7355, can go away safely.

    Regards,
    Gordon.
     

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