I give up!

Discussion in 'Tube Audio' started by tube-a-lou, Sep 6, 2017.

  1. tube-a-lou

    tube-a-lou Super Member

    Messages:
    4,420
    Hi all,
    I have a Hickok 600A tube tester and after it's on for a least 45 minutes every tube
    I test it show's a short. When I test it after I turn it on and after 15 minutes it fine, something
    happens to it when it get hot. I did replace all the bulb's and a few resistors so maybe something
    goes out of wack when it heats up, I'm at a loss do you guy's have any ideas?

    Thanks
     

     

    Please register to disable this ad.

  2. arts

    arts Super Member

    Messages:
    3,239
    Location:
    Qc, Canada
    Everything involved with the short test is suspect.In particular R10,R15,R23 & C1.
     
    Retrovert likes this.
  3. tube-a-lou

    tube-a-lou Super Member

    Messages:
    4,420
    Thank you I'll check those resistors out.
     
  4. arts

    arts Super Member

    Messages:
    3,239
    Location:
    Qc, Canada
    To me,it seems that something is seriously drifting with heat. Either the resistor values or perhaps the cap is breaking down. I wouldn't waste time trying to test them,just replace all of the ones I listed.

    Also,although rare,sometimes the striking voltage of neon bulbs declines with age and temperature level. Grasping at straws,but it happens;)
     
    Retrovert and drtool like this.
  5. KKnight

    KKnight Active Member

    Messages:
    336
    Man.. if you use that 600A regularly, rebuild and re-calibrate it! Like Arts said, look at those old crumbly resistors and worthless capacitors and replace them. There is a lot of good recent posts on AK on the state of decent metal film and other resistors now, and what decent electrolytics to use.
     
  6. arts

    arts Super Member

    Messages:
    3,239
    Location:
    Qc, Canada
    Any luck?
     
    Dandy likes this.

     

    Please register to disable this ad.

  7. tube-a-lou

    tube-a-lou Super Member

    Messages:
    4,420
    Hi Arts, I've been working so I'll open her up this weekend and see.
     
  8. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    30,741
    Location:
    Central Missouri
    I immediately wondered if there was a cap involved since you said you replaced only resistors. As arts posted, find C1. It's 99% likely to be an old paper foil wax capacitor and needs to go if it hasn't already.
     
    Bill Ferris likes this.
  9. tube-a-lou

    tube-a-lou Super Member

    Messages:
    4,420
    I replaced all the caps by the short switch and light, I think it was a .01uf
     
  10. arts

    arts Super Member

    Messages:
    3,239
    Location:
    Qc, Canada
    And????
     
  11. tube-a-lou

    tube-a-lou Super Member

    Messages:
    4,420
    That was awhile ago when I first went though the tester. Sorry working on my new Gibson
    guitar amp. I let you know when I open the tester up again.
     

     

    Please register to disable this ad.

  12. tube-a-lou

    tube-a-lou Super Member

    Messages:
    4,420
    Went into the tester this weekend, I first replaced the 200ohm reostat I picked up a newer style
    (slightly used) and had it on for about 1/2 hour with no trouble I also took note that the chassis
    above the reostat doesn't get as hot as it did before it just seems just warm, last time it was much
    hotter, I'm still going to replace a few resistors as I go on with it.
     
  13. ferninando

    ferninando Lunatic Member

    Messages:
    12,453
    Location:
    San Jose Ca.
    tube a lou, do replace all possible caps as well if you have not done so.
    I have a 600a and have not had any trouble yet. I have replaced some Rs and Cs.
    I should look into the 200ohm reo and see if it gets hot like yours did.

    edit:
    the 200ohm reo is the line adjust R. were you able to adjust the line V with it.?
     
    Last edited: Sep 17, 2017
  14. tube-a-lou

    tube-a-lou Super Member

    Messages:
    4,420
    Hi Ferninando, yes I was able to do the line voltage with it, I don't know if I have to adjust anything
    inside yet but so far it's good. The new one is lot smaller and seems better made than the old one
    the coil is a lot neater, I don't know if that makes it more efficient but it might help, plus the original
    is about 50 plus years old. I'm going to do some more tube test's today.
     
  15. thornev

    thornev Active Member

    Messages:
    290
    Location:
    Mid Hudson Valley, NY
    Hi All. I just invested in a Hickok 600A. It seemed very broken (could not get LINE ADJUST to adjust) so I started by replacing the 83 and 5Y3GT. That fixed that problem. Now I have the same problem as the OP so I will now replace the afore-mentioned parts. Is there any place in this forum where a complete restoration of a 600A is documented? Thanks, Thorne
     
  16. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    30,741
    Location:
    Central Missouri
    thornev likes this.

     

    Please register to disable this ad.

  17. thornev

    thornev Active Member

    Messages:
    290
    Location:
    Mid Hudson Valley, NY
    Yes I have all possible documentation, even different versions. I'm not very good at mapping a schematic to the chassis parts. I try measuring (using a DMM) parts and finding them on the schematic, but because parts are sometimes out of tolerance, or are in parallel circuits, I end up with too many question marks. I just got done trying to map resistors (yes, the caps were fairly easy), and there are 9 resistors I couldn't even find in the chassis. I am going to replace anything out of tolerance and all caps as long as I can get to them.

    For example, there are 2 versions of schematics, 782W and 830W. I was trying to map to 830W figuring the latest must be the right one and after a few hours, I realized the reason parts weren't mapping was that it is actually the 782W version that maps to my chassis. Apparently I have an older 600A. But still there are 9 resistors I cannot find on the chassis. The 782W version doesn't even display the BIAS FUSE.
     
    Last edited: May 14, 2018
  18. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    30,741
    Location:
    Central Missouri
    If the resistors are readable you can always ignore the schematic, get the values of the resistors themselves, and go from there.

    I've recapped a couple of tube testers but I dread checking and replacing resistors in a Hickok. I know it has to be done though.
     
    thornev likes this.
  19. thornev

    thornev Active Member

    Messages:
    290
    Location:
    Mid Hudson Valley, NY
    Thanks, tox. Yeah, it's hard getting to some parts in the 600A. I did try reading the color bars, but some don't match to the schematic parts list on the schematics which surprised me. I suppose it's possible that I have a transition model for which a schematic was never made public or just isn't available anywhere. I have read that Hickok was known for always changing designs. I'm not in the business of testing tubes - I have a lot of tubes because I was doing tube rolling with a Little Dot III headphone amp and now that I'm into restoring tube devices, I have a Fisher 500-C with its glorious tubes. A tube guitar amp is up next !
     
  20. tube-a-lou

    tube-a-lou Super Member

    Messages:
    4,420
    Hi thornev, I'm the original poster and I to have problems with it, after the tester was on for at least
    45 minute every tube would show a short, then I got annoyed one day and started switching the short
    control back and forth and after that it stopped, could be age, dirt or bad resistor still want to change
    them all but some sizes are to find, but so far since that work out it's been good.
     
    thornev likes this.

Share This Page