Weird TSL100 bias problem

Discussion in 'The Workbench' started by Parkerx02, Dec 7, 2019.

  1. mcblink

    mcblink Well-Known Member

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    Is it just me or has there been a recent surge of TSL threads lately?
     
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  2. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    have you tested R8 & R9?

    unplugged/power off, put your tester on each side of the resister & test for ohms...
     
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  3. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    But it's not steady.
    The insulation between pin 4 and pin 5 needs to be infinity.
    If there is 500K - 700K then high voltage is bleeding into the bias circuit.
     
  4. Parkerx02

    Parkerx02 New Member

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    Just watched a video where a guy cut the board away from around pin 5 at each tube then lifted a leg off r7, r10,l r66, r70 and ran the lifted legs to pin 5 of each of the power tube sockets. What do you think? Also, when I ohm pin 5 to pin 5, I get 11.2, which is correct. Why is the value correct with the board being bad? Thanks so much!!!
     
  5. Parkerx02

    Parkerx02 New Member

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    Between pins 4 and 5 is .500m-.700m, not 500-700k. Still, should be OL, I get it and much appreciate it
     
  6. Parkerx02

    Parkerx02 New Member

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    So... R r9 is 1 ohm like it should be, r8 is 50 ohm although the schematic says it should be 100 ohm... but... r6 read 2.1m yet should read 1 ohm, and r6 has a black burn spot on the bottom side. Fn eureka! When I got the amp, it had 2 stock tubes, and 2 eh, so someone had a prob at one time. Im going to replace r6 tomorrow and reevaluate!
     
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  7. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    .500m "is" 500K
     
  8. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    If you don't fix the board first, everything you are doing is a waste.
    It's going to fail again.

    There is not even 1 Meg resistance between screen and grid that's not very good.
     
    Last edited: Dec 8, 2019
  9. Parkerx02

    Parkerx02 New Member

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    I replaced r6 today then biased to 70mv, which is 36ma on my in socket bias probe. Have been playing for an hour and sounds great, not hiss, pops, crackles, nodda, and the bias stayed put the whole hour. I then ohm'd between pins 4 and 5 again and still not ol, but you would never know there was a prob since its behaving so good, which trips me out. Now, between pins 4 and 5 ohms start at 200k, go up and up, after 300k, goes ol for a second, then goes to .900m and counts down, down, down to about .600m. So weird. I tried ordering the bias drift correction board, but their site is jacked so I emailed them. Seems the bias boards are obsolete. I want to put full size pots on the top side, by the tubes, but that is another day. What exactly is a normal reading ohming between pins 4 and 5?
     
  10. mcblink

    mcblink Well-Known Member

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  11. Parkerx02

    Parkerx02 New Member

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  12. mcblink

    mcblink Well-Known Member

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    Just sayin' man. Best of luck!
     
  13. Adieu

    Adieu Well-Known Member

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    Wait, m mili (1/1000) or M mega (10^6)?
     
  14. Parkerx02

    Parkerx02 New Member

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    Mega, sorry. I tried another dvom, and had same results. All tubes sockets are identical at pins 4 and 5, starts off at 200k, then goes up up up to 900k, then back down down down to 600k. I did the exact same test on my jcm dsl100 and had the exact same results, same numbers, to the T. They are both jacked identically? They both sound great and don't have bias drift. So nuts. If I would have never measured pins 4 and 5, Id have no idea anything was up. What are the odds? I don't have bias drift in either head, yet both ohm identically between pins 4 and 5?
     
  15. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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  16. Parkerx02

    Parkerx02 New Member

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    Yours is all good now DoD? Mine is acting great and bias is super steady. Just trips me out why my meter doesn't go to OL when measuring pins 4 and 5, and why my DSL measures the exact same. Counts up, then counts back down. Sounds killer though. Have it now going through an old Carvin cab with an xpattern of v30's and t75's. Red channel, gain on 5 with an sd-1 in front. Its pretty close to Accept's Balls to the Wall tone.
     
  17. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    yep, seems to be...
     
  18. Parkerx02

    Parkerx02 New Member

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    So, I'm looking at the schematics n can't see how there would b no continuity/ol between pins 4 and 5. From v5 for example, pin 5 goes through r7, then r4, then c6, then r3, then r63, then r60, then ends at pin 4 in v5. That's 773k total resistance not including however much resistance c6 has. Am i wrong in thinking this way?
     
  19. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    The board is not bad.

    The resistance between power tube sockets pins #4 and #5 should be about .5M so that is correct.

    The problem was described in @Parkerx02 post #4 quoted above. Most likely the 1 ohm bias monitoring resistor is bad. The cathode circuit is measuring 5.6M resistance. The power tubes are OFF and will not operate with that resistance.

    @Dogs of Doom mentioned it and his post was overlooked.
     
  20. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Yeah, he got it. R6 was bad. That is the left side bias monitoring resistor.
    They always go out.
    You should change both of them, R6 and R9.
     
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