SHERWOOD S2000 Tuner 6X4 Tube Red Plating?

Discussion in 'Tube Audio' started by Grid, Jan 14, 2018.

  1. Grid

    Grid AK Subscriber Subscriber

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    I recently bought an S2000 cheap just for the cover. Seller said the tuner was not powering on. But it is working! In shipment, the 6X4 tube came loose and broke. I got another in there. FM sounds fine and so does AM. However, on AM at certain segments of the band, I hear a "motor boating" kind of distortion. The 6X4 glows inordinately brightly. So I'm wondering if I should change the capacitors and those 470 ohm 10 watt resistors. Haven't yet checked voltages on that tube.

    I should mention, I'm a mere novice at this.

    s2000sch1.jpg s2000sch2.jpg
     

     

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  2. s-petersen

    s-petersen Scott Subscriber

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    The resistors may be ok, but the electrolytic caps should be changed, ...strange the schematic says 6X5GT for the rectifier
     
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  3. Grid

    Grid AK Subscriber Subscriber

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    Yeah, I was wondering about that. I understand, electrically they are the same? But the 6X4 is a mini. I gotta get in there and see if there are those 470 ohm 10 W resistors and if there are those 40 40 40 340V electrolytic caps. I mean, would a 6X4 require that those resistors and caps be rated differently?
     
  4. s-petersen

    s-petersen Scott Subscriber

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    The ratings of the caps and resistors should be the same, I am not familiar with the 6X5gt rectifier
    Edit:
    I looked it up, and they are similar in power handling capability
     
    Last edited: Jan 14, 2018
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  5. Grid

    Grid AK Subscriber Subscriber

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    OK, thanks. I did learn that there were several builds of this tuner. I think the 6X5GT was used in "build 1."
     
  6. Dave451

    Dave451 AK Subscriber Subscriber

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    Couple thoughts: the 6X4 is a very bright little tube. I have a Scott tuner with one and the filament really lights up. The plates shouldn't light up, of course (turn red or orange), if that's what you're seeing. As for the AM noise, the band is subject to increasing sources of interference, particularly from things like sub-standard LED lamp switching power supplies, plasma TV's, compact fluorescent bulbs and the like. What you're hearing may be RFI (Radio Frequency Interference). I just finished restoring a Fisher 1800 and I can barely use AM in my house because of this. Good luck with the 2000!
     
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  7. radioeng

    radioeng Reformed speaker builder

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    If the rectifier plates are glowing red, stop using it at once! This is a sure sign that the filter capacitor is shot. If you do not wish to be gouged on the price of a multi section cap. Make your own. An octal female socket will usually fit into the hole that an FP style cap once occupied. All you need is a male octal socket and the correct value of radial electrolytics (see picture). This also makes future service very easy. You just pop out the socket, and change out the offending cap!
     

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    Last edited: Jan 15, 2018
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  8. Dave451

    Dave451 AK Subscriber Subscriber

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    radioeng,
    Interesting fix on the electrolytic caps. Haven't seen that one before.
     
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  9. gadget73

    gadget73 junk junkie Subscriber

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    They actually did make some octal plug-in can caps for military and ham gear. Honestly never thought about re-capping hifi gear that way but I kinda like it.

    Sherwood was pretty terrible about running production changes and schematics that don't match. Maybe 50 years ago you could get all of the appropriate docs if you were a factory Sherwood repair shop but these days the info just isn't all there. Match your replacement parts to what is currently in the unit if it appears to be original. It worked with those value parts when it left the factory and it will work again with them.
     
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  10. knockbill

    knockbill Addicted Member

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    I got a boxful of those octal base lytics,,, thought about recapping them, but if I'm going to recap something, it may as well match the amp,,, hate to do the same amp twice!!!
     
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  11. Grid

    Grid AK Subscriber Subscriber

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    That is so cool and clever. Quite original. Very tempted! Thanks. I'll have to look again to verify if the plates themselves are lighting up--it just may be the 6X4 is a bright tube.
     
  12. Grid

    Grid AK Subscriber Subscriber

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    Especially with amps where no cage is used. I like keeping the original look.
     
  13. Grid

    Grid AK Subscriber Subscriber

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    Yep, good common sense, gadget, thanks. Look at all the builds for the S5000. Recently I found it next to impossible to find schematics for the S5000II, the build that uses the 7591 output tubes.
     
    Last edited: Jan 14, 2018
  14. Grid

    Grid AK Subscriber Subscriber

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    I will have to take another look when I check voltages to see if in fact the plates themselves are glowing. Thanks very much. I use a long wire antenna extended out my 8th floor window; get great local and DX AM. This noise is definitely the tuner. In fact the motor boating squeals at times (but not as in microphonics).
     
  15. Dave451

    Dave451 AK Subscriber Subscriber

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    I read a description of a 6X4 somewhere as a "Fire Bottle." Pretty apt!
     
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  16. Grid

    Grid AK Subscriber Subscriber

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    And I've heard it described as a transformer killer. I had the tuner running a good 20 minutes. I think if it was red plating, disaster would have happened within 20 minutes. I think.

    I ordered those electrolytic capacitors. Meantime, will look at voltages.
     
  17. Grid

    Grid AK Subscriber Subscriber

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    Update. Appreciate everyone's take on this: Checked voltages on the 6X4. They are, like, 100 volts less than the schematic says. Checked those 470 ohm 10 W resistors (one end disconnected). One is 500 ohms, the other 510 ohm. I have no parts list showing tolerance percentage, but would those be still within spec? I have ordered the electrolytic capacitors.

    Thanks!
     

     

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  18. LexDM3

    LexDM3 AK Subscriber Subscriber

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    I have a Sherwood 2000 tuner in working order so let me know if you need voltage readings.
     
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  19. s-petersen

    s-petersen Scott Subscriber

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    Usually 10% is tolerance, so still in spec
     
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  20. Grid

    Grid AK Subscriber Subscriber

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    Thanks a million! I gotta learn my math!
     

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