"Normal" temperature for power tubes?

Discussion in 'Fisher' started by thornev, Dec 23, 2018.

  1. thornev

    thornev Well-Known Member

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    Thanks, Dave, it's not the 10ohm resistor nor the 100ohm resistor. But I did notice the brown-red-red resistor connected to pin 1 of V10 is loose. Still touching but needs resoldering.

    Off topic, I noticed that while removing the chassis bottom, I was testing for continuity on the speaker posts. What surprised me is that both the common (-) and positive (+) speaker posts have continuity when the SELECTOR on the front of the 500-C is selecting those speaker posts. For example, if the SELECTOR switch selects SPEAKER 1, the posts on the back of the unit for both + and - SPEAKER 1 posts have continuity. That means that both + and - are connected to ground which is unconventional and I thought a short circuit. The posts for the other speakers (SPEAKER 2) do NOT have continuity in this example which is what I would expect if I had selected SPEAKER 2. Can anyone explain this phenomenon?
     
    Last edited: Dec 29, 2018

     

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  2. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    In the 500C, the 4Ω tap is grounded, with the entire secondary winding (from Com to 16Ω) barely measuring over 1Ω in total. If you casually check the resistance or continuity from either the speaker Com or positive posts then of the selected speaker (as determined by the setting of the front panel switch), it will appear as if both terminals are shorted to ground. In reality, both actually will measure about 0.6 and 0.3 Ohms respectively, plus whatever resistance there is in the wiring to and through the speaker switch inside the unit.

    Dave
     
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  3. grindfix

    grindfix Full time hobby Subscriber

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    https://www.mouser.com/ProductDetail/530-105-0803-1
     
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  4. Bill Ferris

    Bill Ferris Super Member

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    Those copper caps from Weber have failed on one of my friend`s recently purchased pair of wired Bob Latino VTA M-125 CCS while playing his music on Hartsfield speakers at moderate SPL levels, and after I loaned him a straight SS (no internal dropping resistor plug in Yellow Jacket units, and I installed a CL90 in his 120 volt primary of one of the two, so he could compare between the two types of plug in SS rectification, between the 2 purchased, and identical amps, after about a week of comparing, he went with the Yellow Jacket plug in type and hasn`t looked back..

    Yes, I know, subjective tastes !!

    Granted, he is a good bass player, and likes the bottom end of "sound reproducing tube amplifiers" to have the straight SS tightness in the lower octaves..
    Just saying..
     
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  5. sKiZo

    sKiZo Hates received: 8642 Subscriber

    Yup ... whatever works for you is what works best. There's some that say a rectifier can't possibly make any difference in the sound, but I'm not in that camp. I swear by the Mullard GZ37 I've been using here, and have the copper cap strictly as a backup.

    PS - if you DO run a tube rectifier, I strongly suggest the "yellow sheet" mod on the rectifier socket. Just a couple diodes using unused pins on the socket for mounts, eliminating any chance of reverse current killing the tube. And a thermistor on the hot AC in is pretty much a no brainer as long as your B+ stays in the recommended range. The mod will work with any 5AR4 or electronically equivalent rectifier.

    [​IMG]
     
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  6. Bill Ferris

    Bill Ferris Super Member

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    I`m aware of the SS protector diode mode, but it`s not necessary for the countless permanent tube rectifier removals that I`ve done over the past 43 + years, to my customer`s, friends, and myself`s sonic satisfaction, be it music creation, or music reproduction tube amplification !!
    After all, their paying the bill, and will/can complain, if the sound is not to their liking, while listening to their gear, whether playing an amplifier, or their favorite track is played through their modified(tubeless rectification, at home, or though my test speakers, straight though DQ- 10`s in my sunroom)

    Please, feel free to use whatever method of rectification you find pleasing to your ear..

    I`m not on this planet to convince you what sounds good to your ears !
    I, after many decades of being in this business, found that, often tube rectification`s effects, are over blown, for various reasons, without really listening to the effects of It`s voltage drop sponge in reproduced sound, that wasn`t really present when recorded on usually responsively tight playback systems, when being recorded, and mixed down.

    But ,if that`s music playback`s effect is desired, so be it, just not in my, and many other`s world, once the difference is tasted..
     

     

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  7. sKiZo

    sKiZo Hates received: 8642 Subscriber

    Most important consideration ... the GZ37 is much prettier than the copper cap! Even stands tall amongst the KT120's it does ... <G>

    [​IMG]
     
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  8. trainbuftony

    trainbuftony Electron Herder Subscriber

    As far as temp is concerned, the data sheet usually gives solid advice. Havent seen it posted here yet, but most manufacturers spec 200°as maximum bulb temp. These are of course scientists so it goes without saying they are using the metric system. Max bulb temp on nearly every consumer tube which ive read the sheet for says 200 celcius. Surprised that this figure is so hard to come by. Its in every data sheet for every tube we use, like 6.3v heaters, its something i committed to memory
     
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  9. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    And for those of us who try and NOT use the Metric system or Celcius/Kelvin 200*C equals roughly 392*F. (Damned Colonials! And PROUD of it!)
     
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  10. Pio1980

    Pio1980 AK Member Subscriber

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    Iirc, C/F = C x 1.8+32(?)
     
  11. thornev

    thornev Well-Known Member

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    Last edited: Jan 8, 2019

     

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  12. 1rebmem

    1rebmem AK Subscriber Subscriber

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    LOL...... metric is so much easier Larry!
    Just stop fighting it.
    Change is good!!

    Jef
     
  13. gadget73

    gadget73 junk junkie Subscriber

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    its the SI (System International) aka metric temperature unit. Units are something of an arbitrary thing. One guy picked the freezing point of seawater and what he thought was body temperature as two points on the scale. The other guy picked freezing and boiling of water. Why one won over the other as the scientific standard is probably a long and boring topic. Or it just could be that whoever picked it wasn't near the ocean.
     
  14. fred soop

    fred soop Super Member

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    Celsius units are not arbitrary. One calorie will increase the temperature of one gram of water by one degree C.
     
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  15. Pio1980

    Pio1980 AK Member Subscriber

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    Was that standard established before, after, or with Celsius?
     
  16. gadget73

    gadget73 junk junkie Subscriber

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    Still arbitrary. Why water instead of brine for example? It was decided somewhere along the way to define the units in a particular manner, but it could have been defined in any number of other ways. SI is designed to "interlock" the various units but it was a purposeful decision to make it that way.
     
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  17. fred soop

    fred soop Super Member

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    It probably started with 0˚ as freezing and 100˚ as boiling, then the calorie was defined afterward.
     
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  18. Linehand

    Linehand AK Subscriber Subscriber

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    Heres how I set my 800c if it adds to this thread.

    IMG_2316.jpg
    IMG_2318.jpg

    The fans are pulling, RPM increases with temp. At lower to lower-mid volumes, the fans run at idle. I like to think this might help me catch a problem should the fan/fans run up unexpectedly

    Also, you can see the bias test points on the heat shield behind the output transformers. Those are just butt connectors, shrink tubed, and a little hot glue to hold them in place. All easily reversible.

    I'm with Larry

    Metric numbers are easier to work with, but who needs that euro trash :rolleyes:
     
    Last edited: Jan 12, 2019
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  19. trainbuftony

    trainbuftony Electron Herder Subscriber

    I prefer the metric system, however i work at an american machine shop with inches, and only inches, and thats the way it is. No changing it folks, a mans gotta know his limitations. Nobody is going to sell their bridgeport milling machine in order to convert all their drawings to metric, so im here subdividing inches for the foreseeable future.
     
  20. thornev

    thornev Well-Known Member

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    I grew up on inches, feet, yards (and in some wonderful "back" yards) and miles. No matter how hard I try to become diverse, I still have to look up how many kilometers to the mile (and alas - it's the apolitical decimal system!). If I ever have to go live in Europe, I'm in big trouble. Haha. Thorne
     

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