It pays to read the manual!!

Discussion in 'General Electronics Chat' started by MaxHeadRoom, Apr 23, 2015.

  1. MaxHeadRoom

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    A while ago my son, who plays in a band, acquired a quality second hand British made tube amp.
    He seemed to be going through power tubes, a matched set of four replaced at a time.
    The amp has two ON switches, Power on 1 or 0, and a stand by SW. 1 or 0.
    Now intuitively, to me, you would put the Stand by switch on, wait a couple of minutes and then the main power on.
    After getting me to look at it after the last failure, I downloaded the manual.
    Evidently he (and I) had it backwards.
    The main power is switched ON followed by the standby ON after 2 minutes.!
    Power down in reverse.
    Hopefully this cures his expensive replacements.:(
    Max.
     
    Last edited: Apr 23, 2015
  2. #12

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    It will. Hitting a cold power tube with B+ poisons the cathode.
     
  3. cmartinez

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    Wouldn't it be better if you just designed and built a sequence-timer circuit and use a single switch instead of performing that operation manually every time your son intended to use it?
     
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  4. AnalogKid

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    I'm sure it needs a 555.

    ak
     
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  5. #12

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    If only you had told that to the VOX corporation, about 60 years ago. :D
     
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  6. cmartinez

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    Gosh... my first original idea... 60 years too late! ... :confused:
     
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  7. wayneh

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    My old Fender Tremolo amp is the same. Power-on first to warm up the tubes, then you come off stand-by a minute later. I always wondered whether you really need to hit stand-by before powering off, but it's good practice since it puts the toggle switch back to the start-up position. I don't believe you need any time lag between standby and power-off.
     
  8. MikeML

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    Convince me. What is the physics behind this statement?
     
  9. #12

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    What? Convince a person that believes current flows from positive to negative how a vacuum tube works? :confused:

    It's all just a joke created by the British manufacturer and perpetrated on people so ignorant that they actually need to read the manual. :D
     
  10. MaxHeadRoom

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    I do know that a low filament voltage in some types of cathode material can ruin a tube in seconds!
    Max.
     
  11. MrChips

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    I'm surprised you would see it the way you did.

    To me, power is power.
    Hence controlling the standby switch with the power off would have no effect.
    Apply power first. I can see that the standby position ON or OFF is ambiguous.
     
  12. cmartinez

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    Ok... now I declare myself officially confused
     
  13. #12

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    "0" is off, "1" is on. The idea is to power up everything except the B+ first, then switch on the B+ after the filaments are warmed up. ("Real" engineers don't believe this has any merit.) The only tube that gets high voltage on its plate(s) when its cathode is cold is the rectifier tube..if it has one. Silicon diodes changed this to almost zero delay for B+, eliminated the rectifier tube, reduced the number of turns in the B+ windings on the power transformer, and eliminated the 5 volt winding for the rectifier filament.
     
  14. MaxHeadRoom

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    An understatement.
    Standby ON to me would mean In Standby Mode, Not actually powered and ready to operate?
    Max.
     
  15. MrChips

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    I know what you're saying. Many times people are not semantically correct.
    The way it usually works on every piece of equipment, STANDBY in the ON position means it is no longer on standby.:rolleyes:

    That is, the ON label is overrides what we accept as STANDBY.
     
  16. MaxHeadRoom

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    I do not use this equipment but apparently according to my son, all his acquaintances he has spoken to are/were under the same impression and evidently have been misusing their amps in the same way!
    Much of this equipment has been purchased second hand and is a few decades old, so manuals did not come with the units.
    Max.
     
  17. MrChips

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    I have not seen the instructions in the manuals but my intuition tells me that for full operation,
    both POWER and STANDBY switches must be ON.

    So the sequence for power ON is

    POWER STANDBY
    OFF OFF
    ON OFF
    ON ON

    and back track for power OFF, as you have already described.

    Coincidentally, last week I was at the local music store checking out some guitars and amps and that is exactly how I operated the amps.
     
  18. MaxHeadRoom

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    Evidently the unfortunate fact is that the majority of users of the equipment misinterpret the way to use it because of how the switches are portrayed and labeled, this would indicate that their needs to be a clearer indication of their usage.
    If I were a designer of such equipment, I don't see myself labeling it that way.
    Max.
     
  19. MrChips

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  20. wayneh

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    I don't see how there's any room for confusion. Warm up the tubes with the audio off, then turn on the audio. Seems intuitive to me, as MrChips noted in #17.
     
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