Another Time Delay relay

Discussion in 'The Projects Forum' started by Rukahs, Feb 3, 2015.

  1. Rukahs

    Thread Starter New Member

    Dec 25, 2008
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    I'm trying to make a NOTC relay. I found this:
    http://forum.allaboutcircuits.com/threads/time-delay-relay.22874/
    but none of the links to the actual circuit are still good.

    I have a vague idea of what the circuit should be given the discussion about it I was just hoping someone had a working picture of the circuit.


    That said, what I really would like is to make the switch in the picture close after some time.
    standby5.jpg
    (picture from http://www.valvewizard.co.uk/standby.html) Just like the link of where the picture is from I'm trying to slow the application of HT to a tube amplifier. Really what I would like is to just flip the ON switch for the amp and have the heaters turn on instantly, then have that switch close after 15~30 seconds automatically. Because of this, a very ideal circuit would be something that is powered by 120VAC (turning the amp on).

    Any ideas on how to make such a thing would help.
    Thanks all
     
  2. #12

    Expert

    Nov 30, 2010
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    First problem: We're not allowed to make power circuits directly off the wall outlet.
    Second problem: You did not say what voltage the high voltage is.
    Third problem: Nobody knows if your transformer has enough power left over in the filament winding to build a delay timer, or what voltage is available in the filament winding.
     
  3. Rukahs

    Thread Starter New Member

    Dec 25, 2008
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    1) Why?
    2) I haven't measured it yet, it's probably around 300VAC, could be higher. I didn't take a look yet because that's just picking the right relay. I wanted to get some ideas on how to control the relay first.
    3) nor do I, wasn't planning on using it.

    I really just wanted the circuit diagram to get ideas on how to make an NOTC relay (that was my idea to solve the problem)
    The rest of the information is if someone has a better idea on how to make the above circuit automatic, I don't want to flip two switches, just the one.
     
    Last edited: Feb 4, 2015
  4. #12

    Expert

    Nov 30, 2010
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    1) website rules, also known as, "Terms of Service".
    2) 300 VAC rectifies to about 424 volts. Picking the right relay for that is not child's play. It might turn out to be something bulky that needs more than 100 ma to fire it. If you try to pull 100 ma off the 424 volt DC, you have to waste 42 watts of power, and tube transformers don't usually come with that kind of surplus power.
    3) If we can't use the wall outlet, and we can't use the filament winding, we have to use the 424 volts DC or install another transformer.

    There is a way to use a high voltage mosfet to ramp up the supply to the tubes, but it will use up a few (3 or 4) of the 424 volts to do that.
     
  5. Rukahs

    Thread Starter New Member

    Dec 25, 2008
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    1) ok, got it, I just read the ToS, and from now on, anything we talk about now is connected to a 1:1 transformer and thus 120VAC *AFTER* a transformer

    2) we can't use the HT anyway since the modification is specifically designed to limit HT, that R in the above diagram is going to be 100kOhm, when the amp gets turned on instead of having a ~400VDC supply, with the switch open it will be significantly lower.


    I'd like to know more about what you're thinking with the MOSFET.
     
  6. #12

    Expert

    Nov 30, 2010
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    ..........
     
  7. Rukahs

    Thread Starter New Member

    Dec 25, 2008
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    That's a pretty slick circuit.
    You fiddle with the ramp time by changing R right?
     
  8. #12

    Expert

    Nov 30, 2010
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    It's a picky little circuit.
    If you use much more resistance, the capacitor will leak the current away and never charge all the way. If you use much more capacitance, the capacitor will leak the current away and never charge all the way. You can decrease leakage by buying a higher voltage capacitor, but I don't remember seeing any 600 volt electrolytic capacitors.

    Here you go, $31:http://www.mouser.com/Passive-Compo...0wqt0Z1z0wqruZ1z0wrkgZ1z0wqroZ1z0wrk9Z1yyvtw3

    Maybe a 600 volt film capacitor. At that size, they cost about $100.http://www.mouser.com/Passive-Compo...0x4kvZ1z0x762Z1z0x6efZ1yyvtw3Z1yx4awjZ1yx4awu

    That means you have to mess with the resistance. 22 megohms costs the same as 1 megohm. Let's try a 1 uf film cap: $4.14 plus shipping

    http://www.mouser.com/Passive-Compo...Z1yx4awjZ1yx4awuZ1yznbzsZ1yzmkew&Ns=Pricing|0

    Just try it with a filter cap that you bought for the B+ and see how it works.
     
    Last edited: Feb 4, 2015
  9. Rukahs

    Thread Starter New Member

    Dec 25, 2008
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    I'm definitely going to play with that circuit. I think messing with the HT DC is easier in my situation, it's a store bought amp and the actual leads to the transformer are difficult to get to.
    Thanks for the MOSFET idea.

    In the interest of completeness for the forum, anyone searching, and my personal knowledge.
    How would one make a time delay circuit given AC power input (arbitrary voltage, post transformer)?

    I've found this but that's for DC input. (I'm also assuming this is similar to the dead links in the first post)
    (original link: http://electronics.stackexchange.co...a-12v-relay-for-few-seconds-after-power-is-on)
    oC2nj.png

    But how would one make something similar given an AC power source?
     
  10. Reloadron

    Active Member

    Jan 15, 2015
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    A Googlee of time delay relay tubes will bring up some interesting stuff, especially Amperite stuff. Years ago before all the new solid state timing most vacuum tube systems used a thermal type relay in a glass envelope to delay the B+ until the tube filaments were all hot. I remember around 20 to 60 second delays. The old ones used the 6.3 or 12.6 filament voltage but I think Amperite still makes a version that uses a 120 VAC (or DC) heater.

    Amperite Catalog

    Some Google Results

    Ron
     
  11. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Why do you think you even need a delay between the time the filaments are heated, and the B+ coming on?
     
  12. Reloadron

    Active Member

    Jan 15, 2015
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    Actually beats me as tens of thousands of vacuum tube TVs, Radio Receivers, Transmitters and just about any test, measurement, and diagnostic equipment had the tube filaments and B+ all come up at the same time. There seems to be a belief that it extends tube life using a delay and prevents "chunk emission" off cathodes. :)

    I do remember many of the 60s and 70s vintage Tektroix Oscilloscopes used a delay tube for the B+ but personally I never saw any merit to it. Today it seems popular with the audiophile and musician groups for their tube amplifiers. I believe their conviction is that the delay extends tube life and tubes, unlike many years ago, are expensive. Beyond that Mike, beats the hell out of me?

    Ron
     
  13. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Me too. This is like O2 free speaker wires... If the cathodes ain't hot enough to emit, why do you need to protect them from emitting...

    Back in the days of 5R4 or 5U4s, the B+ came on at the same time cathodes heated up :)
     
    Last edited: Feb 5, 2015
  14. #12

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    Nov 30, 2010
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    That drawing in post #9 has a time constant of 1.55 seconds and requires a separate DC power supply to work. (also, the relay is drawn backwards.)
     
  15. crutschow

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    Mar 14, 2008
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  16. #12

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    I'm open to the idea that you might arrange a circuit to delay by 30 seconds but I don't think you can buy thermistors rated for 0ver 400 volts. This is not going to be obvious how to arrange the circuit.
     
  17. Rukahs

    Thread Starter New Member

    Dec 25, 2008
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    Those are actually kinda cool.

    I got bored and wanted to fiddle with some electronics?
    I actually needed to add some cathode bypass caps. I figured while I'm taking it apart and soldering new stuff in, why not make more changes.

    You wouldn't, but it would limit inrush current to the caps, really I'm still just bored and looking at fun things to do with circuits.

    Yeah, that's what my math shows too. So how do I make that with a separate AC power supply?

    Yeah, I thought about those a while ago, digikey doesn't have a great selection of NTC stuff capable of dissipating more than 3 watts
     
  18. #12

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    Nov 30, 2010
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    Yeah, that's what my math shows too. So how do I make that with a separate AC power supply?

    It needs a DC supply. That's why I was asking about the filament winding (to steal some power for this circuit). No filament current available? Add another transformer as in post #2.
     
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