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Author Topic: kay 720 short hunt  (Read 20026 times)

g1

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Re: kay 720 short hunt
« Reply #15 on: July 01, 2015, 12:45:25 AM »
I guess I will just have to be disappointed and you will have to carry on in the mistaken belief it is a test device. ;)
I realize it is not intended to be a test device.  But when something acts as such on occasion, incidentally, why not use it to your advantage.
Consider the example I was referring to.  The bulb lit up with the rectifier tube in place, but did not when the rectifier tube was removed.  Had he used fuses, the conclusion would have been the same:  fuse blows with rect. tube in, does not blow with rect. tube removed.  By logic we conclude that the fault is after the power transformer.
The bulb limiter has served an unintended function, and has in fact been part of a test.
Yes, as Enzo pointed out, it has limitations.  But that is not to say it can't serve more than one function.  A fuse can serve as a "go/no-go" current measurement, in the case above, the bulb did the same.
  Your unequivocal statement was too sweeping and misleading in my view.  Had it not been absolute, I would not have been so opposed to it.
  We must make the most of the tools we have at hand, and sometimes that means using them in ways they may not have been intended for.
  I don't believe the bulb limiter is a test device, but my belief can not prevent it from occasionally being so.
« Last Edit: July 01, 2015, 12:48:39 AM by g1 »

DrGonz78

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Re: kay 720 short hunt
« Reply #16 on: July 01, 2015, 02:06:01 AM »
Of course the dim bulb tester has limitations. It limits current for one...  :lmao:
“A person who never made a mistake never tried anything new.” -Albert Einstein

J M Fahey

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Re: kay 720 short hunt
« Reply #17 on: July 01, 2015, 05:24:27 AM »
Agree that not a measurement instrument by itself, although lamp blinking and later stable brightness and colour give me a reasonable idea about how much the amp is trying to pull, at least I can distinguish between 4 broad areas:
* not even blinking : something open, maybe a fuse but sometimes a blown open rectifier or pulled connector, etc.
* blinking, then stabilizing red or dull orange: what we expect to see.
* blinking, then orange or yellow: not a full short but sensibly higher than normal consumption: maybe an overbiased but otherwise normal amp or there is some DC (say a couple Volts)  present at the output (load connected) or blown (shorted) transistors but also blown (open) emitter resistors so drivers are carrying the load, in that case I expect to see some smoke after a minute or two, or hear driver transistors exploding or at least cracking, hopefully the bulb limiter (which won't prevent that for long)  at least tells me to turn amp off befor other parts getb damaged .
* white lamp, full power: gross short.
Not bad for such a simple device.

But the main function is to let me measure *something*  , impossible with a fuse which blows in milliseconds.

At least I can check whether power rails are reasonably normal (say +/- 30V where I'd expect +/- 40) or dangerously low (say +/- 12 or 15V in the same situation) or indicating a shorted semiconductor  (say +/- 2V or thereabouts) or a GROSS short , +/- 0V (or a few mV).
Or whether there is DC at the output or not.

Admittedly not a "measuring instrumant" but they give me  a very broad indication and let the multimeter provide the actual numbers.

LateDev

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Re: kay 720 short hunt
« Reply #18 on: July 01, 2015, 06:29:39 AM »
I guess I will just have to be disappointed and you will have to carry on in the mistaken belief it is a test device. ;)
I realize it is not intended to be a test device.  But when something acts as such on occasion, incidentally, why not use it to your advantage.

Yes, as Enzo pointed out, it has limitations.  But that is not to say it can't serve more than one function. 

Both statements are of course correct, but from my reading on here, the limitations of the bulb method of testing are not pointed out.

The bulb is there to stop you blowing fuses and in some cases components, however it must never be thought of either as a protection device for everyday use or a test device for the many that don't understand its limitations or even why it is used.

 Yes it does have its uses in testing,providing you use it correctly, which many people don't. I even use the light bulb method for a load when testing, but I know its limitations so am aware of what to use it with.

I have seen others say that their amp distorts and the bulb lights up when they crank it up and play. They take this as some kind of fault.

For most people the light bulb must only be considered as a fuse saver, As Enzo stated earlier "My screwdriver is very handy but sucks at driving nails."

Enzo

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Re: kay 720 short hunt
« Reply #19 on: July 01, 2015, 07:50:18 AM »
You have to keep in mind that in the context of this forum, it has been explained many times over.

ilyaa

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Re: kay 720 short hunt
« Reply #20 on: July 01, 2015, 11:17:49 PM »
well, bulb-limiter aside -

i popped in a separate 47uF cap for the time being instead of the first section of the can and things are looking and sounding good -

looks like it was a shorted filter cap - didnt realize part of the big multi-section can could short....but i guess it can!

Enzo

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Re: kay 720 short hunt
« Reply #21 on: July 02, 2015, 01:28:22 AM »
Why would a section of the can cap not be able to short?  ANY cap can short.

LateDev

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Re: kay 720 short hunt
« Reply #22 on: July 02, 2015, 06:09:25 AM »
This is just a number of caps in the same can for convenience and cost.

Having a look at how a cap is constructed may help you to understand more about these things. Just do a search for Electrolytic Cap Construction. then imagine an insulator around each cap. In a filter can, they just connect all the cathodes together for convenience.

Some companies specialise in different filters for different applications and may present you with 2 tabs and a ground, yet inside there will be 2 caps and an inductor between the caps, any of which can individually blow.

I would imagine Enzo knows the construction of these cans, just as I do, which is why we have both said replace the whole filter circuit. With one cap inside already going short, the likely outcome would be that the other cap may go as well.

J M Fahey

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Re: kay 720 short hunt
« Reply #23 on: July 02, 2015, 09:56:07 AM »
Some companies specialise in different filters for different applications and may present you with 2 tabs and a ground, yet inside there will be 2 caps and an inductor between the caps, any of which can individually blow.
Sorry but you are confusing ilyaa .
You are mixing this kind of multi electrolytic cap, which ilyaa has in his 50 years old amp:

where capacitance is measured in microFarads, is electrolytic and so is polarized (DC rated only)... and has NO internal inductor of any kind, with this modern EMI/RF/Digital interference filter which does have picoFarad measured caps, joined by internal inductors.

The caps are anything but electrolytics, and are meant for direct AC mains use.

A very different thing.

A typical schematic of such filters is:


Quote
I would imagine Enzo knows the construction of these cans, just as I do
I bet Enzo does ;)

LateDev

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Re: kay 720 short hunt
« Reply #24 on: July 02, 2015, 05:26:48 PM »
 You are mistaken. Just because you have no experience with these, don't automatically think someone else is talking of something different.

As we are talking about power supply smoothing, why on earth would you assume that a mains filter is suddenly being talked about.

 A long time ago Pi filters could be had in a single can for filtering and smoothing power, I did think that Enzo may have come across these at some point in the past.


Enzo

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Re: kay 720 short hunt
« Reply #25 on: July 02, 2015, 08:51:45 PM »
Quote
Some companies specialize in different filters for different applications and may present you with 2 tabs and a ground, yet inside there will be 2 caps and an inductor between the caps, any of which can individually blow.

When you said that, that is why Juan said this:

Quote
You are mixing this kind of multi electrolytic cap, which ilyaa has in his 50 years old amp
:

I will happily believe you didn't mean the things Juan mentioned, but I can see why he would say that.  I was confused by it myself.

I have never seen a multisection can cap in a guitar amp that included a choke inside.  Especially from the era of the amp we are discussing.  There are or have been specialized parts, but guitar amps use real common stuff, especially basic amps from that era.  I have seen resistor/capacitor combination parts in real old amps, like the 1930s.  And in my work in RF I see various parts that would make no sense in audio.

Juan won't toot his own horn, but he is a design engineer and a commercial manufacturer of professional audio equipment, as well as a guy just interested in amps, so I would hesitate to assume he is ignorant of the parts we use.  it is one thing to not understand something you say, but another thing to think him inexperienced.

LateDev

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Re: kay 720 short hunt
« Reply #26 on: July 03, 2015, 07:26:34 AM »
 I didn't say he was inexperienced at all, I merely stated he had no experience of something.
Quote
You are mistaken. Just because you have no experience with these, don't automatically think someone else is talking of something different.

By stating as a fact I had said something wrong, is incorrect and should never have been put in the fashion it was.
Quote
You are mixing this kind of multi electrolytic cap,
A statement of fact.

He could just as easily have stated, that his experience was of the first type only, and he had no experience of the type I had stated, or in fact warned ilyaa not to confuse a mains filter with the type of cap he showed first, which would have been more helpful, Instead he decided to state I was wrong and he was right.

As far as someone not blowing their own horn, it matters little to me what his pedigree is, just how he conducts himself. I can obviously see he wants to be helpful, but it should never be his aim to put someone else down, because of his own misconceptions.
Suffice to say I have had experience in all the areas you have stated he has, plus quite a few more in both pro audio and commercial electronics.
« Last Edit: July 03, 2015, 08:03:01 AM by LateDev »

nosaj

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Re: kay 720 short hunt
« Reply #27 on: July 03, 2015, 08:50:31 AM »
Quote"Instead he decided to state I was wrong and he was right.

As far as someone not blowing their own horn, it matters little to me what his pedigree is, just how he conducts himself. I can obviously see he wants to be helpful, but it should never be his aim to put someone else down, because of his own misconceptions.
Suffice to say I have had experience in all the areas you have stated he has, plus quite a few more in both pro audio and commercial electronics."Quote

Sounds like someone's ego got bruised.  maybe you need to go back and re read to see what your goal really is. That your right and he's wrong?  It's kind of time to let this go.


nosaj

g1

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Re: kay 720 short hunt
« Reply #28 on: July 03, 2015, 12:16:55 PM »
  Please keep in mind that this is a guitar amp forum, and we speak in that context here.
  No one has ever seen a cap can with built in coil in any amp similar to the one in question.  So we don't talk about it as an option because of the context.
  To speak of esoterica it should to be mentioned as such.

LateDev

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Re: kay 720 short hunt
« Reply #29 on: July 03, 2015, 01:03:46 PM »
  Please keep in mind that this is a guitar amp forum, and we speak in that context here.
  No one has ever seen a cap can with built in coil in any amp similar to the one in question. 
That is a fair enough statement, which I can accept, and I was speaking in terms of guitar amps, but if as you say no one has seen one, then that is acceptable, to tell me I have not seen one or am mistaken is just a misconception.

Sorry I did not mean to bruise anyone's egos, but apparently have.

I found your statement that you have not seen such a device acceptable, just accept that I have seen one, and let it go at that.