Heathkit W5m delay timer

[JimmyEJames]

Sorry for OP this thread stolen going to no where unless somebody here work for tube company and going to fix crap tubes!
I apologize to you taking bait!
Please all expert here loving argument please fix today no good tubes pop like fire cracker first turn on make noise no set of bias only last a week all just junk
Please take all this brain effort and fix tubes but not to argue!
Thank you
JJ

 

[JimmyEJames]

The photo just proved my point of thermal runaway.

My explanation of the physics and phenomenon was accurate and the application to your specific problem is left as an exercise for the reader.

You should start own thread not take OP thread away
JJ

 

[whoaru99]

.. thermal runaway.

There's never been any debate about that. But I'm OK that we disagree on the technicalities of why it is.

 

[Retrovert]

MOSFETs would in fact be ideal devices for ramping bias and screen grid voltages -- but you'd only need to ramp one of them to accomplish a soft landing at shut down (or soft start at turn-on). At shut down, you could ramp the Eg1 voltage up (more negative) to bias the tube into cut-off, but a more practical way would be to ramp the screen voltage down for pentodes, or the B+ down for triode and UL designs..

I see the value in that, but am unsure if this is optimal.

The islands of charge coalese during heating and then fragment on cooling. So we still have the possibility of current flow to the plate from an incomplete emissions surface if the tube is not put into cutoff. The issue is that as the space cloud is building or collapsing and the islands are coalescing or fragmenting that current could pull electrons from that surface. Pushing the grid into cutoff shuts down that flow. Yes, the screen will also do it, if we have a pentode, but I think it is better to do it at the grid because that forces the space charge to remain close to the cathode. And my feeling is that this will protect the cathode than if electrons are emitting from the surface to a farther away space cloud during the fragmentation phase. We don't want a lot of emission because that is from the irregular points on the cathode.

In any even, doing this for every tube requires a MOSFET per tube, and since it is only a voltage not a current a small one would do, and it is easy to add an extra one for the screen on any pentodes, belt and suspenders, what's not to like except some minor cost and wiring.

By placing the ramping MOSFET in the power supply section, the capacitance of the MOSFET would not come into question with regards to the audio circuits.

Yes, that could work for the screen in pure pentode mode, which had its own screen supply, but it would not address the screen in Ultralinear or tridode mode for pentodes, or any of the triodes, as in a splitter.

 

[Retrovert]

Light bulb filaments are tight coils like a long spring. There is no problem with tungsten being shaped for those. That slight wide angled loop in the tube heater end is nothing in comparison.

No, that is wrong.

Light bulbs fail because of hot spots induced from irregularities in the tungsten wire. Go read about it. You'll see.

 

[Retrovert]

You should start own thread not take OP thread away

Still on topic. The OP's question was, "Am switching from tube to solid-state rectification, and am installing a delay timer to avoid making bottle rockets". We're talking about delay, delay, and more delay. Just the reason behind that delay.

 

[JimmyEJames]

Still on topic. The OP's question was, "Am switching from tube to solid-state rectification, and am installing a delay timer to avoid making bottle rockets". We're talking about delay, delay, and more delay. Just the reason behind that delay.

No you talk pontificate run OP away not post in his own thread after page one one time on page two in post 40 when he giving up because you hijack with talk talk talk and never answer his simple question

OP ask specific question about specific board he buy and you come in with history lesson and theory and that hijacking and keep talking after OP say he not interested!

And you nasty if someone not want to agree with you all your way about subject you can do NOTHING about!
Hijack other person thread recite general knowledge everyone already knows
You sound ignorant person not say anything new just speculate hear own voice
NOT call you ignorant just you sound that way and egotist too
Just quoting other people's work
What is technical background?
What do you do for living?
But you owe OP apology and need to start own thread you take over his like it your lecure hall
JJ

 

[Retrovert]

No you talk pontificate run OP away not post in his own thread after page one one time on page two in post 40 when he giving up because you hijack with talk talk talk and never answer his simple question

OP ask specific question about specific board he buy and you come in with history lesson and theory and that hijacking and keep talking after OP say he not interested!

And you nasty if someone not want to agree with you all your way about subject you can do NOTHING about!
Hijack other person thread recite general knowledge everyone already knows
You sound ignorant person not say anything new just speculate hear own voice
NOT call you ignorant just you sound that way and egotist too
Just quoting other people's work
What is technical background?
What do you do for living?
But you owe OP apology and need to start own thread you take over his like it your lecure hall
JJ

That is an ad hominem attack.

en.wikipedia.org/wiki/Ad_hominem
Ad hominem (Latin for "to the man" or "to the person"[1]), short for argumentum ad hominem, is a logical fallacy in which an argument is rebutted by attacking the character, motive, or other attribute of the person making the argument, or persons associated with the argument, rather than attacking the substance of the argument itself.​

 

[whoaru99]

Yes, that is ad hominem.

But so is this...

Retrovert said: ↑
When you start posting well-reasoned facts maybe I'll believe you're in a position to comment on my work. All I see is a volume of one-liner postings to increase your posting count.

And, it is appeal to authority at the same time - a double whammy.

Double standards, I guess.

 

[Retrovert]

Yes, that is ad hominem.
But so is this...
And, it is appeal to authority at the same time - a double whammy.
Double standards, I guess.

Not at all. That is again incorrect. I am saying that your explanation is wrong and that you have not put forth a credible basis for it. You set forth a lot of opinion which conflicts with the science. I did not make any argument about your character, background, employment, etc. or demand details so that we could use those to weigh your arguments. That was the ad hominem to which I referred. I don't care about your background as it is irrelevant.

I, instead, said your explanations were incorrect and proposed alternate hypothesis with actual physics and materials science. You continually post your opinions without any science or hypothesis, and you have not addressed the science and physics I set forth. That suggests to me you don't understand the physics or the materials. You certainly never respond in any detail.

Again, my explanation of the flash as resulting for a higher-resistance bend fits the facts, fits the properties of tungsten, and fits the physics. You come back with opinion about coatings while failing to address the thermal conductivity physics I included.

I also believe you continually post to increase your posting count to unbelievable levels, and that you don't really want to discuss science or engineering, you just want to post a lot. Others have told me this as well. That isn't relevant except to explain why I believe you have not addressed the science I posted.

You misunderstand the appeal to authority fallacy. I have not appealed to any person as an authority in some other area and attempted to transfer that authority here. I have, instead, set forth physics which are readily verifiable. Physics is that which continues to exist even when you do not believe in it. Appealing to physics is not some sort of logical fallacy. Are you saying that my references to the Larson-Miller work is an appeal to authority? Those two wrote the book on failures from recrystallization and elongation in metals! Their work is the gold standard and is widely referenced. Go read it. I'm not saying that because they are experts in metals they know something about politics. I'm saying that their work explains tungsten's behavior and is controlling here.

Again, read my explanation of how tungsten can be damaged and how this creates hot spots, and refute it. My theory accounts for why the heater flash is only seen in tubes from certain factories and does not depend on the coating. It is simple and elegant. Your theory doesn't fit the facts, doesn't explain why we don't see the problem in all tubes, and doesn't address the specific mechanical structure of that tube with a bend.

Your theory must therefore be discarded in favor of the better theory. That is how science works. Your theory is incorrect.

QED.

 

[JimmyEJames]

Yes, that is ad hominem.

But so is this...



And, it is appeal to authority at the same time - a double whammy.

Double standards, I guess.

Hello whoaru99
Thank you for open mind
Only can be correct if you agree with Retrovert I do not understand point either
All this posting nothing to do with OP original question just vague connection to specific after market board fix now a platform for Retrovert's thought on matter
I not attacking any one just try to say start new thread about theory on tube flash possible fix and cause for issue
That is all I mean this is not discussion it is lecture even definition for ad hominem rely on someone else work quote dictionary like wise guy
I not attack Retrovert thoughts on subject just way he go about it
Other posters say what they think meet with no no no I am correct and you are incorrect
That is not discussion and even if so what is point?
Retrovert I am sorry if you feel that way but I am not only one that think argue just for sake of argue
Make design and put together kit for fix maybe others will buy
I am sorry you feel like attack on you not so just making my point about rudeness to other posters
JJ

 

[trobbins]

There's never been any debate about that. But I'm OK that we disagree on the technicalities of why it is.

Thermal runaway is not an appropriate term to use unless you put it in the context that other system and thermal influences are simultaneously counteracting the rise in temp, with the result that the filament does not thermally runaway and melt.

 

[trobbins]

Here is the closest still frame I could get from the initiation. As you see, the heating is well away (relatively speaking) from the weld and nearly equidistant, but not quite, from the coating. Why? Because the thermal mass of the bare exposed filament is much less than the weld area and materially less than the coated area. The picture of the heating is quite consistent with greater thermal mass towards either end of the exposed filament.

Whoaru99, it's worth stepping through the process from time = 0, so as to keep in mind all the dynamics at play. At t=0, all the filament is the same temp, as is the coating and terminal. Pretty much the highest power presented to any section of filament starts to heat the filament evenly at the start (given I squared, and I is an initial peak that reduces quite fast at the start, even though R will also start changing rapidly with time). That t=0 power can't dissipate away, as the section of filament next door is the same temp so there is no conduction along the filament, and there is no temperature differential for radiation transfer to occur). So until the wire temp rises substantially, radiation transfer is a little slow off the mark. Conductive transfer would be a faster mechanism, becoming significant as soon as a temperature gradient builds up along the wire.

So initially we have to wait for the thermal mass of the wire to increase in temp from the applied power. Given the effectiveness of conduction as a thermal transfer path, the filament near the terminal builds up a large temp gradient, as you point to in your image. Similarly, the filament that is coated is able to conduct in to the coating - the coating is not metallic, but the contact surface area for conduction is large, and RCA indicate that alumina is not too bad a thermal conductor - and radiation from the coating would be slow off the mark as well but a relatively large surface area makes it significant - so the rate of rise of temp in the filament that is coated is slower than for the uncoated filament. As such, a temp gradient along the filament also builds up in the region where the coating finishes, as you point to in your image.

The dynamic rise in filament temp, and the temp gradients along the filament, mean that pretty soon the hottest region of filament noticeably has more power dissipating in it than cooler regions, due to the strong temp coefficient of resistance of the filament and the common current level in all regions. So the strongest incandescence (temperature) is very much centred on the uncoated filament that is suitably distant from the cooler regions of the filament.

 

[muzzleblast]

To the point of the OP's original inquiry... Was there ever a MOSFET delay design & schematic offered (perhaps in another thread I've yet to discover)?
Or perhaps an ideal 2-stage delay/design that has since been completed?
Like many here, I have a set of Heathkit W4AM and W5M mono blocks and concerned with extending the original PT and OPT iron.

I tried to follow along with the various message threads but frankly, got lost in all the "design optimization". While an engineer, its been 40 years since I graduated from Texas A&M; I felt much of this topic morphed away from the point the OP had asked about and conversation had evolved into a need to "shoot the engineers and get on with production"... as we often say in my firm.

I do respect some of the members who were on this thread, and know they are well versed- more so than I- in tube circuit design & implementation.