John Curl's Blowtorch preamplifier part II

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Either this HAS happened, or it has never happened.

Absolutely, yes. And much more so before I learned a lot about science. Still, there are lots of things I don't understand. Buy I may not be like most people in that I am quite comfortable with accepting when I don't know something. I don't know if god exists for example, I have no way of knowing. That's okay with me. Other people might need to find some way of resolving that.
 
bear said:
Here's a somewhat interesting tale.

A ham radio friend says that to find the best support for a wire antenna, when choosing amongst trees; the way to do it is to put a portable radio next to the tree, like ON the tree surface (bark). The one(s) that boost the radio signal the most are going to result in the best wire antenna that is strung between said trees. keep in mind that the antenna is not connected electrically to the tree in any way. It's very well insulated.
Unlike audio folk, radio amateurs have to pass a technical test. Despite this, many of them seem unable to understand antennas (and transmission lines) so myths abound. Just like audio, there are people who make their living selling stuff (usually antennas) to radio hams (and even some radio professionals) accompanied by a good story despite boring engineers pointing out that the claims are 'creative'.
 
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Unlike audio folk, radio amateurs have to pass a technical test. Despite this, many of them seem unable to understand antennas (and transmission lines) so myths abound. Just like audio, there are people who make their living selling stuff (usually antennas) to radio hams (and even some radio professionals) accompanied by a good story despite boring engineers pointing out that the claims are 'creative'.
My father began his electronics career doing ham radio in his little Idaho town. He remained a technically rather weak engineer, but had strong opinions. It was best not to challenge him, as he did not take criticism well at all.

When he started to express himself on where the energy was in transmission lines, it was advisable to remain silent and let the subject play out of its own accord.

He had also assigned a cause to episodes of loud 60Hz hum from a JBL SA600, one of the early solid-state integrated amps that exploited the newly-available silicon PNP power devices, and with a topology that Bart Locanthi attempted to patent (unsuccessfully). He had accounted for the hum saying that it was due to electrolytics not "forming", and would cycle the power to get it to go away for a while. In its way it was a nearly-nonsensical explanation, but as he kept up with the phenomenology it got ever-deeper roots in his mind. If the hum had finally not gone away he might have taken the unit out of service and tried changing out the supposedly defective caps, to discover that they were still fine.

Eventually he upgraded to some other amplifier, and I inherited the SA600. I started to get the hum one day and finally determined the origin: intermittent shell connections of the RCAs. I probably never bothered to correct his spurious theory. Of course what was happening was the power cycling transients tended to punch through the oxide barriers of the RCAs and restore a reasonable connection for a while. Squeezing down the plugs after cleaning the jacks provided a long-term solution.
 
Unlike audio, amateur radio tends to deal with mostly lower order effects, not much in terms of higher order effects. There are likely some exceptions, maybe in GHz work, I don't know, since I'm not involved in that.

Wait, I do I have that backwards... 1st order is lower order, right?
Where's that textbook now that I need it??

Ham radio is mostly akin to making a big amp and a loud loudspeaker. The amp part being fairly easy to do. Nothing in the <0.001% IM or THD to think about. Very little in terms of "capacitor choice", usually a very narrow bandwidth where intelligence (the ability to be heard) is primary over all else.

Antennas are "voodoo". It's only fairly recently that rather crude simulation packages are available out in the "amateur world"... and there is little that I know of that will predict how well a given antenna (properly designed) will actually "play" from a given location. Notwithstanding the "dummy loads" hawked for mobile use and as wire antennas, even the classic aluminum entry level verticals that were sold in the 60s and 70s as "space saving".

These days any ham who is into the hobby in a way that is equal to what we do here on DIYAudio has very good antennas, properly designed and reads and applies the same sort of information of the type and nature of what we are discussing.

Back a few months ago, in the winter, I was able to have a QSO with several European stations on 75m, ~3.700mHz. They were running "4 square" vertical antennas (phased verticals) and one had a rotatable Yagi with a boom of astounding length! With a web page to show it off too...

And there are SDR radios, and Class E 90+% efficient AM transmitters too... that's just HF. The guys on UHF are in a different zone entirely.

So, sure there are newbies that buy commercial wire antennas because of the ease, and they don't have much to do... very few hams these days are buying snake oil antennas - at least in the USA. Can't recall when I've seen one advertised.

Gotham beams and verticals are now a historical point of amusement.

:)
 
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Unlike audio folk, radio amateurs have to pass a technical test. Despite this, many of them seem unable to understand antennas (and transmission lines) so myths abound. Just like audio, there are people who make their living selling stuff (usually antennas) to radio hams (and even some radio professionals) accompanied by a good story despite boring engineers pointing out that the claims are 'creative'.

Yes, but the hurdles are not too high. I made my ham radio license a few days after my 18th birthday,
I was not allowed to do it earlier.

And yes, we had a producer/seller here in .de of an Australian designed multiband yagi
who claimed all sorts of wonderous things that simply were not true. It was not a bad
antenna as far as physics allow, and our group used it as it could easily handle our
"slightly" more than legal power. That capability was probably the real reason behind
the strong signals from that antenna type. :)

There was an excellent review of this antenna in our club newspaper from a guy who was
considered the Pope of field strength measurements even at competitors like R&S,
but it showed that the emperor was only pretty, but still nekkid and the manufacturer
sued the **** out of the reviewer, leading to an end of his article series that I personally learned a LOT from.

To come to an end: trees are just absorbers; stay away from them with your antennas;
gain comes from height and directivity, and even a dipole has some.

regards,
Gerhard, DK4XP
 
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You said skin effect and there it doesn't, I don't normally waste my time back searching for comments so lets others. The signal is NOT forced into the oxide at audio frequencies re. the skin effect.

That is correct. you win the prize. Now thats over with... I am still talking about oxidation. Skin affect comes into play when the oxide layer (a semi-conductor - if from copper) contains the HF part of the signal... above about 8KHz. Now in a perfect world, you have only copper and no oxide. then it doesnt matter.

But we have all seen a new bright shiny copper penny and soon afterwards, it is dull from oxidation. Those wires you havent changed in 17 years nor cracked any connections in awhile, can be a source of distortion. In addition, I said that connectors were a bigger source of problem due to oxidation and corrotion... there all the frequencies have to break thru the oxide layer to pass from male to female part of the RCA connector. Recall, earlier, I told how I could hear and find an offending contacts of a speaker fuse/holder by hearing the distortion the one speaker signal had to pass thru.



THx-RNMarsh
 
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Antennas are "voodoo". It's only fairly recently that rather crude simulation packages are available out in the "amateur world"... and there is little that I know of that will predict how well a given antenna (properly designed) will actually "play" from a given location. Notwithstanding the "dummy loads" hawked for mobile use and as wire antennas, even the classic aluminum entry level verticals that were sold in the 60s and 70s as "space saving".

These days any ham who is into the hobby in a way that is equal to what we do here on DIYAudio has very good antennas, properly designed and reads and applies the same sort of information of the type and nature of what we are discussing.

:)

Antennas are not voodoo, few things can be computed as exact like antennas.
The NEC program is what everybody had; I compiled it on a 10 MHz 80286/87
running Interactive Unix with a 70 MB hard disk and 2 or 8 MB of RAM, cannot
remember.
Every serious CAD package has a full 3D solver nowadays, be it CST, ADS,
AWR or whatever. And hams do have access to them since they are in the
industry.

regards, Gerhard
 
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That is correct. you win the prize. Now thats over with... I am still talking about oxidation. Skin affect comes into play when the oxide layer (a semi-conductor - if from copper) contains the HF part of the signal... above about 8KHz. Now in a perfect world, you have only copper and no oxide. then it doesnt matter.
This should be exceedingly easy to test. take 2 lengths of coax off a reel and terminate. Strip the outer insulation off one and oxidise it. (heat , salt, vinegar etc). Measure the 2 cables. Kirchoff says an oxidised sheath will be same as oxidised centre.

But we have all seen a new bright shiny copper penny and soon afterwards, it is dull from oxidation. Those wires you havent changed in 17 years nor cracked any connections in awhile, can be a source of distortion. In addition, I said that connectors were a bigger source of problem due to oxidation and corrotion... there all the frequencies have to break thru the oxide layer to pass from male to female part of the RCA connector. Recall, earlier, I told how I could hear and find an offending contacts of a speaker fuse/holder by hearing the distortion the one speaker signal had to pass thru.

THx-RNMarsh

I don't buy this. If it is oxidised enough for a diode effect then you will get almost no signal, just the peaks on a line level interconnect. You don't have high enough voltage to punch through except on speakers and even then when cranked. Or am I missing something?
 
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Vf on oxidized contacts not necessarily .65 V

Shitty contacts are a real issue.

I won't discuss the physics - I am not qualified to do so.

However, I lived in Durban, South Africa for many years. It has one of the most corrosive atmospheres anywhere - especially in the areas right next to the sea. 12 months of that and RCA connectors were usually white with corrosion and you definitely had to tweak the connectors to keep things sounding nice.
 
I won't discuss the physics - I am not qualified to do so.

An honest man, a note to others don't put words together and make up stories for what's going on. Everyone has dealt with corroded/partially corroded contacts, as for signals "breaking through oxides" is just making stuff up again without an understanding of what is complex physics.

BTW a cuprous oxide diode has about a .2V drop any actual metal to metal path in parallel at modest currents will prevent any diode action. It is reasonable to believe at audio line levels the contact would have to become oxidized to a pathological level to show any effect.

I will also remind you of the EM pico-voltmeter (notice last setting is 1nv full scale) which has solid untreated pure copper input lugs.
 

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Vf on oxidized contacts not necessarily .65 V

.

Never said it was, was looking at the graph Richard posted for oxidised copper that showed a Vf around 0.3V and 50V or more needed to break the oxide. With a 10dB crest factor you'll get precious little music over that 0.3V.

Shitty contacts I will agree are real, but its a gross level effect IMO not something subtle as seems to be claimed.

Still reckon 5 pin din is a better connector than RCA. Maybe Julian V was right...
 
Antennas _are_ voodoo when near the Earth and otherwise non-ideal. Good models for perfect antennas (sic) exist, just as good acoustic models for perfect rooms exist.

The real world is messy and we need to finely judge when to abandon our linear idealized models.

"Camelot!"
"Camelot!"
"It's only a model."

All good fortune,
Chris
 
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I may spring for a recent book on near-field EM, even though I have no intention of designing antennas, and as well it is an Artech publication, whose books I have found fairly disappointing most of the time.

But that area is where a lot of people experience difficulty, including Nikola Tesla.
 
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This from the wiki for "metal rectifier" is interesting: "The principle of operation of a metal rectifier is related to modern semiconductor rectifiers (Schottky diodes and p–n diodes), but somewhat more complex. Both selenium and copper oxide are semiconductors, in practice doped by impurities during manufacture. When they are deposited on metals, it would be expected that the result is a simple metal–semiconductor junction and that the rectification would be a result of a Schottky barrier. However, this is not always the case: the scientist S. Poganski discovered in the 1940s that the best selenium rectifiers were in fact semiconductor-semiconductor junctions between selenium and a thin cadmium selenide layer, generated out of the cadmium-tin metal coating during processing.[1][2] In any case the result is that there is a depletion region in the semiconductor, with a built-in electric field, and this provides the rectifying action."
 
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