In my day job I have designed handheld computer mainboards with integrated data radios, with RF antennas, switches and matching, automated satellite pointing controllers with 2GHz IF amplification, filtering and detection. I have spent many whole days in EMC chambers and fixed EMC non-compliances on the fly, without leaving the lab. My designs have sold in 7-figure numbers, despite being professional quality and price. So if I don't understand RF pretty well, I must be spectacularly good at cut-and-try.
Radiated emissions don't destroy DACs - they degrade the performance.
Putting an Ampere-level HF signal into a DHT filament (one side of which is grounded, out of necessity) and then an AF signal into the grid is going to radiate carrier and AF sidebands, regardless of any matching.
What spectrum have you measured around this device?
No harm at all!
But that isn't what I said.
I said (and say) that the idea of a high power HF heater is crazy, that is all.
The proposition is large, complex, and throws HF around everywhere in order to address a problem that nobody has actually seen.
If anyone is actually worried, or paranoid, that DC heat could shorten the life of a filament, I have an easier comfort solution.
Wire the filament poles of your valve socket in opposite polarity, for the L and R channels. Then at every year, or half-year that passes, swap the Left and Right DHTs over.
Works for real or imaginary effects.
Wire the filament poles of your valve socket in opposite polarity, for the L and R channels. Then at every year, or half-year that passes, swap the Left and Right DHTs over.
Works for real or imaginary effects.
Well, let's see. I am retired but, in my day Job, I was an RF Applications Engineer for Motorola..
Some of my accomplishments were on the earlier Cell phone. In particular the main portion of the receiver that allowed for
very precise tracking of the phones for the implementation of Spread Spectrum communications. That same concept is still
in use today even with GSM. I also was in on the original design of the GPS systems that Motorola. I really must think you are correct at cut and try because
you still think with a closed mind. Nothing can possibly work if you don't think it can. if you want to talk about screen rooms. I spent a good portion of my career in them as well. Shoot just on the hobby side of things I have work up to 12 GHz and have the equipment to do so. You talk about your designs selling in 7 figures. Do you have any understanding of what I just told you. my designs and concepts were implemented into just about everything RF that Motorola marketed for over 10 year. I once had the honor and pleasure to talk Bob Galvin, the CEO of Motorola into funding the fledgling GaAs program after he had decided to shut it off. Ron, I have taken my turn at standing on the high mountain. After all of the accomplishments you have just listed. Tell me where is it written that you have the right to shut off what you think shouldn't be discussed or what merit it holds. As far as measurements around the device. Not my chair. Talk to John Atwood. as far as the ******* contest we have been having, That's done. I will not waste any more time with you.
Jamie
Some of my accomplishments were on the earlier Cell phone. In particular the main portion of the receiver that allowed for
very precise tracking of the phones for the implementation of Spread Spectrum communications. That same concept is still
in use today even with GSM. I also was in on the original design of the GPS systems that Motorola. I really must think you are correct at cut and try because
you still think with a closed mind. Nothing can possibly work if you don't think it can. if you want to talk about screen rooms. I spent a good portion of my career in them as well. Shoot just on the hobby side of things I have work up to 12 GHz and have the equipment to do so. You talk about your designs selling in 7 figures. Do you have any understanding of what I just told you. my designs and concepts were implemented into just about everything RF that Motorola marketed for over 10 year. I once had the honor and pleasure to talk Bob Galvin, the CEO of Motorola into funding the fledgling GaAs program after he had decided to shut it off. Ron, I have taken my turn at standing on the high mountain. After all of the accomplishments you have just listed. Tell me where is it written that you have the right to shut off what you think shouldn't be discussed or what merit it holds. As far as measurements around the device. Not my chair. Talk to John Atwood. as far as the ******* contest we have been having, That's done. I will not waste any more time with you.
Jamie
You see and the only difference between your solution and others I have heard is instead of rotating the tubes add a switch to change the polarity.
You're twisting my words again.
I said HF heating was crazy, not that we can't discuss it. You are seeing what you want to see.
Goodbye.
Better yet, If people are paranoid that DC could shorten the life of a tube, then they shouldn't be using such expensive tubes.
That's like worrying about engine oil chemistry so that you can cut back on oil changes on a lamborghini. If the oil changes are killing you, then you need to find a different car.
But if the official datasheet of the actual tube says that the filament or the heater can be supplied with AC or DC WITHOUT any other note on drawbacks or change in specifications, it means that there is no difference in electrical performance. Why would one take and publish the curves of the 45 (and many other tubes) with DC heated filament if it were less than ideal? The final product has little to do with fabrication process and the getter inside the tube is there for a reason. Unless a tube has been sitting in a box for ages, lack of getter is not the reason why tubes normally die. Actually for the battery tubes, both power and signal tubes, it is specified to use DC only. I don't know the reason but the recommendation is clear and stiff!
I don't need articles or work from others to know that DC heating works because I have used it for at least 30 years without a problem whatsoever. Actually I have realized that I have seen longer life out of my tubes respect to what others tell. Easy to explain: lack of regulation brings shorter life. That is documented from the early ages....
I am not telling others that AC at line frequency is bad but surely one gets IMD which automatically means poorer performance regardless of personal taste.
Now, assuming that HF AC heating does not introduce some kind of weird distortion, is there any real advantage for using a complicated AC heating system? I can't see a reason but I not telling one should not do it. Everyone can do what he likes but justifying personal choices by dismissing other's solution with no proof is not really acceptable.
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I heat my preamp tubes with DC. The tubes are all indirectly heated types, such as 6922/6DJ8 or similar. I have a mechanical polarity reversal switch built inside the preamp's enclosure on the heater circuit, and every so often I'll remove the perf-metal lid on the preamp and flip it (power must be OFF when doing this). The DC source is a slow start circuit, and the tubes' heater voltage is ramped up slowly to avoid inrush currents. I've had the preamp for years and have not had any problems with tube failures so far. Heater-to-cathode voltages are well below the specified maximum for that. The preamp is a home-brewed 2-box one, and the only AC in the preamp box is the music. There is no hum whatsoever, and if there were any, I'd have to look outside the preamp for the source of the hum. That preamp knows the words, so it doesn't have to hum along with the music.
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Am I "anti" paranoid?
I extensively use TT (thoriated tungsten) tubes, even if its near to eighty-hundred years.
Nowadays mostly of these are expensive as if it were made of gold.
Each warm up-cool down degrading of filament (Miller-Larson effect) -regardless of heating process-, sooner or later it will be breaking.
So each turning on carries the risk to go to devil 150-200 bucks.
Who cares?
The life is too short to drink bad wine.
It's a hobby ... all of us want the best .. without enough good parts the the end result will be mediocre.
Carpe diem!
Same here. I started at Motorola in 1973 on the HT-220 line. I retired in 2014 as a Principal Staff Research Engineer designing high power LTE transmitters at 700 MHz. In between I spent a few years designing Nextel phones and police walkie talkies. Regardless, there are valid arguments on both sides of this "contest." At frequencies around 100 KHz the filament load is nearly purely resistive. The matching of the source (unknown amp) to the load (mostly resistive) can be easily accomplished with a broadband transformer wound on a suitable core. This allows for independent center tapped secondaries for each tube to facilitate current measurements.
Whether or not it is worth the effort or not is up to the individual builder. My testing was done about 20 years ago, and my personal decision at that time was that DC heating was the best choice for the given amp design.
Or a center-off switch ON-OFF-ON then every time you turn on the amp... just flip it in the opposite direction you did yesterday! Each ON position would flip the heater polarity opposite.
I can see where DC on a directly heated tube like the 300B could cause problems, since emission would not be of the same intensity over the entire length of the filament due to the changing DC potential across its length. With AC all of the filament gets exposed to the same thing, on and off, over time.Am I "anti" paranoid?
I extensively use TT (thoriated tungsten) tubes, even if its near to eighty-hundred years.
Nowadays mostly of these are expensive as if it were made of gold.
Each warm up-cool down degrading of filament (Miller-Larson effect) -regardless of heating process-, sooner or later it will be breaking.
So each turning on carries the risk to go to devil 150-200 bucks.
Who cares?
The life is too short to drink bad wine.
It's a hobby ... all of us want the best .. without enough good parts the the end result will be mediocre.
Carpe diem!
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Joined 2009
Paid Member
The filament rate of emission depends on the temperature of the filament material, and this temperature is a function of the current and resistance which don’t change along the length of filament with constant cross-section. There isn’t going to be any variation of emission along the filament due to the voltage gradient. In practice, there will be variations in the filament temperature due to different rates of heat loss from the filament along it's length, e.g.- the ends will be in contact with colder supports. For the purposes of this thread though, the emission can be said to be uniform and constant along the filament. Think of the case of a series string of identical power resistors, this will all have the same power dissipation, and in the same environment the will all reach the same temperature despite having a voltage gradient along the string.
Where the voltage gradient has an impact on the tube is to create a gradient in the filament-grid bias because the grid is at an equipotential (it should have a negligible voltage gradient of it's own) . This bias directly controls the cathode-plate current and the dc voltage gradient along the filament will result in a variation in the current flow between the filament and the plate depending on the geometry of filament-plate. This would happen with AC heating too of course.
Where the voltage gradient has an impact on the tube is to create a gradient in the filament-grid bias because the grid is at an equipotential (it should have a negligible voltage gradient of it's own) . This bias directly controls the cathode-plate current and the dc voltage gradient along the filament will result in a variation in the current flow between the filament and the plate depending on the geometry of filament-plate. This would happen with AC heating too of course.
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On this one it looks like I'm SOL. During the Autumn of 2019, just before COVID I decided to unload some of my stash.Just after the Earth cooled some people did use Ultrasonic Oscillators to heat tube filaments & heaters.
I've still got one of the specially constructed coils used. The circuit used a 6L6. I'll post a photo later.
I'd just turned 87, I'd been wondering what to do with my stuff. My heirs & successors have no idea what this is.
So a few boxes went out the door to a friend who runs a small business restoring old radios & auto radios from
peoples project cars. The device in question may have been in that lot.
I did find what looks like an early HV TV Flyback transformer.
But I do recall several articles published during the 50s describing circuits to heat some of the tubes of the day.
A single 807 running as a Class C oscillator is rated for 40 watts of output. That would easily heat a pair of 2A3s.
