modern vacuum tube uses? (other then high power/rf/audiophile) - Page 1
Forum section: electronics / general

author: SArepairman
author_rank: Frequent Contributor
timestamp: April 17, 2014, 11:02:18 pm
content: Are there any uses of vacuum tubes in electronics today other then for High frequency/high power ?I know they are often used in frequency and power applications, but do they have any niche uses in practical electronics, (other then adding intentional distortion to music)so, low power uses.do they have any interesting properties that transistors can't beat?

author: PedroDaGr8
author_rank: Super Contributor
timestamp: April 17, 2014, 11:14:10 pm
content: Photomultiplier tubes (a special type of vacuum tube) are still found in some spectroscopy instruments.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 17, 2014, 11:22:59 pm
content: Hi,Add X-ray tubes to your list.Jay_Diddy_B

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 18, 2014, 12:18:53 am
content: For some reason, display tubes are still very common in automotive.

author: c4757p
author_rank: Super Contributor
timestamp: April 18, 2014, 12:35:13 am
content: Quote from: NiHaoMike on April 18, 2014, 12:18:53 amCheap LCDs and older LCDs don't work well in extreme cold, and LEDs have sucked for longer than they have not sucked. VFDs are still very nice displays when you want something with a long life, functional under all conditions, and very visible, even though they're expensive and a pain in the ass to drive.Automotive electronics, particularly the less important bits like indication, seems to lag a bit, probably due to extensive testing and whatnot. My 14-year-old car has lots of incandescent indicators and circuits made from discrete BJTs - that wasn't even "state of the art" in the 1970s

author: SArepairman
author_rank: Frequent Contributor
timestamp: April 18, 2014, 01:06:31 am
content: oh yea I meant to dismiss display tubes. I have an old ass display tube right in front of me, it slipped my mind.I kind of have the appreciate the electron gun aimed at my face...anything else?so xray, photo multiplier,I was thinking more for in circuit properties, maybe used in some kind of hybrid electronics.... something like "best noise generator" ( i have NO idea im just pulling obscure machine names out of a hat ).. non transducer applications (if there is such a thing! philosophy )there are alot of sensors using tubes, like high vacuum measurement.http://en.wikipedia.org/wiki/Hot-filament_ionization_gaugeim sure there are other interesting ones too. I am interested in both circuit elements and world-circuit interface sensors. (but really can the distinction ever be made??)physics comes up with wacky tube things all the time I bet..

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 18, 2014, 01:20:49 am
content: ^ Probably because the alternative is poor over the temperature range (slow or malfunctioning LCDs) or unreliable (OLEDs are still relatively new and suffer burn-in).TWTs are still flown on satellites.IOTs (Inductive Output Tube I think..??) were a special type of amplifier for UHF TV service, which unfortunately isn't compatible with DTV. Apparently, the cavity amplifier approach has too much dispersion or something. Kind of funny because NTSC is moderately sensitive to phase and amplitude distortions already, but, not to the precision of, like, cycle-to-cycle errors, like DTV is. I guess.Magnetrons!Arguably, any kind of plasma device -- although I don't know if you'd really call a xenon arc lamp a "tube", in the sense of "vacuum tube", since they're in fact under high pressure. (Others, like metal halide or HPS lamps, may start at a low pressure, but generate lots of pressure once they heat up. LPS, mercury vapor (most fluos), neon and other types do run at low pressure.)As for common, bog standard, apples to apples, receiving tubes (triodes, pentodes and such), not so much -- there is absolutely no performance factor that, say, a 12AU7 beats a 2N3904 with.Meaning, gain, frequency response (transconductance divided by feedback capacitance is commonly used as a quality factor), noise figure and so on. Absolute current, voltage or power don't count, as those are selection / scaling parameters, not fundamental sorts of limits.There are some notable characteristics though. Few transistors have ever achieved such low feedback capacitance of pentodes (anode to control grid; compare with Crss for FETs, or collector capacitance for BJTs). Noteworthy challengers include this2SK241I found in a radio (Crss = 35fF typ. -- not sure how they achieved that, is it just basic lateral MOS that achieves such performance, or is it actually an internally cascode-strapped dual gate?), most any dual-gate device (that is, when they were still being made!), and modern PHEMTs and such, which offer ludicrous performance besides (80GHz+ fT -- the Gm/Crss factor is through the roof!).Because VDMOS transistors exhibit a quadratic Rds(on) vs. Vdss characteristic, they downright stink for unfairly high voltage ratings. I've seen MOSFETs rated for 2.5-4kV, in a single device, which are beaten handily by horizontal deflection tubes.It seems pretty reasonable devices are available now:http://ixapps.ixys.com/DataSheet/DS100280(IXTK-TX5N250).pdfso I can no longer say there is no single semiconductor device, commercially available, that's not better than a sweep tube!For comparison, the performance of something like EL519 or 6LQ6 is roughly equivalent to a MOSFET with Rds(on) = 40 ohms, Vdss = 6-8kV (for short duration peaks, in cutoff), Vgs(th) = -60V (but, this depends much more on plate voltage -- the plate resistance in these beam tetrodes is not insignificant, and Vg1 < -150V is required for full cutoff at the maximum voltage rating), and Gm = 30 mmho (oh, sorry, mS). The voltage gain is much lower (expect 100-200Vpp grid drive), but the capacitance is lower as well (~30pF Ciss), and fairly constant (whereas semiconductor capacitances vary strongly with voltage, especially the newest types). Silicon carbide MOSFETs are available today which similarly have reduced capacitance and voltage gain (typically, -2/+30V is suggested), with better Rds(on) vs. Vdss ratings.Among semi-special-purpose tubes, one could argue the case that they are better in certain figures also. A 7360 beam deflection tube is built to produce a sheet electron beam, which is deflected by two electrodes, to reach a split plate. If the sheet's electron density is constant (a nice sharp rectangular beam), the applied deflection voltage will be directly proportional to the difference in plate currents; and if the beam current can be scaled proportionally without affecting its geometry, an ideal two quadrant multiplier is had.The beam, of course, is not perfectly sharp, but tapers off on the edges. The middle remains pretty solid, so that -- indeed, a multiplier of excellent linearity, at fairly large signal level, is had.The semiconductor equivalent is the three-BJT diff amp (e.g., CA3028), which has variable "tail" current and a differential current output proportional to tanh(Vin) (plus various temperature coefficients and matching requirements). Linearizing diodes can be used to improve the linear range (typical of OTA circuits), but typically, a lot of work (including fine trimming, I guess) goes into making a stable, general purpose, bi-linear multiplier -- hence the AD633 still costs $5 in singles!The 7360 (and a few others) were usually used for SSB radio (mod/demod), since a single tube will get you AM-DSB-SC with a pretty good carrier null (-40dB). Three can be used (one at the bottom, two above, cascoded on the respective plates) for a double balanced mixer (compare to a Gilbert cell). SSB can be synthesized directly, using one pair and the phase-shift method (unfortunately, you need a perfect 90 degree phase shift on your audio, 500-3000Hz bandwidth say, plus the RF, to do this).Tim

author: david77
author_rank: Frequent Contributor
timestamp: April 18, 2014, 01:36:40 am
content: Do Geiger counters still use tubes as detection element or is there a newer type of sensor available?Though, I doubt you'd count a Geiger-Müller counting tube as a tube in the classical sense anyway, as they're not heated, just evacuated.

author: miguelvp
author_rank: Super Contributor
timestamp: April 18, 2014, 01:46:08 am
content: Scanning Electron Microscopes, that's as big as a vacuum tube can getBen Krasnow's DIY Scanning Electron Microscope:Ok, not modern by the standard that you can buy it, but modern as you can build it now

author: staxquad
author_rank: Frequent Contributor
timestamp: April 18, 2014, 04:32:05 am
content: Nixie tube watchmust be tech savvy to own one

author: daqq
author_rank: Super Contributor
timestamp: April 18, 2014, 06:16:58 am
content: QuoteThere are newer sensors available, but geiger tubes are still very popular being cheaper (most of the time) than other sensors.There are very few tube like devices in commercial stuff (aside from magnetrons in your microwave oven), but there are some parts of the more obscure stuff that use special tubes. The ones that were mentioned, plus:- the heart of cesium atomic clocks- spark gap protection (gas discharge tube) is arguably a tube-ish device (http://www.littelfuse.com/products/gas-discharge-tubes.aspx)- radar stuff (aside from the magnetron, there is a protection parthttp://www.tubecollector.org/1b38.htm)- some laser are arguably tube-ish devices

author: SeanB
author_rank: Super Contributor
timestamp: April 18, 2014, 08:46:31 am
content: Your CFL lamp has a vacuum tube inside. You can actually use them as diode valves over a limited range by simply only heating the one filament with 4V. You can generally draw up to 100mA with a reverse voltage of about 50V without too much reverse conduction. As a bonus it will light up with forward conduction.

author: G7PSK
author_rank: Super Contributor
timestamp: April 18, 2014, 08:54:25 am
content: Electron beam welder, some military electronics especially where they need to withstand large amounts of EMP high speed timing devices for atomic bombs used to be a vacuum tube device many probably still are.Nasa where they also need radiation hardened devices.http://news.sciencemag.org/physics/2012/05/return-vacuum-tube

author: Shock
author_rank: Super Contributor
timestamp: April 18, 2014, 11:08:13 am
content: Chess set?

author: SeanB
author_rank: Super Contributor
timestamp: April 18, 2014, 11:44:26 am
content: Flash tubes are an application of cold cathode vacuum devices, along with CCFL lights used to illuminate LCD displays.

author: FJV
author_rank: Regular Contributor
timestamp: April 18, 2014, 03:59:44 pm
content: http://www.darpa.mil/NewsEvents/Releases/2013/11/21.aspx

author: GreyWoolfe
author_rank: Unknown
timestamp: April 18, 2014, 05:51:29 pm
content: Tubes are still the preferred choice for Ham Radio amplifiers.

author: SArepairman
author_rank: Frequent Contributor
timestamp: April 18, 2014, 07:19:14 pm
content: Quote from: GreyWoolfe on April 18, 2014, 05:51:29 pmwhy

author: N2IXK
author_rank: Frequent Contributor
timestamp: April 18, 2014, 07:53:55 pm
content: Simplicity of design.Ease of repair/modification.Less sensitive to damage from overdrive or poor VSWR.Quote from: SArepairman on April 18, 2014, 07:19:14 pm

author: GreyWoolfe
author_rank: Unknown
timestamp: April 18, 2014, 09:20:20 pm
content: Quote from: SArepairman on April 18, 2014, 07:19:14 pmMost of the major players that sell amplifiers here in the US, sell tube amps for HF. There are some, notably Tokyo Hi-Power, Elecraft and Ameritron, that make solid state amps, but the majority of the amps available are tube. Alpha Amplifiers, the unquestioned big dog on the block, only offers tube amps. I know a lot of hams that have amps and everyone of them are tube. I am not aware of any company making VHF or UHF amplifiers using tubes, though, they are all solid state.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 19, 2014, 02:25:58 pm
content: LunarLink made tube 2m & 70cm Amplifiers till fairly recently,but the owner,Steve Powlishen passed away.I don't know if anybody is carrying on with the business.UK Linear in the UK also make them.

author: David Hess
author_rank: Super Contributor
timestamp: April 20, 2014, 12:41:20 am
content: They are handy where you need a rugged high impedance input stage like for an electrometer or power pass element in a high voltage power supply. There is a low power RF use as an ESD and lightning resistant RF amplifier.I think there is also an obscure use as a low forward voltage drop detector which would have been served by back diodes except they are gone as well.Space charge tubes can be used as electrometer amplifiers with only a 1.5 volt supply in portable equipment like radiation survey meters and of course any application which requires extreme radiation resistance.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 20, 2014, 12:54:25 am
content: I don't know how useful the electrometer types really were; your main concerns are offset voltage (and drift), which are better with a JFET. They did achieve comparable leakage currents though.6AL5 is still better than any schottky diode, at fractional mA currents. Frequency response is limited mainly by electrode inductance and capacitance (the datasheet claims resonance around 600MHz?).Tim