# Vacuum tubes **URL:** \ **Category:** Factual Questions\ **Created:** [April 7, 2003, 12:32pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040 "2003-04-07T12:32:37Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![justwannano](https://avatars.discourse-cdn.com/v4/letter/j/7ab992/32.png) [@justwannano](https://boards.straightdope.com/u/justwannano)\ **Post date:** [April 7, 2003, 5:08pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/21 "2003-04-07T17:08:09Z")
Some of us old timers still have our tube caddies. Not a very good selection though. ---
**Author:** ![Foolonthehill](https://avatars.discourse-cdn.com/v4/letter/f/e274bd/32.png) [@Foolonthehill](https://boards.straightdope.com/u/Foolonthehill)\ **Post date:** [April 7, 2003, 5:12pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/22 "2003-04-07T17:12:13Z")
Macintosh; the amplifier manufacturer, not the computer, still supply tubes ---
**Author:** ![Running\_with\_Scissors](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Running\_with\_Scissors](https://boards.straightdope.com/u/Running_with_Scissors)\ **Post date:** [April 7, 2003, 5:15pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/23 "2003-04-07T17:15:36Z")
Believe it or not, some Western Electric tubes are still being produced, on the same equipment that they were when they were in their heyday: [http://www.westernelectric.com/history.html](http://www.westernelectric.com/history.html) ---
**Author:** ![justwannano](https://avatars.discourse-cdn.com/v4/letter/j/7ab992/32.png) [@justwannano](https://boards.straightdope.com/u/justwannano)\ **Post date:** [April 7, 2003, 5:27pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/24 "2003-04-07T17:27:51Z")
Unless its some special radio,and your description,“white plastic radio”, tells me it isn’t its probably a 5 tube superhet. It has series filaments. the first number of the tube type is generally the fillament voltage. you’ll have a 50c5,a 35w4 a couple of 12 volt tubes and a 6 volt tube.sorry can’t remember the #s Add the numbers up and iyou will find it adds up to 109volts.Mighty close to the 110 volt ac line voltage. The 50c5 and 35w4 are the most common tubes to burn out. So if you can find those 2 tubes it’ll probably operate for years. ---
**Author:** ![Wikkit](https://avatars.discourse-cdn.com/v4/letter/w/c0e974/32.png) [@Wikkit](https://boards.straightdope.com/u/Wikkit)\ **Post date:** [April 7, 2003, 5:41pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/25 "2003-04-07T17:41:20Z")
> [@](#): > > \*Originally posted by Derleth \* > \*\*Can you still buy vacuum tubes used in old computers? If one wanted to recreate the first generation of computers, possibly build some new machines, would it be possible without making certain tubes from scratch? \*\* The Atanasoff-Berry Computer, the very first electronic digital computer, was re-created a few years ago (and is sitting about 100 feet from me right now). About 3/4 of the way down [this page](http://www.scl.ameslab.gov/Projects/ABC/Progress.html) you can see the vacuum tubes they used-- old ones, made in the 40s. So, they’re apparently still available somewhere. I could probably find out where they got them, if you really want to know. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [April 7, 2003, 5:51pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/26 "2003-04-07T17:51:11Z")
Wow. I seem to have stuck oil! Maybe I should go get that old radio? ---
**Author:** ![justwannano](https://avatars.discourse-cdn.com/v4/letter/j/7ab992/32.png) [@justwannano](https://boards.straightdope.com/u/justwannano)\ **Post date:** [April 7, 2003, 5:53pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/27 "2003-04-07T17:53:49Z")
Red faced embarrased grin Oops forgot to add the 6 volt tube Thats 115 volts folks ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [April 7, 2003, 6:02pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/28 "2003-04-07T18:02:49Z")
Here’s a Pentium 4 motherboard with an onboard vacuum tube amp: [http://www.aopen.com/products/mb/ax4b-533tube.htm](http://www.aopen.com/products/mb/ax4b-533tube.htm) I really don’t see the point myself. ---
**Author:** ![DougC](https://avatars.discourse-cdn.com/v4/letter/d/7feea3/32.png) [@DougC](https://boards.straightdope.com/u/DougC)\ **Post date:** [April 7, 2003, 6:11pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/29 "2003-04-07T18:11:24Z")
- - - You can still get most standard vacuum tubes online, some NOS, others just-plain-new. There are still companies making tubes as well as tube audio and radio equipment. - Tube audio equipment is expensive, but I’m not sure quite why. After looking online for quite a while, the smallest stereo tube amp kit I have been able to find anywhere is a stereo 16W available from a couple different retailers for the same price–$140 (-a transistor amp the same power might cost you $15): [http://www.audioxpress.com/bksprods/kits/KS5-1.htm](http://www.audioxpress.com/bksprods/kits/KS5-1.htm) It uses 4 common tubes that cost $10 each, plus what looks like perhaps $20? at most of other common electronic parts-??? Not a lot of competition in the small tube-amp market, I guess. Electro-geeks have told me it’s much cheaper to find a free schematic and just buy/make all the parts yourself. At least one of the transformers has an odd tapped winding. ~ ---
**Author:** ![Zenster](https://avatars.discourse-cdn.com/v4/letter/z/cdc98d/32.png) [@Zenster](https://boards.straightdope.com/u/Zenster)\ **Post date:** [April 7, 2003, 7:11pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/30 "2003-04-07T19:11:03Z")
> [@](#): > > \*Originally posted by Joey G \* > \*\*That sure is a big amplifier. 😉 \*\* Hades! Some of the semiconductor reactors I’ve operated used 10-15 KW RF power amplifiers (read transmitters). Enough to fry you pretty quickly. (Actually, it attacks nerve endings and fine structures like your eyes and brain.) ---
**Author:** ![Zenster](https://avatars.discourse-cdn.com/v4/letter/z/cdc98d/32.png) [@Zenster](https://boards.straightdope.com/u/Zenster)\ **Post date:** [April 7, 2003, 7:17pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/31 "2003-04-07T19:17:29Z")
And just for the sake of technicality, lots of “vacuum” tubes do not have a vacuum in them at all. They are intentionally back-filled with a partial pressure of argon or other inert gases in order to enhance electron transport between the anode and cathode. This partial atmosphere also extends the tube’s lifetime by decellerating the leak-back rate of ambient atmosphere through its feedthrough sealing points. ---
**Author:** ![Berkut](https://avatars.discourse-cdn.com/v4/letter/b/a88e57/32.png) [@Berkut](https://boards.straightdope.com/u/Berkut)\ **Post date:** [April 8, 2003, 10:49pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/32 "2003-04-08T22:49:20Z")
> [@](#): > > _Originally posted by Joey G_ > **That sure is a big amplifier.** > [@](#): > > \*Originally posted by Zenster \* > \*\*Hades! Some of the semiconductor reactors I’ve operated used 10-15 KW RF power amplifiers \*\* I was speaking more of its intended use, hence the 😉 smiley. 😉 ---
**Author:** ![YWalker](https://avatars.discourse-cdn.com/v4/letter/y/6f9a4e/32.png) [@YWalker](https://boards.straightdope.com/u/YWalker)\ **Post date:** [April 9, 2003, 12:30am UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/33 "2003-04-09T00:30:28Z")
These guys make expensive tube stereo equipment. They are a few miles from my home. [http://www.caryaudio.com/](http://www.caryaudio.com/) One of the latest things in guitar amps is the use of software to emulate various amp sounds. You buy 1 amp and it can sound like many different types of amps including tube amps. ---
**Author:** ![Contrabass](https://avatars.discourse-cdn.com/v4/letter/c/cc9497/32.png) [@Contrabass](https://boards.straightdope.com/u/Contrabass)\ **Post date:** [April 9, 2003, 2:05am UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/34 "2003-04-09T02:05:05Z")
> [@](#): > > \*Originally posted by Crafter\_Man \* > \*\*I’m pretty sure tubes are still used in radio and TV transmitters. While solid state has its advantages, so far no one has come up with a way of producing thousands of watts of RF energy using transistors… > > Last I heard, regular ‘ol vacuum tubes are still being made in Russia and China. \*\* Here are the Russian brand ones: [Sovtek](http://www.turnstyle.com/nsc/catalog.asp?category=tubeshop) or [Sovtek](http://www.sovtek.com/) I worked at a guitar amp repair place the summer after graduating High School, before going to college. That was one replacement brand. Indeed, musicians like tube amps because of their clipping characteristics when you over drive them. You have the pre-amp put out more power than the power amp is meant to take as input (for clean sound reproduction). The signal clips, and the distortion sounds good. When you do this to an transistor, it sounds awful… Now, the notion of tube amps sounding more accurate in a stereo than transistors is a whole 'nother thread… (Tubes sound “warmer”, sure, but not more accurate. There’s a difference…) –ContraBass ---
**Author:** ![Zenster](https://avatars.discourse-cdn.com/v4/letter/z/cdc98d/32.png) [@Zenster](https://boards.straightdope.com/u/Zenster)\ **Post date:** [April 9, 2003, 6:17am UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/35 "2003-04-09T06:17:43Z")
Actually, tubes go through what is known as ‘roll off,’ which is very different from what transistors do, which is ‘clipping.’ Roll off is a gradual degradation in the tube’s ability to pass signals at the top end of its performance envelope. Most of the audio frequencies are equally dampened by this roll off in performance. When a transistor ‘clips’ an overdriven signal it lops off the top part of any sine waves passing through it and delivers something more akin to a square wave. Square waves have annoyingly harsh timbre characteristics due to the abrupt changes in attack envelope and overall wave shape. Natural sounds tend to be sine or sawtooth waveforms. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [April 9, 2003, 12:23pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/36 "2003-04-09T12:23:38Z")
> [@](#): > > \*Originally posted by Zenster \* > \*\*And just for the sake of technicality, lots of “vacuum” tubes do not have a vacuum in them at all. They are intentionally back-filled with a partial pressure of argon or other inert gases in order to enhance electron transport between the anode and cathode. This partial atmosphere also extends the tube’s lifetime by decellerating the leak-back rate of ambient atmosphere through its feedthrough sealing points. \*\* This is somewhat OT, but I’m curious: why would filling it with argon decrease the leak rate? Let’s say I fill a tube with 101 kPa of argon. Atmospheric air is around 101 kPa. One would _think_ that these should “cancel.” But what about Dalton’s Law of partial pressures? Wouldn’t Dalton’s Law say that: - argon would flow _out_ because there’s a large pressure difference of argon - nitrogen would flow _in_ because there’s a large pressure difference of nitrogen - oxygen would flow _in_ because there’s a large pressure difference of oxygen - etc. I’m no physicist, so I could be way off base here… ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [April 9, 2003, 2:23pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/37 "2003-04-09T14:23:35Z")
**Crafter\_Man** : The presence of nitrogen and/or argon does two things: 1. Allows convection cooling of the filament. 2. Reduces evaporation of tungsten from the filament. **Zenster** ’s claims of enhanced “electron transport between the anode and cathode” and reduced “leak-back rate of ambient atmosphere” are specious. That is, they sound plausible but are actually BS. ---
**Author:** ![racer72](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/racer72/32/3075_2.png) [@racer72](https://boards.straightdope.com/u/racer72)\ **Post date:** [April 9, 2003, 3:44pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/38 "2003-04-09T15:44:27Z")
I still have a vacuum tube testing manual from the early 70’s. It shows how to test each type of tube using a VTVM (Vacuum Tube VoltMeter) and an oscilliscope. I tried to test some old tubes a few years ago but instead of a VTVM I tried my digital Fluke meter. The Fluke would not work. I ended selling a large box of questionable quality vacuum tubes on Ebay for $95. In my line of work testing new commercial aircraft, we still have tests that require the use of old style analog meters. ---
**Author:** ![DougC](https://avatars.discourse-cdn.com/v4/letter/d/7feea3/32.png) [@DougC](https://boards.straightdope.com/u/DougC)\ **Post date:** [April 10, 2003, 11:03pm UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/39 "2003-04-10T23:03:01Z")
- - - Since we’re all here, I am mildly curious as to building a tube amp, but all the kits I find seem highly overpriced. I can find free schematics for smaller amps on the web and I can locate sources for all the parts pretty easily, except one: the transformer(s). - I had some electronics courses way back in high school and know a few basic facts about transformers, but not anything about in-depth matters such as selecting core materials. The only [good] electronics store around does carry unwound cores of different sizes and materials, but they’re all smaller than what I see used on tube amplifiers, and the ones at the store seem to be types optimized for RF use–the material rated for the lowest frequency available in the (rather thick) core applications guidebook the store had on hand was rated down to only 50Khz. The book was filled with undecipherable charts, and it’s safe to bet that I don’t know anything else about transformer design. I don’t yet know what cores tube-amp builders use. - So I know that I could cut out thin sheet steel pieces and varnish them and (somehow) fasten them together into a core shape, and I could wind the core with appropriate windings, but I wouldn’t have a clue as to if the transformer was too big here or too small there. What is the worst that might happen with doing this? If I made the core hollow, could I blow air through it to help cool it? I’m guessing as far as overall physical size goes, smaller would give better electrical efficiency but more heat, and I’d probably build mine too big rather than too small, at least the first time around… Aside from smoke, are there any tell-tale signs that a given transformer is being overdriven? Are there any tests I could do with a simple multimeter? ~ ---
**Author:** ![Zenster](https://avatars.discourse-cdn.com/v4/letter/z/cdc98d/32.png) [@Zenster](https://boards.straightdope.com/u/Zenster)\ **Post date:** [April 11, 2003, 7:18am UTC](https://boards.straightdope.com/t/vacuum-tubes/167040/40 "2003-04-11T07:18:44Z")
> [@](#): > > \*Originally posted by Desmostylus \* > \*\ ***Crafter\_Man** : The presence of nitrogen and/or argon does two things: > > 1. Allows convection cooling of the filament. > 2. Reduces evaporation of tungsten from the filament. > > **Zenster** ’s claims of enhanced “electron transport between the anode and cathode” and reduced “leak-back rate of ambient atmosphere” are specious. That is, they sound plausible but are actually BS. \*\* Thank you for clarifying on some things I was taught by my electronics teacher in high school. I will say that the _effects_ of ambient atmosphere leaking _in_ should be reduced by the presence of another gas already occupying the tube’s envelope. [Previous page](https://boards.straightdope.com/t/vacuum-tubes/167040.md?page=1) [Next page](https://boards.straightdope.com/t/vacuum-tubes/167040.md?page=3)