There was a rumour doing the rounts about 50 years ago that at least one manufacturer used water-soluble markings on the valves. The idea was that old valves could not be washed and cleaned up and then sold as new ones. Certianly soem markigns do come off very easily. -tony

Depends on the gas, among other things. Hydrogen, for exmaple, diffuses annoyingly fast through pretty much anything. (Annoyingly fast for those who want to contain it, at least.) I suspect it also depends on how much getter function is left. The getter's whole point is to capture stray bits of gas; as long as it lasts, it'll be scavenging up any stray molecules that do find their way in. I suspect internal outgassing is more significant than diffusion through the body of the thing, in most cases, though. /~\ The ASCII Mouse \ / Ribbon Campaign X Against HTML mouse at rodents-montreal.org / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B

At 6:30 PM -0700 3/13/13, Fred Cisin wrote: I'm not going to literally "toss" them into the Attic. :-) As for dumping them into the toolbox, I wasn't the one that placed them in there, so I really can't speak to that. :-) Zane -- | Zane H. Healy | UNIX Systems Administrator | | healyzh at aracnet.com | OpenVMS Enthusiast | | | Photographer | +----------------------------------+----------------------------+ | My flickr Photostream | | http://www.flickr.com/photos/33848088 at N03/ | | My Photography Website | | http://www.zanesphotography.com |

Not any more. Semiconductors have taken over that field almost completely. It is far better (reliability, cost, and efficiency) to use an army of silicon over one or two vacuum tubes. The big manufacturers of superpower tubes, like CPI (Eimac), do most of their business fulfilling replacement for existing sockets. No, the metal tubes were originally a cost savings design. The US military did not start using them until 1938-ish, yet metal tubes were introduced a few years earlier. There are dozens of civilian radios that used them before the military adopted them. -- Will

This is true; they are far more robust than modern semiconductors. Substantially less. When I was fooling around with glassfets in the '70s, I usually used B+ voltages anywhere between about 80V and 150V. Then I spoke with a guitar tech about using 12AX7s, I think it was, in guitar effects, and was wondering where they got the high voltage. He told me B+ in such circuits is, IIRC, 12V. It makes sense - power delivered is not really a consideration in such things - but it was a bit of a surprise to me.... Pretty much anything that can deliver hundreds-to-thousands of watts can be quite deadly. (Even modern computer power supplies - anything that can push 100A at 3.3V definitely deserves an energy hazard warning label! I've heard stories - first-hand, mind you, as in told by the person bearing the burn scars - of energy hazard accidents that make me wince from empathy...and make me very glad I'm not in a position to tell such stories myself. Okay, probably not truly _deadly_, but certainly pretty harsh.) /~\ The ASCII Mouse \ / Ribbon Campaign X Against HTML mouse at rodents-montreal.org / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B

So can 120V...all it needs to do is push enough current through you to convulse the wrong muscles and/or stop your heart. The only reason 3.3V is safe in this respect is that it requires very good contact to push much current through a human body, better than is reasonably foreseeable. Possibly better than is possible; I don't know the danger threshold for current, nor the resistivity of human flesh. 120V can do this; if contact is good - eg, if your skin is wet with dirty (ie, conductive) water - even lower voltages (48V? 24V? please don't any of you find out in person!) can push enough current to be dangerous. But a low enough voltage is safe because it can't push hazardous current levels even with really good contact. And the "other hand in your back pocket" rule helps because - provided the rest of you is insulated, especially your feet - it means that even if you get a bad jolt, it's not going to go near anything really dangerous (most notably your heart). My father used to test 9V batteries by touching the tip of his tongue across the terminals; this provides excellent contact (by human-body standards), but the current isn't going to go anywhere but through the tonguetip. Of course, as you found... ...shocking your heart into fibrillation isn't the only hazard. It's just one of the few that's directly and immediately lethal. Actually, the human body is pretty robust. Even if you get a good stiff jolt right down one arm and up the other - or between an arm and a leg - right past your heart, you _probably_ will survive. People regularly survive direct lightning strikes.... It's just that when the event being risked carries a cost that high, even what would in other contexts be a tiny chance is worth taking significant measures to avoid. In lots of contexts a 10% chance is small enough to be ignored. In lots more contexts, 1% is. But I wouldn't ignore either one when what I'm risking is stopping my heart. Not unless it's the best way out of something even more likely to be lethal, and such cases are very rare. /~\ The ASCII Mouse \ / Ribbon Campaign X Against HTML mouse at rodents-montreal.org / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B

A low anode volatage is likely to cause distortion at quire moderate signal nlevels, which might be an advantage for that application. Certianly you cna run some, if not, most small signal valves at low anode votlages 912V or 24V). Power tyoes are non-starter, although I have heard of people using TV line output valves ('sweep tubes'?) with a 12V anode voltage to drive headphones. Philips made a few 12V anode types for car radios (with a single transitor as the audio outpu stage) that were known to be selected versions of more nornma, types (ECH83 -- ECH81 nad EBF83 -- EBF89 IIRC). Other companies made similar valves, including soem where you applied a +ve voltagr to the first grid to act as an acceleerator. -tony

On 03/14/2013 03:16 PM, Tony Duell wrote: Although there were some low-voltage space-charge tubes for automotive use, just about every auto radio that I've ever seen that uses those throws in the towel and uses a good old power transistor for the final audio stage. I recall building a code-practice oscillator that used nothing more than a 6.2VAC filament transformer for its power supply. The tube used, IIRC, was a 6SL7 dual triode. It did make use of an interstage transformer for the audio feedback loop and drove a pair of high-impedance headphones for a somewhat audible tone. Generally speaking, however, it makes design a lot easier if you employ a real high-voltage plate supply. As far as audio goes, it's my impression that solid-state amplifiers tend to use a lot more negative feedback than did even the ultra-linear tube versions. But then there are those who believe that any feedback is a crime against nature and run class A power triodes with zero feedback for a couple of watts of power. --Chuck

Yeah...that was the point. -- Will

On Mar 15, 2013, at 8:55 AM, geneb <geneb at deltasoft.com> wrote: They were pretty gimmicky, actually. You can't get a whole lot of gain out of a single 12AX7 (especially if you're using it to amplify both channels, so you only get one triode per channel), so essentially they were using the tube to distort the sound. You'd probably get much better audio quality with a high-end, low-noise 24-bit sound card running into a proper tube preamp. They were kinda cool, I guess, but I think the actual benefit was much more along the lines of window dressing than actual audio quality. - Dave

Absolutely. There were 12V-anode valves for the frequency changer and IF stages. These did not have 'space charge grids' normally. I came acorss one audio driver valve that did ahve a space charge grid (12K5 or something?) but it didn't drive the speaker direcrily. It drove a (germanium) power transsitor. Of course older cer radios were fully voalves (includign the sudio output stage), but they had a vibrator and setp-up transformer to get about 250V fro mteh car battery. Anyone else remeember the 0XZ4 rectifier? Common is such car radios. A number of UK magazies published 'experiement@ projects i nthe 1950s that powered the vlave heaters from a mains transformer but got the anode votlage my half-wave rectifying the mains -- no isolation. And soem fo those projects used headphoens. A little bit of isulation breakdown and you could find you'd made a very effective electric chair... Sure. It's not hard to do. -tony

On 3/15/2013 4:05 PM, Chuck Guzis wrote: The radio in my Nash Metropolitan uses a vibrator rectifier. It was a lost cause and when I rebuilt it I replaced the rectifier with a solid state replacement. On the subject of tube radios, I picked up an RCA Victor BP-10 awhile back; this is a portable from about 1940 and it's actually pretty darn tiny for a tube-based unit. (And it runs off a 63.5V B battery (#467) and one D-sized 1.5V battery. Amazingly you can still buy the 63.5V batteries new...). Anyway, I bring it up because aside from its small form factor it has one other attribute I've never seen in a tube radio -- it starts playing almost immediately (within a second) of turning it on and the tubes never seem to get warm at all. All the other tube units I've ever seen take 10-20 seconds to warm up first. Makes me wonder a) what's special about this unit and b) why other units didn't do the same -- seems like a pretty useful feature. Any ideas? Josh

Most AM portable sets obver here used 4 vavles. The signal valves (frequency changer, IF amplfier, detector%1st audio) had 1.5V filamanet,s originally at 50mA eachm, later 25mA. The otuput volve had 2 filamnet sections that were connected. For batter-only sets all 5 filament sections were connected in parellel and powered by a 1.5V battery (yes, often several cells in parallel, so 'battery' is correct). But we also had battery/mains sets. These normally put the 5 filament sections in series and used a 75.V (!) LT battery. For mains, the HT (90V) came form eitehr amins transofrmer and rectifier or a dropping resistor and half-wave rectifier straight off the mains (no isolation). The heater chain was then fed form thsi DC HT line viaa fat droppign resisotr. Not exactly efficient, but... One trap for the unwary is that when you put hte valve filaments in series, the current throug them also includes the anode current. Thereofre the volve at the earthy end of the chain is goig nto be carying rather more filament current than it should do, since it will also have to carry the anode current of all teh valves above it. The crue was to fit shut reissotrs across the filaments to get the currents right again. I seem to rememrb that if you ran a DL96 or 3V4 or... with the filimant sections in seires you had to shunt the more -ve one (resisotr from the filament tap to the -ve side fo the filament) due to the anode current of this valve alone. -tony

On 3/15/2013 11:02 PM, Brent Hilpert wrote: I allways thought that the VFD tube layout would have made a NOR gate tube had that idea been developed in the 1950's. Ben

On 03/15/2013 09:28 PM, Josh Dersch wrote: Battery radios were like that--since there was no indirectly-heated cathode, it's ready to go as soon as the filament reaches temperature. About the smallest vacuum-tube radio that I remember owning was the Motorola Pixie. The Parrot was smaller, however: http://www.radiolaguy.com/Showcase/PortableRadios/subminiature.htm The funny thing was that for my first transistor experiments, I used submini tube sockets instead of harder-to-get transistor sockets. I used pick up surplus computer boards (I think they were military) that had 6 submini dual-triodes (usually) on them, in clips running on either size of the PCB in the middle. They were actually pretty useful in HF circuits. --Chuck

I meant 0Z4, of course I've never come across that one. The 0Z4 was not common in the UK, very few car radios used it, too. One of my vavled car radios uses a non-synchronous (primary side only) vibrator and a biphase metal rectifier (presumably selenium) for the HT supply. I can't rememebr what my other vavled car radio uses. -tony