Another weird item from my clear-out - tiny thermionic valves ! - Page 1
Forum section: electronics / general

author: Fraser
author_rank: Super Contributor
timestamp: April 14, 2016, 06:17:00 pm
content: During my current clear-out of electronics and test equipment I have stumbled upon all manner of 'stuff' that I had completely forgotten about. Its like Christmas every dayAfter ferreting through a box or receiver related spare parts I found some miniature thermionic valves that I thought I would share with the forum.When you mention thermionic valves to people they often think of the old 'Bottle' valves or later mini valves that resided inside vintage radios and televisions. What some people do not know is that thermionic valves were miniaturised for use in more modern radio equipment that needed their unique properties. Thermionic valves are very rugged devices in terms of overload performance and they are ideal in some military or high signal level applications.If I recall correctly the valves that you see on this post were spares for a Watkins Johnson professional EMC receiver that I once owned. They were used in the receivers front end due to superb overload characteristics.these miniaturised thermionic valves are called Nuvistors and, as can be seen, they are nice and compact. They still obey the laws of physics though so contain all the elements normally found in a full size thermionic valve. Precision engineering was required to construct them. Another name used to describe such miniaturised thermionic valves is "Acorn Valves". When looking at them, you can see why.Note the dumpy little valve with two pin connection on the bottom. It comes in its own anti silver tarnish bag ! I suspect these components were not cheap to buy.What to do with them now ? No idea. eBay maybe. If you need them PM me and we can discussPictures follow:

author: Fraser
author_rank: Super Contributor
timestamp: April 14, 2016, 06:20:51 pm
content: More pics

author: rsjsouza
author_rank: Super Contributor
timestamp: April 14, 2016, 06:39:15 pm
content: Beautiful specimens, Fraser; I always had a soft spot for vaccuum tubes (I have a small collection here).The 7077 is really well spec'd and can surely survive a nuclear blast.

author: SeanB
author_rank: Super Contributor
timestamp: April 14, 2016, 07:01:43 pm
content: I think you will have a flood of requests for the Nuvistors from Tek scope owners looking for spares for the older tube ones.

author: Ian.M
author_rank: Super Contributor
timestamp: April 14, 2016, 07:03:00 pm
content: I'm interested in the 6CW4 Nuvistors as spares for my Dynamco D7100/1X2/1Y2 scope. It would be nice to get the input DC offset back in spec and the drift down a bit!It still works for its living as my 'daily driver' CRO, so its not a museum exhibit or part of a collection.See:http://www.microchip.com/forums/m633344-p5.aspx#635093

author: Fraser
author_rank: Super Contributor
timestamp: April 14, 2016, 07:18:41 pm
content: @SeanBThanks, I had not realised that they were deployed in TEK and HP kit. Logical though as they were state of the art in their dayTo keep this thread interesting I have dug out the other unrelated thermionic valves that were in the same box as the Nuvistors.I have done a quick line up showing miniaturisation of the technology. There are some common sizes missing though as examples of tose will be hiding in the garage.With regard to the thermionic valves pictured in the following images, I cannot recall where they came from but I obviously kept them as curios. The last valve pictured is a lovely talking piece, it has its own custom holder and special socket. It may have been from a merchant ships RADAR. Not certain.Enjoy the pics

author: Fraser
author_rank: Super Contributor
timestamp: April 14, 2016, 07:21:29 pm
content: Weird valve with its own custom holder and socket........ Not exactly miniature but interesting none the less

author: SeanB
author_rank: Super Contributor
timestamp: April 14, 2016, 07:29:32 pm
content: Early airborne Radar klystron I think. I remember reading that the tubes were designed so they could be pulled out to be destroyed in case of the aircraft going down, so the technology did not fall into the wrong hands. Seeing as it was likely made late 1944 it would be a good museum piece if somebody can identify the set it was used in, You might want to send the pictures to somebody at Bletchly park and see if they recognise it.

author: Fraser
author_rank: Super Contributor
timestamp: April 14, 2016, 07:35:38 pm
content: I am receiving requests to purchase the Nuvistors. I had not expected that to be honest as I did not realise they were used in test kit.I will be totally fair in the dispersion of the Nuvistors if I sell them. All the boxed valves are brand new old stock and were procured from Watkins Johnson so will be of high spec when supplied new. There is one unboxed 7587 valve that may be seen to have a slightly discoloured underside. I am assuming this one is a good but used spare.Please continue to submit expressions of interest and I will see what I can do to satisfy your needs in a fair and reasonable manner.I have the following 'stock'RCA 6CW4 Qty 4 NOS in boxRCA 7586 Qty 2 NOS in boxRCA 7587 Qty 2 NOS in boxRCA 7587 Qty 1 Used spare? Hours not known.GE 7077 Qty 2 NOS in individual boxesFeeling bit surprised to be honest, I posted about these just to prove that thermionic valves did get very small towards the end of their reign.

author: Fraser
author_rank: Super Contributor
timestamp: April 14, 2016, 07:44:21 pm
content: SeanB,It is marked up as Telefunken LG 3 and is Ex Luftwaffe according to what I have just read.The Radio Museum list it as well........http://www.radiomuseum.org/tubes/tube_lg3.htmlFraser

author: SeanB
author_rank: Super Contributor
timestamp: April 14, 2016, 07:50:21 pm
content: Some quick beverage money there Fraser, as I cannot mention the brew made from malted hops and barley on this forum without bringing up the infamous Fosters episode. Yes they are very sought after, both for scopes and for some older amateur radio equipment which uses them, and for which there is only a dwindling stock left.I quite like the Soviet made tubes, and the others made for use in hearing aids.The LG3 then is a fighter aircraft or bomber transciever power supply tube. Interesting in having a handle for fast on flight line swapping then.

author: Fraser
author_rank: Super Contributor
timestamp: April 14, 2016, 08:14:30 pm
content: @SeanB,A quick bit of googling has enlightened me about the world of Nuvistors. As you say, they are needed for vintage TEK and HP equipment but are also sought after by audiophiles ! The Nuvistors that I have were also used in audio pre-amplifiers and broadcast radio microphones.The gem in this pile of Nuvistors appears to be the GE JAN 7077. It is a 3Ghz Ceramic Planar Triode. NiceThe 7077's seem to sell for good money still.Fraser

author: med6753
author_rank: Super Contributor
timestamp: April 14, 2016, 10:28:51 pm
content: Quote from: SeanB on April 14, 2016, 07:01:43 pmYep, a lot of 500 series plug-in's used nuvistors. 1A2 plug-in is a good example.

author: Ian.M
author_rank: Super Contributor
timestamp: April 14, 2016, 10:33:13 pm
content: Many of the scope 'nuts' will need a pair of the Nuvistors, for both channels of a dual input scope - unless one's been unlucky enough to have one fail totally.

author: Fraser
author_rank: Super Contributor
timestamp: April 14, 2016, 11:22:34 pm
content: It is interesting to see my RCA Nuvistors are in pairs, within a single box, when some others of the same type appear to have been sold in singles. I am wondering whether these were used in a balanced amplifier configuration in the EMC receiver front end and so are a matched pair ? Sadly the service manual went with the receiver many years ago.This has been an interesting discovery and I enjoy hearing about the different deployments of this late valve technology. I will be rehoming these examples with people who actually have a use for them. They may also raise a few pennies for my hobby account.For those who have PM'd me, I will reply soon. Time for bed now.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: April 14, 2016, 11:33:17 pm
content: I just did a quick search on WJ surveillance receivers and may have identified the model for which my Nuvistors were spares as I owned one of these 901 receivers as well as a 911. CEI designed it and WJ bought CEI.http://watkins-johnson.terryo.org/CEI-Receivers/901-1.htmFraser

author: MrSlack
author_rank: Frequent Contributor
timestamp: April 15, 2016, 06:02:16 am
content: Pre SN 20000 Tek 453s bizarrely used nuvistors despite the rest of the device being otherwise entirely full of BJTs and FETs. I think someone was smoking something that day. Was rather annoying as I had to work out how vacuum tubes worked for that one which wasn't on my bucket list for sure.

author: LazyJack
author_rank: Frequent Contributor
timestamp: April 15, 2016, 06:10:04 am
content: The 150 MHz 454 also uses Nuvistors. However, the designers weren't smoking anything. If you look closely, these tubes are used, where later scopes would use FETs. They just didn't have proper FETs for those functions back then. The successor 454A I believe uses all semiconductors.

author: Codemonkey
author_rank: Regular Contributor
timestamp: April 15, 2016, 06:37:52 am
content: Fascinating stuff! I've seen small valves before (around AAA cell size in a handheld geiger counter), but never knew about those tiny things. If anyone has a dead one it would be great to see one carefully opened up and see its tiny guts!

author: MrSlack
author_rank: Frequent Contributor
timestamp: April 15, 2016, 08:02:40 am
content: Quote from: LazyJack on April 15, 2016, 06:10:04 amThat actually makes sense now. Smoking comment retracted

author: SL4P
author_rank: Super Contributor
timestamp: April 15, 2016, 08:20:11 am
content: Nuvistors were also used in the head preamplifiers (located close to the spinning transverse head assembly) in Ampex quadruplex 2-inch video recorders - and possibly some of their other pre-70s mil-spec recording technology.

author: rdl
author_rank: Super Contributor
timestamp: April 15, 2016, 09:10:09 am
content: Musical Fidelity has made high end stereo equipment using Nuvistors.http://www.musicalfidelity.com/products/nu-vista

author: JohnPen
author_rank: Regular Contributor
timestamp: April 15, 2016, 02:40:36 pm
content: My old Tek 453 used nuvistors but some had failed. They just seemed to get very hot and no longer functioned properly so I modified the circuit to use FETs instead for the TBs. I duplicated the Tek 453A cct. The Y amp front ends still work OK and remain Nuvistors.

author: German_EE
author_rank: Super Contributor
timestamp: April 15, 2016, 08:18:35 pm
content: When I was a kid I remember seeing inside my Aunt Martha's hearing aid. The electronics box was about the size of a packet of twenty cigarettes and it had two or three tiny valves in it, each about 20mm long and wire ended rather than fitted into a socket. Most of the box was filled by the battery which must have been at least 40V.

author: daqq
author_rank: Super Contributor
timestamp: April 15, 2016, 09:10:14 pm
content: Thanks for the uploads! They are cute

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 15, 2016, 09:59:46 pm
content: Thanks for a trip down memory lane.I always thought that the term "acorn tubes" was reserved for the glass envelope tubes a little over a centimeter in diameter which where sealed around radial pins on a shelf around the lower half of the tube. Nuvistors were a still smaller package, originally proprietary to RCA. While Nuvistors were used in some high end gear, they also made it into television receivers during some of the last gasps of thermionics in that market. Probably reached their highest volume there. Thermionics made it well into the 1970s as the high voltage rectifier.

author: wkb
author_rank: Super Contributor
timestamp: April 16, 2016, 08:41:11 pm
content: Quote from: German_EE on April 15, 2016, 08:18:35 pmYep, and I even have a couple of these tiny valves somehere (...). A quick dig in the garage proved fruitless but I'll try to find them. And post a photo here of course.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 17, 2016, 12:14:17 am
content: I'd be rather interested in those 7077s, though by the sound of it I'm too late already.Tim

author: med6753
author_rank: Super Contributor
timestamp: April 17, 2016, 02:08:12 pm
content: Quote from: CatalinaWOW on April 15, 2016, 09:59:46 pmHere is a description of acorn tubes:https://en.wikipedia.org/wiki/Acorn_tube

author: Fraser
author_rank: Super Contributor
timestamp: April 17, 2016, 03:44:42 pm
content: I stand corrected on the Acorn valves. I never delved into their exact shape before.Fraser

author: richfiles
author_rank: Regular Contributor
timestamp: April 24, 2016, 06:54:50 am
content: Boy, those sure are beautiful little things!Makes you wonder where thermionic tech might have eventually led, had the transistor and it's derivatives not displaced it.

author: Ian.M
author_rank: Super Contributor
timestamp: April 24, 2016, 07:29:55 am
content: Probably to low voltage cold cathode ceramic cased hybrids with similar complexity and size to a SSI IC in a CERDIP package