Tube pinout problems - Page 1
Forum section: electronics / beginners

author: Algojervia
author_rank: Unknown
timestamp: October 28, 2016, 04:50:46 pm
content: Hello everyone!I'm trying to make a circuit diagram looking at a signal generator I found the other day. The first tube I looked at was a Mullard EL41 and a visual inspection seems to conform the pinout based on what I could find on the net. However this means that the cathode of the EL41 is unconnected (clean contact, has never been connected) witch goes against the very little I know about vacuum tubes. Is it a valid configuration to leave the cathode floating or it is a sign that I made a mistake?Also the next tube is a Mullard EF40 and every document I can find gives this pin configuration:1 h2 a3 ic4 g35 g16 g27 k,s8 hBut my visual inspection gives me this1 h2 a3 g14 k5 g26 a7 g38 hI have also confirmed that 2 and 6 are connected with the meter. The markings on the tube are very clear so that's not it.Does anyone have any experiences that can explain this or are vacuum tube just plain old magic.//A

author: danadak
author_rank: Super Contributor
timestamp: October 28, 2016, 11:01:38 pm
content: Here are the connections for the EL41 -http://www.r-type.org/pdfs/el41.pdfRegards, Dana.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 28, 2016, 11:09:10 pm
content: You're counting clockwise from the key, as viewed from the bottom, right? (Unless some European tubes went backwards, I don't know?)Tim

author: singapol
author_rank: Frequent Contributor
timestamp: October 29, 2016, 02:01:00 am
content: Welcome Algojervia,I guess you are new to tubes/valves and circuits. Datasheet pinout diagrams are drawnlooking from bottom up clockwise starting from notch unless stated otherwise (when viewed from the top). If you are looking from the top as in a pcb assembly then it will be counterclockwise for pin identification.EF41 and EF40 have different pinouts!Beware..look at the respective datasheet I linked. They are not identical or same. You are correct if your are saying pin 2 and 6 of EF41 is physically connected as seen in datasheetbut not EF40! There are 2 no connect pins on EF41 vs 1 pin only on EF40 not to mention the various signal pins. Yes it would seem cathode or K a is floating but so is anode and grid 1,2,3 but that's how a tube is. as depending on design these elements are separated by space..see their physical construction. A good source of tube info can be found at Pete Millet'stubebooks.org - Vintage info from the age of vacuum tubeswww.tubebooks.org/http://www.jogis-roehrenbude.de/Roehren-Geschichtliches/Behoerden/EF410/EF41.pdfhttp://www.mif.pg.gda.pl/homepages/frank/sheets/046/e/EF40.pdfIf a tube is marked EF40 and pin2 and 6 is connected then it is actually a EF41 or faulty?, such thing happens as sellers don't know enough about tubes and just want to sell thus making a bad name for themselves and angry /frustrated customers who do not know why their circuits fail. Another thing since EF40 is listed as A.F. (audio frequency) pentode it is very like sellers who have EF41 remark them as EF40 but EF41 is variable mu pentode for radio frequency use which does not amplify audio signals linearly.Beware again.

author: Algojervia
author_rank: Unknown
timestamp: October 29, 2016, 06:52:31 am
content: Thanks for your reply's. I have the documentation you both linked too and I understand how the pin numbering are arranged. (I have googled it!) But indeed it seems i made that mistake regarding EF40 when i listed the pins.First of all I seem to have misunderstood the i.c. label, in my mind it became not connected. On EL41 pin 3 called i.c. is connected to pin 7 and since pin 3 is connected it solves that mystery for me.However, I can't find any information in the documentation on what the i.c. pin are connected to?Quote from: singapol on October 29, 2016, 02:01:00 amI think I was unclear, I meant that the cathode pin where only connected to the socket and no connection was made to the cathode socket pin to the rest of the circuit. I do understand that the parts are separated inside the tube by vacuum.I have already done the rectifier part that uses a 5Y3 and have no problems understanding the principle since it's a simple dual diode so I do know some of the basics at least.I had assumed that the anode would always be the outer most active layer but it appears that on the EF41 the beam suppressor is a cylinder fence encasing everything else. Given that the pinout matches that of the documentation.Also I know about the getter and the black surface coating on the glass, however inside the unit there are two EF42. One marked Mullard as the rest of the tubes and one that has been replaced by one marked Philiphs. The older Mullard tube has the blackish top from the getter like the other ones but it also have an even silver coating that I believe might be from the anode. Is that a bad sign?//A

author: singapol
author_rank: Frequent Contributor
timestamp: October 30, 2016, 03:19:17 am
content: QuoteWhether it's black or silver it's normal. The silver splash inside the tube is the last process in the vacuum processby burning off ( normally a momentary application of high voltage to burn off an material deposited in a cup structure to remove any gas residue within the tube. This silver splash is the result of vapourising of this elementjust like a blood splash from a gunshot wound.

author: Algojervia
author_rank: Unknown
timestamp: October 30, 2016, 05:41:07 am
content: Ah yes but this is something else. The tube has the normal getter spot but there is another coating that probably can't be from the getter. But after lots of googling I can't find a single picture of a tube with a similar coating so I'm not surprised you didn't get what I meant. I have attached a picture to clarify.

author: Molenaar
author_rank: Regular Contributor
timestamp: October 31, 2016, 08:23:40 pm
content: As far as I know this is not abnormal and the tube should be fine.

author: TimFox
author_rank: Super Contributor
timestamp: October 31, 2016, 08:44:04 pm
content: On a vacuum tube connection diagram, "i.c." means "internal connection, do not use this socket pin for other connections".

author: singapol
author_rank: Frequent Contributor
timestamp: November 01, 2016, 02:29:40 am
content: Quote from: Algojervia on October 30, 2016, 05:41:07 amI believe you are an audiophile or an audiopfool in eevblog so am I? I offer you evidence that the Mullard branded tube in the middle is a genuine product MADE by Mullard in British Empire.In the glory days of the vacuum tube each manufacturer will try to better it's competitors notably RCA of America. The 2 other tubes flanking it are imports from foreign OEM possibly eastern europe by Mullard. Costs and profit margin rules so no getter at the middle of tube saving 1 extra production process. Even it is labeled as foreign made. Hope this clears your confusion.See the colour photo here: Mullard ef42:http://www.r-type.org/exhib/aab0167.htmand datasheet mullard ef42 photo:http://www.r-type.org/pdfs/ef42.pdfSome history of Mullard- From this :http://www.effectrode.com/vintage-mullard-yellow-print-tubes-white-print-tubes/QuoteThe "defect" in question you pointed out:http://www.audiotubes.com/nos.htmQuote

author: Algojervia
author_rank: Unknown
timestamp: November 01, 2016, 11:37:09 pm
content: Quote from: TimFox on October 31, 2016, 08:44:04 pmAh thank you then I understand. It was however relevant since the circuit I'm using connect to the cathode via the I.C pin.Quote from: singapol on November 01, 2016, 02:29:40 amActually not, it is even a bit of the opposite, that the focus on audio when it comes to the tubes has pushed me away from them. What brought on my interest was when I stumbled upon a old signal generator and especially those high end equipment are a true work of art. I i'm however tempted to try and build a tube amplifier as a gift to a friend that I think would appreciate so maybe that might lead to something in the future.However thank you very much, your information was very helpful and interesting.But I guess the tubes still must have been built up to specs as long as Muller put their brand on them? As I mentioned this comes from a high quality product so I would be very surprised if they compromised at the assembly stage but I guess tubes must have been replaced. It is only the Philips that clearly looks different from the other ones and all other tubes are marked import except for the one we talked about. Well there is the 5Y3 also that is a US made Ken-Rad tube. But assuming that they indeed used Muller BVA in all sockets form the beginning then five out of six tubes would have been replaced. I have seen a bunch of places on the internet where people are saying there is a myth that tubes have a very high failure rate and so on so it sounds like all but one tube is rather a lot. I understand that there is very little solid conclusion one could draw about this but in your experience would you say it is normal or does it indicate heavy use or bad design or so. At least for a while during it's life it seems like it attended the University so perhaps it has has a few traumatic experiences.

author: singapol
author_rank: Frequent Contributor
timestamp: November 02, 2016, 04:01:23 am
content: Quote from: Algojervia on November 01, 2016, 11:37:09 pmYou have asked a good question. To put it simply tubes that is used for audio in home environment are pretty reliable but NOS (new old stock) tubes made in 1940s onwards may not work or are not reliable ,that is there is no gauranty by sellers so buyer beware. The whole quality issue came about because of the cold war betweenUS and Russia in the 50s. Research have found that in an event of war only about 30% or less of aircraft and ships would be battle ready because of tube failures in radio,radar,sonar and other equipment.Sure you can still mobilise but you would be at a disadvantage so US airforce and navy came up with a quality control sustem and designated tubes made with the JAN label (joint airforce/navy) which is military grade.The british version is the CV label of course the Russians have their own.You have to appreciate that tubes in aircraft and ships are subjected to vibration, shock, temperature and altitude environment and failure costs human lives and military objectives/purpose..winning or losing. Normal tubes have lifespan on average 2000 hrs. and miltary grade 5000 hrs. just like everything else in life.PS It's the same with semiconducts that are military grade it's burn in to death and those that survived are sold at a premium.plus encapsulation methods ..metal can or ceramic package.Nowadays you pay more for premium tubes that are tested..that's the price of audio heaven...even then it's down to luck.( depends on equipment well designed or not.)