Cooking Your Eimac 3-500Z Filament To Degass The Tube 

I have been working on for hours. I think I have something worth seeing so I will do my best to post the results very soon. Stay safe.

I totally agree. The marriage of glass and metal and vacuum and how, in one way they are so fragile, and in another way they are so powerful, is down right magic.

Hi Frank - good to hear you are doing well. I brought out a PS today and started trying to get the plate to turn red by placing the PS directly across the tube with a Variac on the HV transformer. I can't get the Ip higher than about 60mA and the tube ionizes right at 2KV and blows fuses. I got tired of risking my nice amplifier for this experiment. Then I put a little positive grid voltage on the 4-400A to (hopefully) increase Ip. No luck so far. If I could get the Ip to about 400mA at 1Kv or even 1.5Kv, I would be dissipating 400 watts in the plate and some have convinced me if I can make the plate turn orange, as it is supposed to, it will "getter" the tube. It sure isn't very gassy or the filament would not be so perfect. There are no DC shorts as I checked for the obvious and I even used a capacitance meter to see if it would read from grid to plate, screen to plate, etc the same capacitance as a good tube. While I am pretty convinced all this is hoop-la about bringing one of these tubes back to life, just at you are, some people claim they have done it and they are people that comment on my videos and I believe them. This may work for some tubes but not all. Doctors would call it anecdotal, my experience may not be yours and yours may not be mine. Somehow, I am still convinced that this is possible. I just have to be Very careful around this huge PS I have on the bench. I will probably make a video of it either way. Stay safe.

Time to get a glass cutter

Ive seen those "Getter's" on the 3-500Z tubes, the little square plate attached to the pin inside underneath the circular plate? There are two of them.🤓👍

@@ericdee6802 No, the getter material is a coat of zirconium on the anode.

Hi Manuel, it is so good to hear from you. I have thought of you so many times being in Italy. I hope all has been well with you and your family. All is well here, thank God. I have set up a tube-cooking arrangement in my shop using a big HV PS with the 872A rectifiers in it. I can not get the voltage over 2KV without it going critical and blowing the fuse. I set this up as I did not want to risk damaging my real amplifier. I can not get plate current over 60mA so the plate does not heat up. I put a 9 volt battery with the + side on the grid to help increase cathode current but no luck so far. This tube may not be salvageable but from all the comments left, I can see that it has worked in some cases. As I mentioned to another comment, these types of things are anecdotal, that is, what works for me may not work for you and what works for you may not work me. That is what a doctor would label it. Anyway, I will work on it a little bit more tonight and if I can document it, I will post another video. Stay safe...

@@ElPasoTubeAmps nice to see that you warring for me, yes i am fine as well as my family. i am still actively working since my occupation is in an essential facility but we have to follow very rigid protocols to keep us safe. the current situation here is getting better, but still for some time it was like a war bulletin. stay at home and safe!! well if your tube can not get even hot without an internal ark i agree that it is busted, as you say it probably works only if caught in time. looking forward for the follow up! oh btw... the power supply is still a work in progress, as promised i will send you a board :)

That would be fun and dangerous... couldn't be much more dangerous than some of the contraptions I see build on RU-vid for heaters. 🙂

The purpose Eimac specifies is to cool the filament seals and the plate seals so, if the chassis is designed to be pressurized under the socket, the air flow will from the bottom thru the holes in the socket around the filament seals and then upward over the bulb and finally out the top across the plate stem/glass seals. Mostly the builders just put a muffin fan blowing across the tube from the side. A lot cheaper so the chimney cooling system would likely be used for commercial and military equipment unless us crazy hams can get it and use it. ..

afaik, these RF tubes don't have a getter. they glow the plates white-hot to burn off any impurities. well actually more like red-hot but you get the point, HOT.

@@EdgarsLS its actually the other way round you get the plate hot to burn in the impurities lol they react with the plate and form oxides and nitrates etc so the plate absorbs the gases (the plate is the getter)

Absolutely... just because they are truly NOS, it does not mean they will work and "cooking" them is worthless. I am almost of the opinion that the vintage ones that are truly used are likely to be better off than the ones that are 50+ years old and have never been used. One thing for sure, in my opinion is and this example, once they have shown failure, they are bad forever and no amount of "cooking" is going to change anything.

@@ElPasoTubeAmps I agree.....the ones I had were definitely brand new as I had to get them out of the cans myself with a can opener, yet the fail rate salvaging out of recently existing working gear is much less......anyway , Cheers David good to see those Video's coming out again..........its great for us old Tube Jockeys to have something to watch .

Thank you for the link. This site was recommended to me below in a comment and I have read thru it thoroughly and tried their procedures. Right to the point - it appears my tube is beyond help. It is interesting that strapping the grid and screen to the plate and turning it into a diode will allow me, with this particular tube, to increase the voltage to a point that I can get the plate cherry red with lots of blue and the voltage across the tube is only about 60 volts with 6A of current. Yes, six amperes of plate current - that was not a typo. At that point, the plate is dissipating 360 watts and is red and better than 400 degrees F. You might think, how can the cathode do this? Well, it can but I am convinced it is because the tube is gassy. When I put in a good tube into this "test" socket, no matter how high I raise the plate to cathode voltage, (max 100 VDC) the plate current never goes over about 800 mA and the good tube shows no plate color and no blue glow and it works perfectly afterwards in my amplifier. Back to my original belief in this degassing process is, it is worthless. It is probably a good idea to let the filament run for a few minutes and after that put the HV to the tube. It will either work or not and you will save a lot of time that will likely deliver nothing. In my opinion, going thru this routine before putting a tube like the 3-500Z into operation and then having it work, would be just as successful if you did nothing other than the obvious of checking the tube for clean pins and no bits and pieces of material rattling around inside the tube, etc. Just my experience which is anecdotal. 73 and stay safe.

I don't want to discourage you from trying to make your 4-400A work again. It is interesting how they can look new and the filament light properly and be bad under HV. Some depending on the level of high voltage. There are rituals where some individuals believe if they allow their tubes, especially the 3-500Z filament(s) to "cook" for a day or two before applying HV, it will make them work better and last longer by "degassing" them. That is anecdotal - it may appear to work for some but not for others. No one can say for sure that it doesn't help but in some cases it is not going to help. Eimac says the tubes must be heated to temperatures just below destruction of the tube in a laboratory controlled environment to make the "getter" function in the anode do its job. If it is already beyond help, it won't hurt it any further - just be careful not to get electrocuted or burn yourself as these tubes get really hot... 73 Stay Safe.

Thank you

Once it ionizes, it must be pretty much a complete short on the PS as it instantly blows a 20A house fuse. I have house fuses on both sides of the line in a screw in fuse block in the power supply. I guess that was really more of a golly-gosh-darn moment... you have no idea how I control myself while in front of the camera :-)

@@ElPasoTubeAmps I was joking about the potty mouth,.. I can only imagine the frustration!!

The good gentleman on Ebay said he would give me my money back for it so I may have to send it back to him.

ElPaso TubeAmps That’s great!

Hi Don, I hope your 3-500Z's are good also. Getting pretty hard to find the Eimac 3-500Z's anymore. I had had a pair of Chinese 3-500Z's and they did work OK but my vintage Eimac 3-400Z's outperform them so I ended up selling the 3-500Z's as I have plenty of the 3-400Z's. More to the point here - I personally have no faith that these "degassing" procedure(s) is worth a hoot. But that is just my experience. I am not discouraging the procedures as maybe they will help and if you do as I do and just plug them in and let them warm up for 5 minutes and put the HV to it and they don't work... you might regret skipping the degassing procedures. Who knows. The tube I used in this video will not work no matter how many degassing procedures I have used on it probably because it is already just too late. So many people believe in these procedures that it is hard to completely disregard them. The only thing that I can personally find in legitimate Eimac literature is to leave the filament(s) on for a couple (few) hours before applying HV. Eimac literature says if this does not "degass" the tube, there is nothing you can do about it. All this stuff about the plate being the "getter" is not something that I can find that Eimac says and seems to me to be just ham radio lore passed down thru the generations. I may be wrong. If I am wrong, I hope someone will enlighten us by directing us to where Eimac (or any other legitimate transmitting tube manufacturer) gives this information. From other ham radio lore, it seems that older tubes that have been used are more likely to work decades later than the truly, completely unused, brand new, NOS tubes. For some odd reason, I tend to believe that one. As you see in my video, I have a nice stash of tubes, including three 4CX1000A's that were given to me brand new around 1983. I have opened everyone of them long ago and used them and did not leave any of them in their sealed container. They all work perfectly nowadays. The same for the 4-125, 4-250 and 4-400 and even the 3-1000Z's I have. I can not leave well-enough alone and swap these tubes around ever so often just for something to do. Maybe that is why they all still work. Those are my personal findings at this time. Practically all of my tubes were bought used and they still work. I do have some pretty weak 833A's and surely others that are not 100% - but they still work and are all around 50-60 years old. I am 70 years old and I still work - and I don't need degassing... :-) I do power up pretty slow in the morning but I can sure stay up late at night. Just ask my wife. In any case, be safe around that 2500 volts in your SB220/221 and be just as safe by not getting the virus going around. 73 WA4QGA

@@ElPasoTubeAmps If you were too gassy I'm sure your wife would have already found a good degassing method. :)

@@jamescrabb8766 ha..ha..ha.. 😀😂 De VU2RZA 👍❤️

It is funny how these ideas get started but once they propagate thru the ham radio community they are impossible to debunk completely. It seems any attempt to prove they are all but worthless may just get interpreted as a conspiracy. Lies and misinformation propagates several times faster than the truth. Just look at TV and the Internet and social media.

In this test setup, the grid is strapped to the plate so even at 90 volts or so, which has to be carefully controlled with a Variac, I can turn the plate as orange hot as I want and, of course, keep a fan on it to cool it, and then let the plate run red hot for several minutes to "degass" and it simply doesn't work on a tube that is just a little bit too gassy. I say, a little bit too gassy, as they filament lights normal so it is not full of air as it would immediately fill the inside of the tube with white smoke as I have seen really bad tubes do. My conclusion, not from just this example, is the whole idea of heating the anode to hot temperatures to "getter" (absorb) the gasses inside the tube is wish-full thinking. It doesn't work and in my opinion is a waste of time. I know fellows go thru this routine on their 3-500Z amplifiers that have been off for a few years and report great success. I plug in tubes, like the 4-400A and many others that are 50+ years old and turn them on and apply 3500 volts seconds later and have never had a problem. The tube is either good or bad and if bad, there is nothing we can do to save it, unfortunately.

The plate itself is the getter, but must reach a certain temperature to work.

This has been extremely valuable. Too much to put in writing but I will be making a video of the results from this procedure soon. Thank you. Stay safe...

Good luck!

@@stirlingschmidt6325 I have read thru that article very carefully and I find it very valuable in both the way they test the tube by turning it into a diode and the value of cathode current for a set voltage he shows in his charts. I believe the 4-400A was about 350mA for 44VDC. However, I have found that on a good tube, the plate voltage can be increased to as much as 100 volts and the current will rise to around 1A and stabilize and rise no further. I know that is over-current for the cathode but please watch my next video that is processing as I write and see how a good tube performs (actually three good tubes) compared to how this tube behaves. I have done all the degassing that these procedures document and maybe they help some tubes but this tube certainly seems bad and just isn't going to be rejuvenated. I thank all of you guys so much for your suggestions and comments.