There doesn't seem to be much on this subject; I have recently purchased a fairly big lot of noval valves in boxes which have at some stage in storage become wet. The circular cutout in the cardboard which retains the pins has caused the pins to corrode right against the glass envelope. The green corrosion can be removed with a brush but 20% of the valves are ruined-the getter has turned completely white. The remaining 80% look ok with the getter still looking pristine. Can I have any confidence at all that they actually are ok and will not fail early in use? Has anyone else encountered this problem?
The non-abrasive method for cleaning corroded steel pins is to soak them in lemon juice for a few hours. Lemon juice contains citric and ascorbic acids, neither of which is particularly strong, to quickly attack the metal. Ascorbic acid is a reducing agent and will convert the Fe+3 species into Fe+2. The citrate ion is a good complexing agent. Between ascorbate and citrate, corrosion products enter solution.
After the soak, rinse with water and wipe dry, with a paper towel. Ensure moisture is eliminated by a final flush with anhydrous isopropanol.
After the soak, rinse with water and wipe dry, with a paper towel. Ensure moisture is eliminated by a final flush with anhydrous isopropanol.
Thank you for your replies. Actually, the corrosion is nothing like normal iron rust, it is globules of a bright green colour (a nickel ion, if I remember correctly my high school chemistry? ) A non abrasive brush removes most of it. My main concern is the likely health of the valves once they are put to use given that the getter has been already totally destroyed in a fifth of them.
I used to use P1200 grit wet and dry sandpaper in a small strip wrapped around the pin and gently rotated, it's the best method I tried and worked perfectly every time. Coke (of the cola kind) or even vinegar can also work but not so well and you have to clean the pins with rubbing alcohol afterwards.
I never used a wet solution to clean larger power valve pins in case it seeped inside the cap where it can't be cleaned out. You can of course leave small capless signal valves or EL84's etc with their pins standing in a dish full of a solution for a few hours.
I found the very fine grit sandpaper approach worked best with all of them, just remember to clean off the dust afterwards though.
I found the very fine grit sandpaper approach worked best with all of them, just remember to clean off the dust afterwards though.
Plunging the pins into a Schotchbrite pad helps to clean them up if they are just oxidized (mostly, they are). I never tried the lemon juice dodge, but then I don't have any really corroded tubes except for some NOS 1625s whose boxes obviously got really wet. Scotchbrite and a fine wire brush worked in that case (different pin material).
I got over 100,000 tubes that were loosely boxed and left in the Florida humidity for about 25 years. Many of the 7 and 9 pin tubes had the green growth. Some were so bad that the pins would break off when touched. Some were in better shape.
I used WD40 and a toothbrush to clean the green stuff off and most of the tubes were OK. I had the pins of some of them break off in a tube socket when testing, so I went through all the keepers and gently wiggled each pin and tossed the ones that snapped.
After cleaning and testing I wound up with about 500 6AQ5's and the ones that I have used so far have held up OK under hard service.
I hooked up some of the really green ones with clip leads and many of them worked. I used these with clip leads to find their "melting point."
It seems odd that all the tubes were in the same situation but some types were affected far worse than others. All were "pulled from military spares" and therefore used, so maybe prior use affected the outcome. The 6J6 types including 6J6WA and the military types with 4 digit numbers were by far the worse with over half of them being discarded. There were several thousand 6AK5's and very few were corroded.
I used WD40 and a toothbrush to clean the green stuff off and most of the tubes were OK. I had the pins of some of them break off in a tube socket when testing, so I went through all the keepers and gently wiggled each pin and tossed the ones that snapped.
After cleaning and testing I wound up with about 500 6AQ5's and the ones that I have used so far have held up OK under hard service.
I hooked up some of the really green ones with clip leads and many of them worked. I used these with clip leads to find their "melting point."
It seems odd that all the tubes were in the same situation but some types were affected far worse than others. All were "pulled from military spares" and therefore used, so maybe prior use affected the outcome. The 6J6 types including 6J6WA and the military types with 4 digit numbers were by far the worse with over half of them being discarded. There were several thousand 6AK5's and very few were corroded.
All were military surplus from the WWII through the mid 1950's, so there were plenty of useless thyratrons, 10KV rectifiers, klystrons, magnetrons and T/R tubes, but no 300B's. There were however several 211's and 845's. They made their way into my amp.
I never tried it. I used WD40 since I had it, and I still live in the land of perpetual high humidity where tube pins turn green, and tin plated connector and switch contacts turn white.
It took me over 5 years but I have gone through and sorted them all. There were about 10,000 useful tubes, of which I still have about 4000. I will be moving all of my belongings about 1100 miles next year, so I have been reducing my collection over the last few years. Yes, I was actually giving away free sweep tubes to forum members at the Dayton hamfest this year.
Tubelab, none of the pins that I am talking about seem quite as bad as you are describing but yet the actual vacuum has failed in 20%. Did you notice such a high incidence of getters turned white? Is it possible that I am attributing an invalid causal relationship between the corrosion and the getter condition?
The tubes I got had been pulled from military spares, sorted and placed loosely in boxes on shelving. They sat pretty much untouched for 25 years. The rats and roaches ate away much of the boxes, In some cases there were just piles of bare tubes on rusty shelving. The tubes were only a small part of a large colletion of military surplus.
Aparently the tennant who stored all of this had passed away and the warehouse was unopened for at least 5 years. The land owner had sold the property and it was scheduled for demolition. The contents, including the tubes were being scooped up with a front end loader and dumped into trash dumpsters when a friend of mine found out about and bought the lot. He was given 2 weeks to remove it all. A crew of workers just dumped the stuff in boxes and delivered it to my friends parking lot, where it all sat. My friend called me and said if I helped him sort and move it into his warehouse, I could have all the tubes.
So yes, over half the tubes had white getters, but most of them were physically damaged. I found at least a dozen RCA 211's that were smashed
There were several bulk pack boxes of 6J6WA's and about half had green pins, and many had white getters. The boxes were in various states of decomposition, but that didn't seem to matter, there were bad tubes in the good boxes. Storage could have contributed to this.
On a different note, About 20 years ago I went with my friend to pick up a lot of surplus that he had bought from the NASA cape Canaveral space center. There was an unopened box of 100 Sylvania 6V6GT's that had been sealed in 1970 and never opened. They were from an air conditioned storage facility on the NASA complex. I took it home and opened it to find that about 30% of the tubes had white getters. I tossed all the white tops and tested every tube throwing out several more that showed gas. The box has been on a shelf in my air conditioned house ever since, yet tubes keep turning white with time. There are only about 25 good ones left. Some of the tubes are OK and have seen use in SSE's and guitar amps, but I can't trust them.
Clearly Sylvania had some problems in manufacturing in the later days of vacuum tube manufacture. I have found other evidence of this....35LR6's NIB that could never have worked, and some small 9 pin tubes with an extra heater loose inside the envelope. I have TWO of those, so how many were made.
Aparently the tennant who stored all of this had passed away and the warehouse was unopened for at least 5 years. The land owner had sold the property and it was scheduled for demolition. The contents, including the tubes were being scooped up with a front end loader and dumped into trash dumpsters when a friend of mine found out about and bought the lot. He was given 2 weeks to remove it all. A crew of workers just dumped the stuff in boxes and delivered it to my friends parking lot, where it all sat. My friend called me and said if I helped him sort and move it into his warehouse, I could have all the tubes.
So yes, over half the tubes had white getters, but most of them were physically damaged. I found at least a dozen RCA 211's that were smashed
There were several bulk pack boxes of 6J6WA's and about half had green pins, and many had white getters. The boxes were in various states of decomposition, but that didn't seem to matter, there were bad tubes in the good boxes. Storage could have contributed to this.
On a different note, About 20 years ago I went with my friend to pick up a lot of surplus that he had bought from the NASA cape Canaveral space center. There was an unopened box of 100 Sylvania 6V6GT's that had been sealed in 1970 and never opened. They were from an air conditioned storage facility on the NASA complex. I took it home and opened it to find that about 30% of the tubes had white getters. I tossed all the white tops and tested every tube throwing out several more that showed gas. The box has been on a shelf in my air conditioned house ever since, yet tubes keep turning white with time. There are only about 25 good ones left. Some of the tubes are OK and have seen use in SSE's and guitar amps, but I can't trust them.
Clearly Sylvania had some problems in manufacturing in the later days of vacuum tube manufacture. I have found other evidence of this....35LR6's NIB that could never have worked, and some small 9 pin tubes with an extra heater loose inside the envelope. I have TWO of those, so how many were made.
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