NOS Valves. Getters not fired from new.

[Heatercathodeshort]

I have been tidying up a Bush TV62. The EY86 EHT rectifier was a bit low emission causing a slight increase in the size of the picture when operated at high brightness levels.

A hunt through my valves produced a NOS Mullard 5 pack of final production EY86/87 valves. I pulled one out of the sleeve and confidently fitted it to the LOPT in the TV62.

To my surprise it was gassed producing a bright pink/purple glow as the line stage warmed up. Further investigation showed that the ring getter at the top of the valve had never been fired and neither had it in the remaining four valves in the sleeve, all giving the same light show as the first one. It is now 100% with a NOS Pinnacle valve.

They obviously slipped through and would have passed test wise but after all these years molecules of gas must have leaked from the electrode assembly and there was no getter to mop it up. I have seen the odd valve that has never been fired but not a whole pack! John.

[davidh1041]

I have also found some NOS EY86 where the getter had not been fired, how strange. Unlike Mullard to have quality control issues.

[linescan87]

If you were able to fire the getter now do you think it could be enough to "mop up" the gas molecules in the valves or would they be gone too far?

[Heatercathodeshort]

You might be able to salvage them but not worth all the trouble. The cathodes may have been contaminated. Fortunately EY86 valves are still around in quantity. Date code was 1971 J.

[Radio Wrangler]

Somehow I don't think they have the value of a period stamp with the perforations missing, John.

David

[1955APREN]

Now where is my BVA claim form
Derrick

[eddie_ce]

I hope this is not a stupid question.

Is it possible to see if the getter has been fired, and if so how? I also have some NOS Mullard EY86s, so would be interested.

Thank you.

[AC/HL]

They should have a silvery coating inside: http://www.r-type.org/exhib/aaa0153.htm

[eddie_ce]

AC/HL - thank you
I have compared 2 Mullard EY86s with 2 Mazda examples, all NOS

The Mazdas have a silvery/black coating inside the glass envelope near the base of the valve.

The Mullards have no such coating visible. Is there possibly a reason for this or is it more likely to be an omission during production?

[Leon Crampin]

You can fire the getter by using a microwave oven. It's risky, but select full power and keep your hand on the oven off button. You need to watch carefully in the 2 seconds or so that it takes for the magnetron cathode to heat, then turn off as soon as there's a flash inside the valve.

I've restored a few valves this way - and broken some. The oven survives.

Leon.

[high_vacuum_house]

I have seen a few late manufactured valves with poor quality control from Mullard. I have an octal line output valve that had a stack of 5-6 ring getters all together on the anode cap wire. Non had been fired as there was a gap in all of the rings where it had missed the spot welder.

I noticed some eht rectifiers don’t have any getters at all or have a non evaporative getter fitted. Presumably this is to prevent the metal film causing a flashover.

Christopher Capener

[Nuvistor]

According to the link in post 8 early EY86’s didn’t have a getter, is it possible they were old stock when put into new boxes.
Without a getter, contamination and slight leaks over the years could have finished the valves off.
http://www.r-type.org/exhib/aai0214.htm

They possibly wouldn’t have been making EY86’s in the early 1970’s when I think they introduced those boxes? Is there a date code on the valves?
Just thoughts and ramblings.

[high_vacuum_house]

In the pictures of the EY86 here: http://www.r-type.org/exhib/aai0214.htm it states that there is no getter though there is a non-evapotatable getter visible fitted between the base and the electrodes in the form of a small sheet of nickel with a dimple in it. This would be filled with something like zirconium which is heated by an RF heater but does not volatilise onto the glass. This is a more expensive material than barium but it doesn’t cause a metal film deposit on the glass.

Christopher Capener

[stevehertz]

Looks like they've just gone gassy then.

[Jac]

I have a Valvo, Philips and Lorentz EY86/87 without any visible getter action, but they are working fine.

Jac

[Radio Wrangler]

Originally Posted by high_vacuum_house

I noticed some eht rectifiers don’t have any getters at all or have a non evaporative getter fitted. Presumably this is to prevent the metal film causing a flashover.

Quite common in high voltage transmitting valves. Evaporative getter material van get in the wrong place and form conductive film on parts that should be insulating.

So the routine is to not use getters, but then to have a better evacuation scheme in manufacture. With a chemical getter, they don't have to be pulled down to such a good vacuum. Without the getter, the backing pump needs to be front-ended by something much more serious like a diffusion pump. Needless to say plenty of time is needed for outgassing and more care over heating to speed up outgassing.

TV EHT rectifiers run even higher voltages and small leakage currents would be more significant than in high power bottles, so I wouldn't be surprised to see getterless or non-evaporative gettered constructions.

But the photos earlier seem to show a normal ring getter and space for it to work. Maybe they really haven't been fired?

David

[Heatercathodeshort]

They are coded 1971 from my old shop stock. I suppose they were never required as the DY series had become the standard EHT rectifier from around 1964. I don't think I ever replaced a EY86 focus rectifier in a Bush CTV25.

I have plenty of old style used EY86 that are all OK! I think I'll stick to pulls! John.

[peter_scott]

Originally Posted by high_vacuum_house

This would be filled with something like zirconium which is heated by an RF heater but does not volatilise onto the glass.
Christopher Capener

Would red heat be sufficient? The little Chinese induction heaters are cheap.

Peter

[Heatercathodeshort]

That poor EY86 Peter. Pure torture! John.

[Radio Wrangler]

I'm not sure of the value of firing getters now. They were intended to be fired while the valve was on the vacuum pump because some gas was given up when the getter was fired. Nitrogen or hydrogen, I think. It was a materials physics lecture a long time ago.

David