Valve reactivator

[Davewantsone]

We all know about picture tube reactivators.But what about valve reactivators?
With some valves getting very rare and expensive has anyone tried to reactivate one and was it successful?

[Boom]

A while back I wired my tube tester up to an ailing ECL80 and tested the emission which read low so pressed the button and after the usual sparks tested it again. The valve was well and truly dead and finished.

I suspect it can be done but you'll have to go a lot gentler than with a CRT.

[Argus25]

Both picture tube rejuvinators and valve reactivators are more of a business proposition to sell machines that do it, rather than a realistic proposition for success.

For example any CRT that requires rejuvination has a cathode emission surface at the end of its life and while partial improvements can be made to it, it is throwing good time & money after bad, analogous to welding up a rusty exhaust pipe that needs replacing.

The same is true for trying to resurrect vintage electrolytic capacitors that are unfit for reliable duty and need to be replaced.

This didn't stop a number of companies making machines claiming to rejuvinate CRT's. Though you can get some extra emission if you raise the heater voltage (temperature) for valves and CRT's at the end of their life.

There is perhaps one exception I have found. Early directly heated tubes such as UV201A's can be improved by increasing the filament temperature over a fixed number of cycles.

[space_charged]

I think CRTs may suffer more from cathode poisoning than valves do. The larger a volume is the more difficult it is to evacuate it, particularly through a narrow process tube. Also in comparison with the volume of the tube, a CRTs getters have more work to do. Maybe CRTs run at a less good vacuum than small valves do. Of course the acceleration voltage in a CRT is much higher, all adding up to more and higher energy ions flying around in a CRT than a valve. These ions are known to be involved in cathode poisoning, as is residual gas.

In short, if your valve or CRT is low emission because all of the available barium has been lost then there is nothing left to reactivate in the cathode.

If it is low emission because of cathode poisoning, then it may be possible to "flash off" the surface layer and get some emission back.

Although referred to as an "oxide cathode" the emissive species cannot be an oxide, its work function is way too high for that. During cathode activation, the barium/strontium carbonate breaks down to barium/strontium oxide. That still isn't emissive. A further slower process, involving reduction by trace elements in the nickel cathode, produce elemental barium which is the emissive species. Activation is brought about by a specific sequence of heating the cathode to higher than normal running temperatures. This is carefully controlled so as not to cause the cathode material to flake off the cathode. The conditions must also be such that no insulating layer to develops between the metal of the cathode and the oxide/barium layer.

[Welsh Anorak]

I've had quite a bit of success with reactivating colour CRTs, though I think a dead valve is a dead valve!
We have a B&K 467 which has a handy 'clean and balance' function when only one gun needs a little help. And it would usually shift cathode poisoning from a delta CRT with plenty of sparks. One thing was to run the TV immediately after treatment or else it would fail. 22" and 26" British Mullards came up well as did the equivalent Philips. Sony you could forget as they always came up worse! Ditto those nasty low focus 17" and 18" things pretending to be Mullards used in the Thorn 8000 and (gulp) Pye CT200. Mazdas did less well, and for Mullard monos we had the old bulb based reactivator. One blast only and it would work for years.
Then PIL and widescreens came and the reactivator gathered dust on the shelf.
One thing you learned when visiting those ex-rental distributors was to have a good look for a booster in use. If so you walked away!

[rogerdup]

I don't know anybody having succeeded in trying to restore a half or fully dead valve.

[linescan87]

I read here somewhere a good while ago that someone had left a low emission pl84 in a valve tester overnight and when they came back the next day it was up to 80%, so perhaps it could be possible in some circumstances.

John Joe.

[Graham G3ZVT]

PC86/PC88 UHF frame-grid triodes responded to a good tap with a 4BA nut spinner. Got you out of the house anyway.

[Graham G3ZVT]

Originally Posted by Argus25

at the end of their life.

There is perhaps one exception I have found. Early directly heated tubes such as UV201A's can be improved by increasing the filament temperature over a fixed number of cycles.

Vacuum fluorescent display tubes fall into this category, and can be rejuvenated by overrunning the filament for a few seconds. The repair seems permanent.

VFD tubes are current technology, and are often mistaken for LED by the uninitiated.

[Argus25]

Originally Posted by space_charged

I think CRTs may suffer more from cathode poisoning than valves do.

I think it is the same, it is just that the important emissive area is such a small size compared to a typical valve and the smallest degradation has a big visual effect.

Also if the CRT is for TV work, it becomes really obvious when the electron emission is low because the beam energy is spread over the entire screen. Not just a focused spot or a single line scope display.

In a sense, the ultimate test for an emissive surface is the coated cathode of a TV CRT, to be able, with a standard EHT, to illuminate an entire screen adequately.

There was an interesting test once published in a vintage Wireless World book
" Television Picture Faults" by John Cura and Leonard Stanley,1953.

An "emission image" of the TV's CRT cathode's emissive surface can be acquired with synchronized photography of the TV screen at turn off. It shows how the emissve surface fails with dark blotches on the cathode surface where the emission has failed.

Of course with time, this disease spreads across the entire cathode. I have attached the image from their book. (cool isn't it, nothing like this appeared in any other book I have seen).

Of course this is a much better test for a CRT than a global emission test on a CRT tester. And an even better test is to look at the actual picture on screen as it tests for sharp focus and the phosphor quality as well. This is one reason why CRT testers that just test gun emission are pretty well a waste of time to determine a CRT's ability to create a reasonable sharp focused bright TV image, except they will confirm if a CRT is totally defunct.

One other remarkable thing about this book, it is the only TV text I have seen where the two different problems (often confused due to the similar appearance) pulling on whites and triggering on picture affecting a crosshatch pattern are accurately distinguished and defined.

[emeritus]

Many years ago before I became familiar with valves I did bring a relative's valve radio to life by connecting a silicon diode across the ht rectifier. When I switched on, it produced firework displays inside the valves and after switching off and disconnecting the diode, sound could be heard when it was switched on again
Repeating several times brought it back to normal operation. I don't remember much about the set other than it was an ac/dc model.

[GrimJosef]

Originally Posted by Argus25

... The same is true for trying to resurrect vintage electrolytic capacitors that are unfit for reliable duty and need to be replaced ...

Wasn't there another thread about that somewhere ? Caps that need to be replaced need to be replaced. Caps that don't don't. The trick comes in being able to recognise the difference .

There is perhaps one exception I have found. Early directly heated tubes such as UV201A's can be improved by increasing the filament temperature over a fixed number of cycles.

Yes. There is a detailed reference here http://antiqueradios.com/chrs/journal/rejuvenation.html

Cheers,

GJ

[Argus25]

By GrimJosef: Caps that need to be replaced need to be replaced. Caps that don't don't. The trick comes in being able to recognise the difference .

By Argus: Yes, that is the whole point, given an electrolytic cap by its nature is a problematic part, if one is recognized to be sub standard in any way at all from its original specs, my view is replace it, not to try to help it and end up with an even less reliable part. Valves by nature are a scarce resource so its worth having a go helping to improve them, but often its futile if they are at the end of their service life.

GrimJosef: There is a detailed reference here http://antiqueradios.com/chrs/journal/rejuvenation.html

Argus: This is the reference I used when rejuvinating some UV201 tubes in my Hickok tester. The results were much better for these types than for those with coated cathodes.

Hugo.

[toshiba tony]

Yes, when the JATA and C.H. and Son reps came round they announced the "gentle" tube boosters, so we bought one. Shadowmask tubes went ok, but PIL or nearly every other type forget it. Prior to that it was the 100w light bulb, can't remember how we did it, was it deck the grid and dab full mains rectified on the cathodes. Rings a bell!

[Clydeuk]

Pretty sure I lashed up something to try and "boost" a ECC85 thinking if it was cathode poisoning it was worth a try. These valves were prone to this problem. I can't remember the details and don't think it had any effect. I remember seeing a flash inside reminiscent of a CRT booster.

The valve I tried this on would work ok if the heater volts were increased which is what made me think it might stand a chance. Anything like this would be a last resort though and probably finish the valve off.

[joebog1]

Originally Posted by toshiba tony

Yes, when the JATA and C.H. and Son reps came round they announced the "gentle" tube boosters, so we bought one. Shadowmask tubes went ok, but PIL or nearly every other type forget it. Prior to that it was the 100w light bulb, can't remember how we did it, was it deck the grid and dab full mains rectified on the cathodes. Rings a bell!

It was so long ago, I dont really remember, but what you have said is about right. I used to travel about with a tech that fixed B/W TV sets years ago.
( I was perhaps 13 or 14)
What we did was unplug the tube socket, plug our "zapper" in and switch on the TV and connect our "zapper" from topcap of 6CM5 and ground after the HT and EHT were working. . Yes it was between grid and cathode. LOTS of sparks, but afterwards the set ran again, but we did warn that the tube was on its way out.

Joe

[Station X]

Originally Posted by Argus25

The same is true for trying to resurrect vintage electrolytic capacitors that are unfit for reliable duty and need to be replaced.

Your views on reforming capacitors are well known from your contributions to other threads, there is no need to restate them in a thread about valve reactivation.

Please keep this thread on topic everyone.

[Argus25]

Originally Posted by Station X

Your views on reforming capacitors are well known from your contributions to other threads, there is no need to restate them in a thread about valve reactivation.

I thought it was a fair analogy and not off topic, as it relates to electronic components at the end of their service life and deploying various electrical conditioning techniques to try to retrieve some functional life from them.

[Boom]

Originally Posted by toshiba tony

Yes, when the JATA and C.H. and Son reps came round they announced the "gentle" tube boosters, so we bought one. Shadowmask tubes went ok, but PIL or nearly every other type forget it. Prior to that it was the 100w light bulb, can't remember how we did it, was it deck the grid and dab full mains rectified on the cathodes. Rings a bell!

One unmentionable way we did it but only with valve sets and as they were rental no one gave a stuff anyway and it saved a trip back to the workshop to collect the booster was simply to hold one of the Avo leads on the CRT grid and briefly flash the other lead to the top cap of the PLXX