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Non destructive Tube Reactivation, Updated!

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Re: Non destructive Tube Reactivation, Updated!

Post by Alastair E » Mon Feb 18, 2013 9:50 pm

Mark--

I think providing that you take your time, let the CRT warm up well--say at least 10 mins before you try anything, (I think this pre-heating stage may be important with tired old cathodes) --limit the current by resistor first to 5mA and keep the voltage at around 150, there'll be no arcing to cause an issue, I very much doubt it will kill it.

How bad is the CRT in the set? If the picture is reasonable and you haven't a source of, or a spare CRT, maybe enjoy the set for a while till it gets too bad....

 
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Re: Non destructive Tube Reactivation, Updated!

Post by Michael Watterson » Mon Feb 18, 2013 10:08 pm

Try running the really knackered ones (that have not improved enough to be used) now with NO HT and +25% heater for about 4 hours and repeat the HT procedure? What is there to lose?

 
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Re: Non destructive Tube Reactivation, Updated!

Post by mark pirate » Tue Feb 19, 2013 1:09 am

How bad is the CRT in the set? If the picture is reasonable and you haven't a source of, or a spare CRT, maybe enjoy the set for a while till it gets too bad....


The picture is dim but watchable, but does go negative with the contrast or brightness turned up, I am waiting for delivery of an EHT capacitor to replace the visconal, from experience this could give me an extra 1Kv of EHT, I also have a NOS EY51 to try as well, but if it is still dim I will give it a go.
Cheers
Mark

 
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Re: Non destructive Tube Reactivation, Updated!

Post by Alastair E » Tue Feb 19, 2013 3:07 pm

Michael Watterson wrote:Try running the really knackered ones (that have not improved enough to be used) now with NO HT and +25% heater for about 4 hours and repeat the HT procedure? What is there to lose?


Oh--4 Hours! wow, I think maybe a little less time would be better! Doubt I would try much more than 15 mins at first!

Those heaters are after all many thousands of hours old and cant be that strong anymore!

 
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Re: Non destructive Tube Reactivation, Updated!

Post by Michael Watterson » Tue Feb 19, 2013 4:09 pm

I did say "really knackered" :D

 
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Re: Non destructive Tube Reactivation, Updated!

Post by sideband » Tue Feb 19, 2013 7:22 pm

Alastair E wrote:Those heaters are after all many thousands of hours old and cant be that strong anymore!


Well it's your tube and entirely up to you of course. The heaters are a lot tougher than you may think. We had a Decca DM2-C for many years and the tube was knackered to say the least. my brother fitted it with a boost transformer originally on 25% and it made the tube look new. A few years later it had shown signs of going flat again so this time having gained enough knowledge myself, upped the boost to 50%. The glow behind the TV was quite impressive with the main lights out...a definite pattern of the ventilation slots could be seen. It was still giving a good picture several years later when we finally bought a new set.


Rich

 
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Re: Non destructive Tube Reactivation, Updated!

Post by Alastair E » Wed Feb 20, 2013 10:25 am

I guess so.....

The heaters I'm assuming are tungsten so can put up with 2500 degrees...

Worth keeping in mind the boiling-point of the barium metal that does the emission is around 2100--a bright yellow heat...
Boiling implies to me--evaporation (and loss) of this material.--Maybe I'm wrong--its all a bit too nuclear physics for my addled brain!
--If evaporation does occur--where does the stuff collect?--Probably condenses on the cooler grid close by, what effect that has I'm not sure-'grid emission' maybe....?

I think what we are trying to do is to drive fresh material from deeper in the coating to the surface, keep it there and also remove the interface layer that I Think causes resistive and presents a capacitive 'layer' between the surface and the metal of the cathode cap.

Most 'boosters' do increase the heater-volts during reactivation by 25% ?, so guessing it cant be too destructive if done carefully...
--I wish I had a few really bad unboosted CRT's to mess around with. All I have is an untested A56-120X, a good A49-91W, and that Sony--which now is good....

Guess I like to err on the cautious side.... :thumbr:

 
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Re: Non destructive Tube Reactivation, Updated!

Post by peter scott » Wed Feb 20, 2013 1:13 pm

ppppenguin wrote:I wonder if this method could improve the 6/6 in my Marconi 702. It seems like a low risk method.


Alastair's procedure sounds good. I too amvery interested in any results you get Jeffery.

Peter "£"

 
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Re: Non destructive Tube Reactivation, Updated!

Post by Alastair E » Wed Feb 20, 2013 9:57 pm

For want of something better to do and to find whether it was any good, I tried the procedure on the Mazda A56-120X CRT I rescued in the Thorn 3000 from the tip.

Each cathode started out giving me 4mA ish. (145V, 18K, 6.5V heater)
This quickly rose to 7.5mA within half a minute

I left the CRT cool, re-heated and re-tried.

I got readings of 7.5mA on all cathodes immediately.

So--I have what looks to be now a good A56-120X CRT and No Philips G6 to put it in, Doh! :~

 
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Re: Non destructive Tube Reactivation, Updated!

Post by Merseyswimmer » Thu Feb 21, 2013 6:54 pm

Murphyv310 wrote:One collector I know was running an MW43-69 with 50% boost for literally years. The set got trundled 60 miles to me for repair at one point and still the tube ran merrily away for years after :eek:


The old Bush TV54 my parents bought new in 1953 was still going strong to the late 1960s despite a booster transformer being fitted around 1963. I still have the old set in my bedroom but it hasn't seen power since 1969. This despite glowing like a light bulb the heater was intact when the set was last used.

Pete

 
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Re: Non destructive Tube Reactivation, Updated!

Post by slidertogrid » Sat Feb 23, 2013 11:02 pm

I have been following this with interest as I have an Ultra BBC only set with a Mazda CRMXXX in it, it is in the spare room awaiting it's turn. My main worry was that the crt would be flat, I should now be able to find out if there is hope!
Reading back issues of Television magazine it seems the Mazda Crm series were going flat not long out of guarantee, there was even mention of this being designed in by Mazda!
I had a Bulb bopper back in the days of delta gun tubes and found that it worked well on Mullard 90 degree colour and most mono tubes.
I found the best way to extend the life of PIL and 110 tubes was to overrun the heaters slightly, A lot of sets had a resistor in series with the heaters that could be dropped slightly, KT3 s K30s etc we would start with shorting half of a heater choke on the crt base...It was somtimes years before you were down to one and a half coils shorted! wurhurr
The ones I didnt have a lot of luck with were the Toshiba tubes as fitted to some GEC sets and Decca/Telefunken 100 chassis they seemed to go intermittent h/c short or flat very quickly if messed with!
Just my 4d th!
Interesting thread!
"£"
Rich.

 
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Re: Non destructive Tube Reactivation, Updated!

Post by Terrykc » Sun Feb 24, 2013 1:42 am

slidertogrid wrote:... Reading back issues of Television magazine it seems the Mazda Crm series were going flat not long out of guarantee, there was even mention of this being designed in by Mazda!

That was in the mid 60s. Our Mullard rep referred to it their built snuffer!

The next time we saw him he wasn't so happy. A rental company (Kellys?) in the Southend area had a large number of 23" Bush sets out on rental and most of the tubes were flat at 18 months old.

Interestingly, Bush had always used Mullard valves and tubes but, when Rank took over Murphy, a long time Mazda user, the first sets where split 19" Mullard and 23" Mazda ...

Anyway, the company protested vigorously to Mazda about the duff tubes as they couldn't afford to bear the loss. Mazda coughed up but on condition that they also signed up to a bulk supply deal to get all of the valves from Mazda in the future - so Mullard lost a sizeable chunk of business.

Shortly after this there were great fanfares in the trade press as Mazda announced that they were extending the tube guarantee from one year to two!

 
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Re: Non destructive Tube Reactivation, Updated!

Post by Doz » Fri Jan 24, 2014 5:22 pm

Tried this out this morning on a sad Sony TV-110. Unwatchable dim and poorly focussed before. After 3 hours, bright and sharp :aad

The contrast control is no nowhere near the top !

My set up involved a variac, isolation TX and my capacitor reformer to limit the current (It has switchable current limiting resistors) .. looks like it doubles up as a tube reformer too!

 
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Re: Non destructive Tube Reactivation, Updated!

Post by Michael Watterson » Thu Feb 20, 2014 11:15 pm

Sadly true.
Also you know that the higher a heater transformer is set the faster the tube wears done. I sure you know. New folk might not know that BEST life is just enough to make it usable, don't be greedy :) . Driving to make it as good as possible can finish it off in days.

 
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Re: Non destructive Tube Reactivation, Updated!

Post by Alastair E » Thu Apr 17, 2014 1:36 pm

I can add an AW36-21 to the list of successes....

The dodgy heater CRT in my TV62 benefited from the treatment.

Because of the heater issue, I have added a transformer (12V) and a series resistor of 22 ohms. This gives me a heater-voltage of 5.6v. Connected in the chain, I was only getting 4.6V.

The restoration was done at 6.3V (too much for this CRT because of the heater issues) and a 33K in the 140V supply.
Initially, the voltage developed across this 33k limiter resistor was only 70V. This fell slowly to 30, and then started to climb over approx 5 minutes to 117v, where it seemed to stall.

I removed the supply to the cathode/grid and just let it sit for 10 minutes.

Checked again and the voltage had gone up to 127V. Left it again for 10 minutes without cath/grid volts and then re-checked. Same at 127V
Not wanting to push my luck,--I disconnected everything, and tried the set.

Much better picture, more contrast and brightness with no sign of silvering effects or negativity....
In the set, its running at 5.6V heaters via the transformer and resistor, giving perhaps a slightly dull cathode but comparable with the others still in the chain....

 
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Re: Non destructive Tube Reactivation, Updated!

Post by mark pirate » Mon Apr 28, 2014 9:07 pm

I have had good (and lasting) results using the 'clean & balance' setting on my B&K, although I am a bit worried about risking it on my CRM92 & 121 CRT's as these are both in restored sets, although pretty dim they do still work!

 
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Re: Non destructive Tube Reactivation, Updated!

Post by Alastair E » Sun May 04, 2014 5:27 pm

I'm wondering whether the CRT condition before the 'non-destructive' method has a major bearing on the outcome....

The CRT's that I personally tried, did show pictures, although far from perfect, just poor, a bit dim and out-of-focus--ie Just Flat.
In the case of the TV62, it also had silvering that disappeared after some time when used. This showed a marked improvement

Its a shame it didn't improve the other posters CRT's as was hoped....

 
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Re: Non destructive Tube Reactivation, Updated!

Post by Katie Bush » Mon May 05, 2014 11:27 pm

Hi all,

Just for my tu'pence worth, I wonder if a "clean and blance" on the B&K, followed by a slow bake, might be worth a shot?

My thinking is, clean off the dead surface layer, then a slow bake to level off any irregularities in the surface.. My thoughts were wandering back to the notion of bringing "new" material up from within the cathode, as was suggested quite some posts back.. If so, would this new material help to smooth the cathode surface? Or am I of on a wrong tangent here? Even if it did smooth the surface, would it actually have any benefits for the cathode?

Marion

 
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Re: Non destructive Tube Reactivation, Updated!

Post by mark pirate » Tue May 06, 2014 2:17 pm

Just for my tu'pence worth, I wonder if a "clean and blance" on the B&K, followed by a slow bake, might be worth a shot?

I always set up the B&K and let it cook for around half an hour before checking emission again, usually it does come up ok. but if not,the next step is to cook it a while longer with the heater voltage raised before doing a clean and balance. Hitting the rejuvenate button is a last resort!

 
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Re: Non destructive Tube Reactivation, Updated!

Post by crackle » Wed Oct 22, 2014 3:48 pm

I tried this today with my KB PVP20 tube.
I used my valve tester set to 160v for the HT supply and a bench DC supply for the heater supply (set to 7v)
I had a 22k resistor in series with the HT supply.

After giving a good long period for the heater to warm up the HT was applied and the current was 3.8ma, before I could setup my camera it had risen to 4.8ma. It slowly and steadily rose and after about 20 minutes it had stabilised at 5.5ma. I switched off the HT and left the heaters on for another 10 min.
The tube on this TV takes a long time to warm up and the picture stabilise, If I had given the tube another minute to warm up on the second photo then the image would have been the same size as the before photo.
The results are below.

The shadows across the screen in second picture are I believe interference patterns caused by the camera when the photo was taken, there was no such shadow on the screen.

All controls were left unaltered for these tests. However the brightness and contrast controls could be turned up more and still maintain a clear picture.
Mike
Attachments
tube boosting.jpg

 
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Re: Non destructive Tube Reactivation, Updated!

Post by sideband » Wed Oct 22, 2014 6:46 pm

Crackle wrote:The tube on this TV takes a long time to warm up and the picture stabilise, If I had given the tube another minute to warm up on the second photo then the image would have been the same size as the before photo.


That's an interesting comment Mike.

A flat tube will not affect picture size. It could certainly affect the time taken for a watchable picture but not the size. Have you tried changing the boost diode or line output valves? Either of these will affect picture size and the time taken for any picture to appear. My Fergy 45 used to take about three minutes to produce a picture. A new PY800 reduced it to just over a minute.


Cheers

 
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Re: Non destructive Tube Reactivation, Updated!

Post by crackle » Wed Oct 22, 2014 7:07 pm

please see PVP20 thread in tv's

 
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Re: Non destructive Tube Reactivation, Updated!

Post by Katie Bush » Wed Oct 22, 2014 9:15 pm

I have one nagging question that keeps turning over in the back of my mind....

How come, in amost seventy years of CRT imaging systems, it's taken until now for someone to come up with this idea? - Unless it has been tried before, but was not reliable enough, or long enough lasting, to be considered a viable method?

Marion

 
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Re: Non destructive Tube Reactivation, Updated!

Post by Terrykc » Wed Oct 22, 2014 10:24 pm

Crackle wrote:... The shadows across the screen in second picture are I believe interference patterns caused by the camera when the photo was taken, there was no such shadow on the screen ...

Mike, the problem is caused by insufficient exposure time - if you can extend the exposure time, the problem will go away.

What is happening is that the CRT is scanned once in 20mS. If the exposure is less than 20mS, some of the picture wont appear in the photograph at all.

If the exposure is greater than 20mS but less than 40mS, some of the screen will be scanned twice but the rest will only be scanned once, so the photograph will show a dark band due to underexposure.

The chances of the exposure being an exact multiple of 20mS is rather slim but the longer the exposure is, the less noticeable the difference in screen illumination time will be.

For a static image like test card, the exposure can be quite long, provided the camera mounting is stable but for moving images it is, of necessity, a compromise between movement blur and acceptable even brightness ...

This should help explain what I'm talking about - it is assumed that the aperture is set for a fully exposed picture in every case.
Attachments
Exposure.png

 
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Re: Non destructive Tube Reactivation, Updated!

Post by Rebel Rafter » Mon Dec 08, 2014 5:14 pm

Hi, everyone, I'm Rebel Rafter, from E.Lancs., I 've only just discovered this site and I've just recently joined. I found this article about non-destructive tube reactivating really interesting as I have an old Thorn TX10 stereo model, ex radio rentals, which works but still has the original tube which is now a bit flat on all three guns. I'm in the middle of fitting a scart socket to it using a circuit in "Television" magazine from October 1991, but for some reason there is no sync in the scart mode, but I'll sort that out. I think the video preamp design isn't quite right, but at the moment it's the tube I'm most concerned about. I'm going to build a "booster" like the one described on here, using a transformer from a bathroom shaver socket to provide the HT. I haven't got a crt heater transformer any more, so I'll have to put together a supply using another transformer and a regulator using say a LM338T and set it to 6.3 volts, with sufficient current. I've got a nice big 5ma panel meter to use with it on the HT side, but I've also noticed how some folk on here seem to know quite a bit more about tubes than I do. I used to do up old TV's that I got from local skips and ones that I got given back in the 80's when there was more parts available and before all that dreadful surface-mount stuff took over. I lost interest then. I was never employed as a tv engineer but I do have basic city & guilds papers. I've worked on all sorts, not just "brown" goods, so I would like to see if anyone else out there has tried using this method of tube reactivating on a 30AX tube of the 540 series. It seems from what I've read on here that some tubes need more current than others, obviously because of different cathode sizes, etc. I have done lots of tube boosting in the past, but only the old mono and big neck deltas, as used back in the 70's, but the "booster" I had was rather crude, just half-wave rectified mains followed by some big hefty resistors. I had some success with it, but I scrapped it years ago and needless to say it just stripped some cathodes, but back then there was plenty of old second hand crt's floating around, but alas not any more, so any advice would be most appreciated, thanks. I would like to keep my old BRITISH tv going as long as I can.

Yours faithfully, Rebel Rafter.

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