Re-Activating early, failing, CRTs

[Edward Huggins]

I just can't remember what we called it (was it RE-ACTIVATE?) when we re-boosted failing early rectangular CRTs (usually pre-Aluminumised) c.1954/55 with a simple circuit that re-coated the electrodes to brighten older, used, low-luminance, tubes.
In fact the procedure could be repeated ad-infinitum until the old CRT gave out it's last gasp. This was from a Practical Television circuit and they could be bought pre-assembled as well.
Don't laugh, in those days one could buy "used", re-claimed TV tubes for quite a low price and get a longer life out of them. We used it to prolong the life of our Masteradio T917, 5 channel TV from 1954.
Now how many of you out there can remember this dodge! Edward

[TonyDuell]

From where I am sitting I can see my BK model 467 'Picture Tube Restorer/Analyser', one of the functions of which is to just that by over-running the heater and applying a high voltage between cathode and grid (I think).

I don't know when this instrument was made, but I would guess early 1970s given that it uses a valve, discrete transistors and TTL ICs (on the same PCB).

[music-centre]

Like a lot of other Forum members must have done, I made one of the Practical TV magazine Tube boosters ( mainly because there were only half a dozen bits to it!) 100W bulb for the heater, I think, a Diode and a couple of resistors with a red pygmy bulb to show it was doing something when you pressed the switch.

It was actually very effective, I tried it on our old PYE 169 black and white set that hardly showed a picture and it came up as bright as new - for a while anyway!
Steve.

[Nuvistor]

I don't think it recoated,rather strip a layer of dirt or exhausted cathode material off. Yes I remember, rarely used it though, tended to use a boost transformer. Some CRT faults were heater cathode shorts so the special low capacity between windings of a boost transformer set at 1:1 cured those as well.
Frank

[Cobaltblue]

I have bopped a tube or two especially back in the early 70's when 50's sets were available for pocket money but still made great second sets.

However it was kill or cure

Cheers

Mike T

[peter_scott]

I was recently chatting to an ex-tv repair man and he told me that re-activation was much more effective if the tube was positioned with the screen uppermost and neck vertically down. The explanation being that the cathode surface becomes molten during the process and the vertical orientaion of the gun assembly ensures that the material remains nicely centred. He also said that it's best to maintain the heater voltage and vertical orientation for a good few minutes after re-activation.

Peter

[Clydeuk]

I remember an old Philips set in the 1990's with a really flat tube, when I took the back off to look inside I noticed an engineer's label stating the CRT had been "cathodised" and the date it was done. Quite obviously boosted, was this one of those terms that engineers used so the customer wasn't aware of the real truth?

One dodge we used to do for heater-cathode shorts in later sets that would otherwise have needed a CRT was to disconnect the heater from it's original supply, wind a couple of turns of insulated wire round the limb of the LOPTx and feed the heater from that (can't remember how many turns - we used to gauge it by how bright the heaters looked). We would inform the customer of what we had done and the reason why, and only charged a token amount. I know of one set that was still running happily this way 2 years down the line.

[slidertogrid]

I used a home built "Bulb Bopper" on mono tubes and delta gun colour with great success. The only time a tube wouldn't respond was if it had been blasted too hard by someone previously.
I used a Rank A640 frame transformer for the heaters as suggested in "Television" magazine at the time I built it. I found the best method was to overrun the heaters when boosting and then switch off the heaters with the HT still applied until the sparking stopped.
PIL and 20AX tubes didn't respond as well I found the best way with those was to overrun the heaters slightly by lowering the value of the series resistor or in the case of Pye/Philips slightly shorted one of the heater chokes. The way to make it last the longest was to go just enough to improve without making the heaters too bright.
The "mod" for the G11 worked very well but as it had no series resistor it was a bit more involved..
This was mainly used on our own sets to squeeze the last out of them as cheap low end rentals. The tube would usually last until the set clapped out.

[Welsh Anorak]

Hi
I always found that for the reactivation to 'take' it was necessary to switch the TV on as soon as the booster was disconnected. This could result in a few fireworks in the neck!
It was aways a good idea when visiting an ex-rental warehouse to have a look around for a well-used reactivator on the bench as that set you just bought might not have a sparkling picture for long!
I still have a couple of BK 467s in the workshop plus an old Leader one and a home-made 'Television' project. However after the arrival of PIL and 20AX, boosting never seemed to work - and it never did on Trinitrons.
Glyn

[TonyDuell]

I must admit that the reason I have a BK467 (other than it was a fiver at a museum sale...) is for testing CRTs. Useful to know that all 3 guns in a colour CRT are doing something, for example. I am not sure boosting is ever going to really help me...

BK did list some Trinitron tube adapters for this unit. Whether you ever got any useful results attempting to boost such CRTs I do not know.

[MrBungle]

Not much of a CRT person really but I'm wondering if this could have been why my parents' Grundig set had black spots on the phosphor after a hooky repair job by a friend of the family.

[Nuvistor]

Was that a B/W or CTV? Don't know what would cause that after a repair but I keep a very open mind on these things nowadays, anything is possible.
Frank

[Hunts smoothing bomb]

I know some people rejuvinate the crt with it in the face down position, their argument is that any debris that is blasted from the cathode during this process ends up away from the electrode structure in the neck, one downfall of course is that it can become trapped in the mask where a colour crt is concerned and can prevent the electron beam from reaching its relevant phosphor thus showing up as a black dot when the set is displaying content on screen. I have seen this before on a colour receiver.

Cheers

[MrBungle]

Originally Posted by Nuvistor

Was that a B/W or CTV? Don't know what would cause that after a repair but I keep a very open mind on these things nowadays, anything is possible.

This was B/W. This happened around '81 and the set was early 1970 latest. Not quite as vintage as some of the stuff on here.

Edit: may have been earlier than that. My father said, via SMS, it had valves in it and they bought a Sony to replace it because it was a (expletives removed)

[Welsh Anorak]

Sounds like bits could have fallen onto the phosphor, though I've never had that happen, even though I used to clean and balance CRTs with the set lying on its face. Re post#6, I've never heard of boosting with the CRT that way up but it does make sense.
The clean and balance function was very handy on the BK as it could rejuvenate a slightly low gun which didn't really justify a new CRT, and didn't have the Russian roulette gamble of a full rejuvenation.
Glyn

[Panrock]

Just to throw my recent experience into the pot... I was disappointed with the MW31-74 in the Bush TV24A (the donor chassis for my "Bude" Bush-Baird combo).

Since the tube heater feed on this combo used a separate mains transformer + series resistor, it was simple to boost the tube heater voltage by 10% and run it like this for 6 hours or more (estimate: I didn't count).

This woke it up good-and-proper, resulting with a 'new tube' like picture. After that, I put the heater voltage back to the correct value and the improved performance was maintained.

I am hoping I burned some crud off the cathode and/or maybe woke up the gettering and the tube will now be good for years of further life.

Steve

[Edward Huggins]

What a super photo story on the unique BUDE, such attention to detail and such patience! As for the Tube reactivation, you may find it may not last for "years" and so will need the odd 10% extra burst from time-to-time to maintain brilliance. Edward