[Atif] is quite fond of his custom Oscilloclock Model 1, originally supplied with a bright green Brimar SE5F/P31 CRT. He just loves its crisp, clear trace! But wouldn’t it be great if he could plug-and-play a different CRT, to suit his mood of the day?
More specifically, could I create a second display unit (the acrylic tube on the left) using a CRT with a soft, long-persistence blue trace? And could he just swap the units around at will, without having to make any changes to the control unit?
Absolutely! But to make the 2nd unit completely compatible for plug-and-play, we’d need the same SE5F type CRT, with a different phosphor. Looking at Brimar’s catalogue, this CRT was available in several phosphors – including a P7 blue. This is the same as used in the original Prototype, and it’s really good at showing off those exotic trailing effects!
So the hunt began…
Now, this particular P7 CRT is famously difficult to come by – whether new OR used.
The most common piece of old equipment employing the SE5F was the ubiquitous Telequipment S51 oscilloscope, but the overwhelming majority of those had a P31 phosphor CRT installed. Indeed, of all the demonstrably working S51’s posted on eBay in the past decade, I have never seen a single one showing an obviously blue trace!
After many months of scouring auctions, suppliers and CRT fanatic colleagues across the globe, I managed to locate one SE5F/P7 in highly questionable condition – and located in Italy! With Google Translate as my friend, negotiations ensued, and – taking a substantial risk that the CRT would actually function – the unit was duly purchased and shipped.
Often, well-used CRTs exhibit scratches, spots, or burn-in marks on the internal phosphor coating. Fortunately, this CRT’s phosphor proved unblemished! And powering it up (for the first time in decades, most likely), it proved to be electrically faultless, as well!
Beautifying the Brimar
You may think that cleaning a CRT is hardly worth writing home (or the world) about.
But this specimen was slathered in sticky, gooey tape residue, which had to be carefully removed. My chemical of choice for this is, believe it or not, eucalyptus oil! Not only does it remove the gunk, but it also serves to clear up any nasal or bronchial congestion that the technician may have at the time. Two birds with one stone!
The more difficult issue was removal of the graphite coating. During manufacture, the front-most 8 cm of the glass of each SE5F was sprayed with a conductive graphite-based paint. Why? To make a high-voltage capacitor with the spiral accelerator anode (the beautiful green stripes) and similar graphite coating on the inside of the glass. By connecting the external coating to ground, the thrifty circuit designer could avoid using a separate (and expensive) high-voltage filter capacitor in the anode power supply!
Why remove this coating? Because during use, it gets scratched and marred, as the above photo shows. Such a messy CRT could never be worthy to mount in a clear cast-acrylic case for an Oscilloclock! In addition, the coating obscures some of the attractive spiral accelerator anode, and blocks the incredible view of the trace from behind. And regarding circuit design, we at Oscilloclock NEVER scrimp – the Power Board has oodles of filtering capacity without relying on a graphite coating!
While eucalyptus oil is also effective, it can get rather expensive in the quantity required – especially as the Oscilloclock lab is not conveniently located in Australia! The more reasonably priced chemical of choice here is nail polish remover. As always, there is a side-benefit – the nasal passages are assuaged by a delicate floral scent during cleaning, and fingers have an arguably nice smell that lingers for quite a while!
Joking aside – gloves, open windows, good ventilation, and safety glasses (in case the CRT implodes) are key ingredients for this process!
Having found the perfect CRT, [Atif]’s plug & play unit is now well under construction.
Epilogue – “Good things come in threes”
It’s not good just getting one CRT. What if [Atif] wanted a spare? What if I wanted a spare for my venerable Prototype clock? Following from the Italian success, I continued a further 6-month hunt, and managed two achievements.
The first was a Telequipment S51b unit located in the U.K. that was non-functional, but that I suspected may have a P7 phosphor installed. How could I possibly suspect this? Well, perhaps this is an art rather than a science, but there were several tell-tale signs:
The way the phosphor looked under the camera flash or ambient light
The colour (or absence) of the graticule (the plastic cover in front of the CRT)
The fact that I got a double when I rolled the dice to decide whether to take the plunge or not!
The seller of this unit was not willing (or perhaps not technically able) to extract the CRT, check the CRT type, or ship overseas. Fortunately, my colleague in the U.K. was more than happy to receive the scope at his end. Thus arranged, when the unit arrived he extracted the CRT and confirmed that – sadly – I had purchased a P31 CRT.
But I shipped it across anyway, and the CRT tested well. Rescuing a functional SE5F/P31 from eventual demise was still a worthy accomplishment!
The second achievement was prompted by an auction listing for a “Brimar SE5F”, but with little indication as to the phosphor. The photos of the label (see right), even with subsequent close-ups provided by the seller upon request, were not conclusive.
The image shows two characters beginning with ‘P’. It looks like “P1”, which is another extremely common green phosphor used in many CRTs since the beginning of time. However, we saw in the catalogue earlier that Brimar only supplied GV, P7, P31, and P39 phosphors as standard. It is unlikely that any equipment manufacturer would have requested Brimar to produce a custom CRT batch using the less-exotic P1 phosphor… Leaving the P7 as the only likely candidate!
Convinced, the CRT was duly shipped across and tested – and lo and behold, success! A spare P7 was safely procured.
And with that, the long saga of this CRT hunt closes. As they say, “good things come in threes!”
Like what you see?
Cathode ray tubes used to be manufactured in all shapes, sizes, and colours. Some prove harder than others to find! But if you prefer an exotic creation, don’t give up – there is something for you out there, and here at Oscilloclock we will find it.
As always, see previous posts and the Gallery for info on unique creations!
When I first heard from [Masahalu], a local artist and woodwork craftsman, I had a hunch that Oscilloclock history was about to be made.
His request initially seemed simple; he wanted an Oscilloclock Core – a bare-bones board and CRT assembly, which he could install into a case of his own design.
However, he wanted something totally unique. Something old, yes, but also something new. The artist in him demanded a different canvas of creativity.
Presenting Masahalu’s new canvas: A 5″ amber CRT Oscilloclock!
The new-old-stock CRT shipped with this unit features a P12 phosphor, and was originally produced for use in radar equipment. The phosphor’s long after-trace (persistence) allows for some fascinating ‘trailing effects’ in the Oscilloclock’s various animations.
Those familiar with CRT phosphors may point out that P12 is often classified as an orange phosphor, not “amber”. To my eye, though, the soft, warm trace of this CRT is better associated with eons-old fossilized tree resin than the sharp, bright color of fruit.
Amber CRTs are quite rare, especially in larger sizes. 3-inch P12 CRTs can be found, but the Oscilloclock Lab was fortunate to find several of these rare 5-inch CRTs.
[Masahalu] has certainly ended up with the unique canvas he requested, and we look forward to seeing what kind of case design he ends up with!
Like what you see?
It’s so much fun letting these cathode ray tubes shine their colourful rays again! Whether you’re into yellow, amber, blue, white, or just plain green, there is something here for you. Visit the Availability page for more information, and of course see the Gallery for other unique creations!
Many folks have asked whether screenburn-in, or phosphor burn, is not a problem. They are concerned by what was a frequent occurrence in the CRT monitors and oscilloscopes of yesteryear: a permanent scar prominently visible on the screen…
Phosphor burn – this old spectrum analyser looks ‘on’ even when it’s off!
To understand why this occurs, first think of an iron burn. If you deliver too much heat for too long into the same spot, your nice new Oscilloclock brand T-shirt will feature a prominent (and permanent) mark as shown below.
Iron burn – this shirt’s fibres have been literally scorched!
(I could push for another analogy, and describe livestock branding – but I think you get the message.)
In a CRT, a beam of fast-moving electrons bombards the phosphor coating on the screen to produce an image. If the beam is too intense, or it is allowed to trace the same route on the screen over a long period of time, the phosphor compound may degrade and lose its luminance. The end result is:
The screen won’t light up well in those spots any longer.
The damaged areas may appear dark even with the power off – a ‘ghost image’.
Interestingly, this damage does not actually shorten the working life of the CRT! (It does not affect the longevity of the heater, or the amount of gas permeating the vacuum.) However, it is certainly not attractive, and is most definitely NOT an effect you wish to observe on your fancy custom-crafted Oscilloclock…
Keeping the ghosts at bay
Happily, screen burn-in is not much a problem with the Oscilloclock. Let’s see why.
1. CRT selection
Some CRT types and brands are more susceptible to screen burn-in than others. There are a number of factors for this, and all of these are considered during CRT selection to minimize the risk of burn-in:
First, there is the phosphor compound used. Some phosphors, just by their chemical makeup, degrade faster than others. More significant, though, is the fact that some phosphors require more energy (electron beam intensity) to produce the same level of visible light output as others.
For example, a long-persistence blue P7 phosphor, such as used in the Model 1-S and the Prototype, is by its nature ‘darker’; it requires a higher beam intensity than the crisp green P1 or P31 phosphors used in many other models. The higher beam does make the P7 more vulnerable to burn-in.
Different phosphors need different intensities to appear ‘bright’ – so some will burn faster
Fortunately, the simple protection mechanisms in place in the Oscilloclock (we’ll get to these later) will avoid burn-in even on sensitive phosphors. The customer need not be concerned about this risk factor, and can select any of the available phosphors.
The second factor is the thickness of the phosphor coating. The thicker the phosphor, the less burn-in for the same beam intensity. Some CRTs are infamous for having ridiculously thin phosphor coatings, making them extremely susceptible to burn-in. Sadly, some CRTs that are most readily available today fall into this category, and their data sheets even specify an incredibly short maximum longevity of 1000 hours. That’s less than 2 months of continuous use!
Beware CRTs with short lifetime ratings – they may have ridiculously thin phosphors!
Most CRT manufacturers did not publish lifetime ratings, nor did they publish specifications of phosphor thickness. In the Oscilloclock lab, I rely mainly on my and others’ experiences with the manufacturer, and pick and choose only the highest-quality CRTs. Expensive – but definitely worth it!
The third factor is the use of any additional technology in the CRT that would allow for reduced beam intensities. The most common example is the aluminized screen, an additional coating on the rear of the phosphor. This coating reflects the light that would normally emanate from the phosphor towards the rear of the CRT, back into the phosphor (and the front of the screen). A much more efficient use of energy!
However, this technology was a later development, so many CRTs with an aluminized screen tend to be rectangular and have an in-built graticule. These may not be as visually pleasing in a standard Oscilloclock as non-aluminized CRTs.
2. Software (Firmware) protection mechanisms
Remember the phrase “screen saver”? In the pre-LCD monitor days, most computers employed some form of software that would stop the same image being displayed for too long, to avoid screen burn-in.
My favourite screensaver – Flying Toasters! (Image used under Fair Use terms)
While there is nothing as fancy as flying toasters, the Oscilloclock has several mechanisms in place.
Hourly XY Bump screen saver
This feature simply shifts the image by a small amount in the X and Y directions every hour. The shift pattern repeats every 31 hours (a prime number), to ensure that every hour numeral will be placed in every screen position.
Auto screen switch
This feature simply cycles through the screens (clock faces) at regular intervals, configurable from 0 (off) to 90 seconds. This is by far the most commonly enabled feature, as it allows one to enjoy all the Oscilloclock screens without touching the control!
Auto power off
Strongly recommended by Oscilloclock labs, this feature simply turns the Oscilloclock off after a period of non-activity (not touching the control), configurable from 0 (off) to 90 minutes.
This may sound counter-intuitive, but in practice, nearly all Oscilloclock owners are comfortable to turn their unit on just when they intend to enjoy it, and allow it to switch itself off. The exceptions are clocks that are permanent fixtures in offices and restaurants, in which case the owners manually turn their clocks on and off together with other appliances in the premises.
These features are of course highlighted in the Operation Guide that accompanies every Oscilloclock.
Summing it up
So there we have it – there’s not so much to be concerned about after all. While CRTs do have a delicate phosphor coating, by selecting a decent CRT in the first place and looking after it in use, the risk of screen burn-in is drastically reduced. In fact, in 7 years of constructing Oscilloclocks, as of today not a single unit has come back for a CRT replacement!
Humpty Dumpty sat on a wall…
Humpty Dumpty had a great fall…
…and so the great nursery rhyme goes! But here at Oscilloclock labs, we’re not talking about an egg (which, one theory goes, represented the defeated King Richard III). We’re talking about a beautiful old CRT, savagely shaken and shattered during international shipping. What a waste. But oh, what a great chance to see the insides close-up!
This broken CRT missed its chance to live again in a nice VectorClock
Looking down the barrel. Imagine you are a phosphor molecule, with projectiles from this gun hitting you at the speed of light!
What do you do on a mundane business trip to London?
Why, shopping, of course! But if you were the humble proprietor of Oscilloclock.com, you would do much more than that… You would seek to expand your vintage electronic empire!
And so it was that I found myself hunting old electronic devices on Portobello Road one fine Saturday morning. Unfortunately, the game there was far and few between; only two relatively mediocre valve radios, in even more mediocre shape, at far more than mediocre prices…
Fortunately, my colleague was going to save the day. “Pop out to Cambridge for a visit – I’ve seen a few antique shops here,” said he. And after the hour train journey and a wee but of walking, we stumbled onto a veritable gold mine – Robbie’s.
Yes, you’ve all thrown away your lunky old CRT monitors, in favour of sleek ultra-thin LCD displays. And, you thought you’d never see another one again…
But this CRT display has a twist! It’s round. It’s small at just 3 inches diameter. And it’s awfully cute.
Last year, I was approached by a dedicated flight simulation enthusiast, who needed a radar indicator to use in a fighter cockpit replica. The indicator should employ a CRT, for the most realistic look. Could Oscilloclock design and construct such a display?
It didn’t take much convincing! Diverging only temporarily from building clocks, I took up the challenge to create my first raster-scan CRT display unit. In the ensuing months, difficulties sprang forth from every direction in the project, but ultimately I was able to avoid a diraster (sic) and deliver a functional assembly:
The key component of this setup is a new prototype VGA Board that converts a VGA signal into analogue X and Y outputs. Both analogue intensity and binary blanking outputs are provided.
Oscilloclock VGA Board prototype
The X and Y outputs drive an Oscilloclock Deflection Board, while the binary blanking output drives the blanking amplifier in a CRT Board.
Deflection Board – modified for ultra-linear HV output
CRT Board – modified for improved frequency response
Blanking isolation, heater, and HV supplies are provided by a Power Board.
Power Board – with improved optocoupler
It all looks so easy! But noooo. Astute readers will recall from other posts that every Oscilloclock project involves sleepless slumbers, horrific hair-pulling, and forgotten family members. Let’s see what caused me grief this time…
One of the most exciting things you can do with a Scope Clock is to simply look at it from behind! In many CRTs, the anode coating (a conductive black surface sprayed onto the inside of the glass) doesn’t extend all the way to the screen – leaving a nice gap of clear glass from which to observe the beautiful electron beam.
Ha – you can put down your magnifying glasses now.