Lab guy's Bob-O-Scope

Forum for discussion of electronic television. Generally, stuff to do with CRTs and not using mechanical displays.

Lab guy's Bob-O-Scope

Postby Harry Dalek » Tue May 30, 2023 4:38 pm

Richard's building another monitor and very well worth a posting here more CRT projects the better i say .


youtu.be/yOd9uetmtsU

youtu.be/4I1X4B13VAw
Last edited by Harry Dalek on Tue May 30, 2023 9:24 pm, edited 1 time in total.
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Lab guy's Bob-O-Scope

Postby Steve Anderson » Tue May 30, 2023 5:58 pm

I've been in contact with Richard and sent him a copy of my NBTV version of this device, (Attached). He was most complimentary in his response...

Looking over it today after more than 10 years I might change a few things...

Steve A.

Note: The CRT he's using is slightly different to the one I used...basically better...though that's no excuse...

One Inch 1.pdf
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Re: Lab guy's Bob-O-Scope

Postby Harry Dalek » Tue May 30, 2023 9:33 pm

Wonder if the Monitor will fire up Steve these days capacitors are a pain in the .......to projects so you never know .
Perhaps there should be a time where you fire up your old gear just to keep it working ,i some times don't want to know as all the work you put into these things and its a toss up if you got it in time to still work .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Lab guy's Bob-O-Scope

Postby Steve Anderson » Wed May 31, 2023 3:24 pm

Harry Dalek wrote:Perhaps there should be a time where you fire up your old gear just to keep it working.

It's no bad idea, it helps keep the electrolytic caps 'healthy'. Even brand new ones from a supplier can fail if they've been sat on their shelves for years (it happens). Luckily I have a Variac, so I can wind up the voltage gently and that gives caps that haven't seen any voltage in a long time a chance to 're-form', Do a search on 're-forming capacitors', it mainly applies to electrolytic caps. There are quite a few sites concerning this.

I build things for a variety of reasons, some end up in almost daily use (e.g. a bench power supply), others are built just to create an item to be published somewhere. Once they appear in print their job is done and usually end up gathering dust somewhere. That 1" CRT item is a good example. I did it simply for the novelty of finding a use for the CRT. It hasn't been powered up in over a decade.

I recently bought two nRF24L01 modules which are basically data transceivers which work in the licence-free ISM band. First I just want to play around with them and see what they can do. One use would be RF distribution of NBTV where needed, maybe the NBTVA Convention? This time I do have a long-term intended use for them, local RF distribution of time, both local and UTC, derived from GPS. Until the demise of analogue TV, local and UTC GPS time was available in the VITC[1] broadcast via the terrestrial TV system. You may have noticed a row of 'dots and dashes' at the very top of an analogue frame. Your TV shouldn't show it as it is (was) in the overscan area of the frame which normally shouldn't have been visible. That area was also used by Teletext/Ceefax in those countries that provided it. Another use for those nominally blank lines at the top of the screen was ITS (Inserted Test Signals). While you're watching the news or whatever test signals could be inserted and measurements taken to see all is well with the transmission system...without you even knowing...

Steve A.

[1] VITC - Vertical Interval Time Code.

Below is the transceiver I referred to, the nRF24L01, I'm sure I've posted this somewhere else before...

nRF24L01.jpg
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Re: Lab guy's Bob-O-Scope

Postby Harry Dalek » Wed May 31, 2023 6:29 pm

Steve Anderson wrote:It's no bad idea, it helps keep the electrolytic caps 'healthy'. Even brand new ones from a supplier can fail if they've been sat on their shelves for years (it happens). Luckily I have a Variac, so I can wind up the voltage gently and that gives caps that haven't seen any voltage in a long time a chance to 're-form', Do a search on 're-forming capacitors', it mainly applies to electrolytic caps. There are quite a few sites concerning this.


I would think the more often the better from the time it first worked i am wondering when are we pushing our luck expecting some thing to work after a year or 2 years or 5 years.
Yes there's a bit of reforming caps tends to be out side the circuit they are in or caps never used i am wondering does it work in the circuit they are soldered in ,trying to think of a reason why not and your idea of using a Varic and reform them slowly a magnetic amplifier controlling the Mains AC to the device would be also a way adjust the AC voltage .

I build things for a variety of reasons, some end up in almost daily use (e.g. a bench power supply), others are built just to create an item to be published somewhere. Once they appear in print their job is done and usually end up gathering dust somewhere. That 1" CRT item is a good example. I did it simply for the novelty of finding a use for the CRT. It hasn't been powered up in over a decade.


I see your point i only make what i can't buy or can't afford ,i would not make a radio because i could never make one as good or as cheap ,NBTV devices not many of those in shops these days :wink: so that's my excuse ...i want the monitors i make on display and use but some times space is a problem if not in use its wrapped in plastic and boxed stop that dust problem.
As with Richard here its nice to know enough to get the idea to work complex as it is mind over matter !
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Lab guy's Bob-O-Scope

Postby Harry Dalek » Sun Jul 02, 2023 10:28 pm

The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Lab guy's Bob-O-Scope

Postby Steve Anderson » Mon Jul 03, 2023 6:38 pm

My experience tells me that usually the lower voltage elects are OK unused for a long period, but the higher voltage caps (say 200V-plus) can be troublesome. It is worth working out a simple arrangement to 're-form' them. A Variac is obviously the simplest arrangement, in the absence of that a tapped auto-transformer, but they're quite rare these days. The best alternative is a variable high-voltage DC power supply with some form of current limiting. Even if only can supply a few mA, that's enough....or should be.

For this purpose a simple audio power amplifier feeding a reverse-wired transformer should do the trick. It doesn't need to be high-powered, say a TDA2030/TDA2050 feeding a small 12VA 12V transformer in reverse...rectify the output, done. Should be be good for up to 400V caps...few these days rated for more than 450V DC...

Steve A.
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Re: Lab guy's Bob-O-Scope

Postby Harry Dalek » Tue Jul 04, 2023 12:13 am

Steve Anderson wrote:My experience tells me that usually the lower voltage elects are OK unused for a long period, but the higher voltage caps (say 200V-plus) can be troublesome. It is worth working out a simple arrangement to 're-form' them. A Variac is obviously the simplest arrangement, in the absence of that a tapped auto-transformer, but they're quite rare these days. The best alternative is a variable high-voltage DC power supply with some form of current limiting. Even if only can supply a few mA, that's enough....or should be.

For this purpose a simple audio power amplifier feeding a reverse-wired transformer should do the trick. It doesn't need to be high-powered, say a TDA2030/TDA2050 feeding a small 12VA 12V transformer in reverse...rectify the output, done. Should be be good for up to 400V caps...few these days rated for more than 450V DC...

Steve A.


Nice info i will try and remember that trick .
The Variac pretty much rare as dodo's my neck of the woods ,no one bothers with the idea but the magnetic amplifier is a very easy safe way to control a higher AC voltage
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Lab guy's Bob-O-Scope

Postby Steve Anderson » Tue Jul 04, 2023 10:43 am

Variacs are still made but they are expensive, though very useful when you need one. I bought one (new) in Singapore about 20 years ago, a smaller 300W version, which is enough for the stuff I deal with. 0-260V. I can't recall what it cost, it was some 20 years ago, so irrelevant today.

Steve A.

That Variac, still in daily use, has gathered a lot of dust.....note the binding posts/terminals, not a proper plug/socket arrangement...guess where it was made.....a clue - I had to add an earth terminal/connection to earth the metal case, there wasn't one fitted and originally it only had a two-core power cable...

Dusty Variac 1.jpg
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Re: Lab guy's Bob-O-Scope

Postby Harry Dalek » Tue Jul 04, 2023 4:45 pm

Steve Anderson wrote:Variacs are still made but they are expensive, though very useful when you need one. I bought one (new) in Singapore about 20 years ago, a smaller 300W version, which is enough for the stuff I deal with. 0-260V. I can't recall what it cost, it was some 20 years ago, so irrelevant today.

That Variac, still in daily use, has gathered a lot of dust.....note the binding posts/terminals, not a proper plug/socket arrangement...guess where it was made.....a clue - I had to add an earth terminal/connection to earth the metal case, there wasn't one fitted and originally it only had a two-core power cable...

Steve A.


I will guess its Chinese ? I can't say i have ever come across one ever .
OH they wanted you to be the earth !
I see they are still about on Ebay with mains socket this one is bit over $170 from Australia shock horror free postage ,when you have kids the money has to go else where than hobbies so i have to just look at the moment .
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Lab guy's Bob-O-Scope

Postby Steve Anderson » Tue Jul 04, 2023 5:37 pm

That version looks a lot better, though I suspect the voltmeter on the output is as good as useless. At least it should be earthed and also has a 3-pin outlet - also hopefully earthed! If it's made in China, don't count on it, check first! And also what appears to be a fuse! Amazing!! If I bought one of those I would open up the case, it looks easy to open, inspect and test before ever using it. Experience here with simple things like extension cords, multi-outlet boards, shows the internal wiring to be awful. Those red neon power switches also fail quickly, my experience again....

The version I picked up in Singapore would never have made it into Australia or the UK as it's simply too dangerous for most folk, even 20 years ago. Thankfully I hope I know what I'm doing! Well, maybe...I've had that Variac 20 years or so, and I'm still here, I guess I must be doing something right for once!

As a side-note...I would be wary, suspicious, nay scared, of All-Electric cars coming out of similar parts of the world. These things have 400V or more of high-current capable batteries. I'm in favour of the concept, but do I trust these guys? (China?) No, in one word. Surely they must have been through a tough safety check at some point on import to a reasonably safety-conscious country? (Australia, the UK and many others) And how to limit the purchasers access to the lethal voltages? It's not your 12V lead-acid battery anymore...though Joe Public might think otherwise...

Anyway, let's get back on-topic....

Steve A.
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Re: Lab guy's Bob-O-Scope

Postby Steve Anderson » Thu Oct 19, 2023 6:07 pm

I'm a little bit concerned about "Lab Guy"...he hasn't posted on his channel in around three months, rather unusual for him...also several of my postings above are also of similar age...

https://www.youtube.com/@videolabguy

He's no spring chicken, and neither am I, but the fact is noteworthy as he has dabbled in NBTV and many allied fields over the years...

This particular project of his, the "Bob-O-Scope" has seemingly ground to a halt. Any information anyone? I'll send an e-mail and report back...though I'm somewhat hesitant to do so.

Steve A.
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Re: Lab guy's Bob-O-Scope

Postby Harry Dalek » Thu Oct 19, 2023 10:46 pm

Steve Anderson wrote:I'm a little bit concerned about "Lab Guy"...he hasn't posted on his channel in around three months, rather unusual for him...also several of my postings above are also of similar age...



I think he mentioned he was having work problems or lack of it which of cause does not put you in the mood for hobbies
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Lab guy's Bob-O-Scope

Postby Steve Anderson » Fri Oct 20, 2023 11:41 am

Well, let's hope that's the case and not something that's really bad news...

Steve A.
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Re: Lab guy's Bob-O-Scope

Postby Harry Dalek » Sat Oct 21, 2023 3:40 pm

Steve Anderson wrote:Well, let's hope that's the case and not something that's really bad news...

Steve A.


Yes fingers crossed for sure didn't cross my mind he could be ill or worse
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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