NBTV Television Analyst

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Re: NBTV Television Analyst

Postby Steve Anderson » Thu Apr 02, 2020 8:20 pm

I suggest adding a resistor in parallel with each 450v cap to help equalise the voltage across each cap, say 1M/1W. Then the voltage across each one should be less than their rated voltage. They also may take some time to 're-form', a process that an electrolytic cap requires when not exposed to a voltage for a long time.

If you have a source of 110/115v start off with that for a few hours, then apply 220/240V. If you have a Variac, even better still...but not many do.

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Re: NBTV Television Analyst

Postby Harry Dalek » Thu Apr 02, 2020 10:02 pm

Steve Anderson wrote:I suggest adding a resistor in parallel with each 450v cap to help equalise the voltage across each cap, say 1M/1W. Then the voltage across each one should be less than their rated voltage. They also may take some time to 're-form', a process that an electrolytic cap requires when not exposed to a voltage for a long time.

If you have a source of 110/115v start off with that for a few hours, then apply 220/240V. If you have a Variac, even better still...but not many do.

Steve A.



OK Steve that is a plan to work with , i do have a 100 volt Ac supply and 200 to do this after so i will work those capacitors in /

I will add the resistors to equalise the voltage also .

I am not used to working this high an AC voltage , but this transformer does have benefits on the other low voltage supplies ,just means i have to change things on the HV supply side ...and work safe of cause ...

Thanks Steve i trust your advice gives me confidence very much so when working on power supplies !
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Re: NBTV Television Analyst

Postby Klaas Robers » Thu Apr 02, 2020 10:14 pm

This is impossible. You should get about 600 volts with this circuit. So:
- or the 400 volt AC is much more, say 1200 volt,
- or your misread the voltmeter(s),
- or you have used a different circuit than you have been drawing.
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Re: NBTV Television Analyst

Postby Harry Dalek » Fri Apr 03, 2020 8:01 am

Klaas Robers wrote:This is impossible. You should get about 600 volts with this circuit. So:
- or the 400 volt AC is much more, say 1200 volt,
- or your misread the voltmeter(s),
- or you have used a different circuit than you have been drawing.


The transformer was originally from a 80s video disc player with a neon helium laser the windings read around 900 v AC , 14 0 14 and 7.2 ...not sure what the 7.2 volt was for the laser didn't have a heater.

But i agree on the voltage result i will double check ,some times meters can misread very much so on high voltages.

I was checking all this with a few meters for the same result yesterday but double check today
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Re: NBTV Television Analyst

Postby Steve Anderson » Fri Apr 03, 2020 12:56 pm

If the transformer is really 900V AC on the output one would expect about 1270V from a simple rectification arrangement as shown with no load. You're quite correct in ensuring the caps are rated for the job, but check the diode(s). They need a reverse rating of at least 3kV! Not that many around like that!

With a load (which probably was very light originally) that figure could come down significantly. If the transformer is quite small, i.e. it fits in the palm of your hand it definitely would have been a light load, but a CRT with a suitable circuit is a light load too.

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Re: NBTV Television Analyst

Postby Harry Dalek » Fri Apr 03, 2020 1:37 pm

Steve Anderson wrote:If the transformer is really 900V AC on the output one would expect about 1270V from a simple rectification arrangement as shown with no load. You're quite correct in ensuring the caps are rated for the job, but check the diode(s). They need a reverse rating of at least 3kV! Not that many around like that!

With a load (which probably was very light originally) that figure could come down significantly. If the transformer is quite small, i.e. it fits in the palm of your hand it definitely would have been a light load, but a CRT with a suitable circuit is a light load too.

Steve A.



Hi Steve I double checked this morning with all my multimeters i found my main one is misreading all those are showing around the 800 mark AC on the HV coming out of that Transformer .

The simple way to get dc here i connected the circuit to the a 100 or so volt ac supply from another ac power supply giving a nice 140 volt dc with the 1m resistors across all 3 caps .

I then swapped to the 800 volt ac i thought well it 100 ac is giving 140 v 800 should be around 1120 v but it does not work you can hear a slight buzz from the transformer and its not rising as it should in voltage so disconnected that quick ...i could only think it was the diode but it worked fine on the 100 volt supply i added a second in series but still not good ....reading your reply it should have a 3000 v rating i do have microwave diode handy or 3 or 4 1000v diodes series ?

I am looking into this right now .

The transformers the one in the photo a few post back its big like a valve transformer ..Its got BANDO VTT 018 if that means any thing ...

i will try and work on the diode side of it see how it go's and post up .

EDIT ....1070 v with 3 1000 v diodes in series very happy ...transformer no sound every thing seems fine ....its hard using high HV AC like this , i still have to double this as its still to low for the 3Bp1 CRTS but not the pmt ...if its about 1600 or above i will have sparking problem if i construct the power supply incorrectly so i would have to take this into account when constructing .
Also its a 2 winding transformer bit more tricky to get the positive dc may be i can add a little transformer and tap the 14v or 7v ac supply to get a higher ac voltage and use that ....just leave the HV AC supply for the high negative supply voltages for now ..
Last edited by Harry Dalek on Fri Apr 03, 2020 5:46 pm, edited 2 times in total.
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Re: NBTV Television Analyst

Postby Steve Anderson » Fri Apr 03, 2020 2:42 pm

One way around the 3kV rating required of the diodes used in a half-wave rectification circuit is to use a bridge rectifier arrangement, then in this case they would only need a 1500V rating. It also improves regulation and reduces ripple...for the cost of only three extra diodes. However, it isn't as easy to produce both positive and negative supplies at the same time...if needed.

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Re: NBTV Television Analyst

Postby Harry Dalek » Fri Apr 03, 2020 3:29 pm

Steve Anderson wrote:One way around the 3kV rating required of the diodes used in a half-wave rectification circuit is to use a bridge rectifier arrangement, then in this case they would only need a 1500V rating. It also improves regulation and reduces ripple...for the cost of only three extra diodes. However, it isn't as easy to produce both positive and negative supplies at the same time...if needed.

Steve A.


Yes i would be happy with the 1500 range ...i will make one taking into account now i know how to handle the idea ,yes that's a good idea !

I will worry to about the positive anode supply later i think i can do it another way .

So i would just need a doubling of diodes in the bridge idea that's still fine ,as you say a cleaner DC supply too ...at 1500v i would add another 450 v cap at the end ....oh well give it a go .
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: NBTV Television Analyst

Postby Harry Dalek » Fri Apr 03, 2020 5:39 pm

I ran out of time today to make the bridge rectifier circuit ,instead i worked on mounting neatening up the power to the Transformer supply and powering it so that's done .
Things will go quicker now i can work on the power supply board...working with these voltages i like it neat and have the HV disconnected safely out of the way till i need it that way can't get shocked if it isn't there ! so gets connected when testing then removed .
The board closest to the Transformer is going to be the power supply board .
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Earlier today checking my meters on The transformers HV just shows you they are close but never the same.my main meter was just plain faulty way out lucky i have more than one to check ...
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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: NBTV Television Analyst

Postby Steve Anderson » Fri Apr 03, 2020 6:55 pm

With meters it's always best to buy the best you can afford. It's also said of time, "A man with one one clock knows what the time is, the man with two clocks is never really sure." The same applies to any test instrument. Buy the best you can afford and throw the rest away. Seriously, I only have one meter that I trust 100%...and it's not a high-priced Fluke - as attractive as they may be.

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Re: NBTV Television Analyst

Postby Harry Dalek » Fri Apr 03, 2020 7:52 pm

Steve Anderson wrote:With meters it's always best to buy the best you can afford. It's also said of time, "A man with one one clock knows what the time is, the man with two clocks is never really sure." The same applies to any test instrument. Buy the best you can afford and throw the rest away. Seriously, I only have one meter that I trust 100%...and it's not a high-priced Fluke - as attractive as they may be.

Steve A.


Yes i like that idea i am a sucker for a multimeter reason i have a few :roll:
The old meter shown Micronta (Tandy) Digital Multimeter Model 22-198A must be close to 40 years old and still works fine never manged to kill it and thats saying something !
wishful thinking i think below
https://articulo.mercadolibre.com.ar/ML ... -instr-_JM

What brand do you use Steve ? just in case i can leave the door step for a virus free trip to Jaycar one day in the far future !
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: NBTV Television Analyst

Postby Klaas Robers » Fri Apr 03, 2020 8:03 pm

In our technology we seldom need a better precision than 10%. So all meters that you have show 800 volt, that is between 720 and 880 volts. A Delft-collegue of mine always said: "the first number and the place of the decimal point". But I have read on your drawings your 9 (900 volt) to be a 4 (400 volt). That is a problem of hand writing...... For me a nine should be closed at the top.

Harry, when you do things with high voltages on, ALWAYS work with ONE HAND. Place your other hand behind your back, I always grip the back edge of my throusers firmly. And see that you wear shoes with rubber or plastic soles. Then you only can be shocked at your working hand, which is painfull but not too dangerous. And if possible switch off the circuit before you are going to do things and wait long enough to discharge the capacitors. In several tube equipment I mounted a small neon lamp on the mains input and on the high voltage, with a resistor in series of course, say 220k. Then you see that something isn't safe, when the little lamp is on.
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Re: NBTV Television Analyst

Postby Steve Anderson » Fri Apr 03, 2020 8:43 pm

Yes, handwriting. As most of those here will notice - I never use it - mine is worse than a doctors! Some notes I may have scribbled the day before I cannot read myself the next day. I'm a big user of Notepad - just to write notes/reminders to myself. Or on the 'phone, just to remind me of such-and-such. Being left-handed (except for writing - it was literally beaten out of me as a kid) I am pretty much ambidextrous..which really did help with playing piano...

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Re: NBTV Television Analyst

Postby Harry Dalek » Fri Apr 03, 2020 8:59 pm

Klaas Robers wrote:In our technology we seldom need a better precision than 10%. So all meters that you have show 800 volt, that is between 720 and 880 volts. A Delft-collegue of mine always said: "the first number and the place of the decimal point". But I have read on your drawings your 9 (900 volt) to be a 4 (400 volt). That is a problem of hand writing...... For me a nine should be closed at the top.


Sorry about that my messy writing Klaas ! and i was believing a faulty meter so start again the AC is around 800 volts

Harry, when you do things with high voltages on, ALWAYS work with ONE HAND. Place your other hand behind your back, I always grip the back edge of my throusers firmly. And see that you wear shoes with rubber or plastic soles. Then you only can be shocked at your working hand, which is painfull but not too dangerous. And if possible switch off the circuit before you are going to do things and wait long enough to discharge the capacitors. In several tube equipment I mounted a small neon lamp on the mains input and on the high voltage, with a resistor in series of course, say 220k. Then you see that something isn't safe, when the little lamp is on.

[/quote]

That's good advice for sure these voltages are dangerous... when test is over on the last few of these builds i test the High DC voltage till its gone and disconnect the AC ..Yes i have to put in a light on indicator .. i will have to be testing low voltage circuits so if not needed best have the 800v disconnected from the DC side via the below you will see it next to my transformer.....i will see what i can find for an on indicator as it does help .
I always find its more on my mind this sort of thing when i am building with high voltages some one who just works with low dc supplies you really have to change your way of thinking . I don't want to be John Logie baird and hes 2000 volts Battery mistake didn't loose he's life a wonder but lost he's home !
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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: NBTV Television Analyst

Postby Harry Dalek » Sat Apr 04, 2020 12:24 pm

I have constructed the Bridge rectifier
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Results are i took the readings as + was ground so maximum voltage is 1080 very similar results to the single diode may be the extra cap and resistor in the chain ?

DSCN6301.JPG


This as is would be fine for the PMT ...still to low for the CRTS might have to try a voltage double version even an extra 400 would be good... since i am grounding the positive just using negative a doubler circuit over this using the same Ac supply work ? ...other wise i think i will have to start again.

Might just knock one up wire connecting the parts off board see what the results are as using one on its own ...

Any its all working fine just a bit low result wise ...i rather that than parts heating up and such !
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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