NBTV Television Analyst

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Re: NBTV Television Analyst

Postby Steve Anderson » Fri Apr 17, 2020 8:02 pm

Small change to ensure both counters start at the same time...hopefully eliminating that 'part-line' retrace...

A more elegant solution would be a Schmitt trigger and a cap, but this is quick, simple, and I can see you're out of board space!...and amazingly I was able to find the circuits!!!

Each time you change the line or frame rates (and power-up) I suggest giving the push-button a nudge...just to make sure...

...so, you see, I do make errors....

Steve A.

As usual, click image for higher resolution version, right click and "save image as'...
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Re: NBTV Television Analyst

Postby Harry Dalek » Fri Apr 17, 2020 10:15 pm

Steve Anderson wrote:Small change to ensure both counters start at the same time...hopefully eliminating that 'part-line' retrace...

A more elegant solution would be a Schmitt trigger and a cap, but this is quick, simple, and I can see you're out of board space!...and amazingly I was able to find the circuits!!!

Each time you change the line or frame rates (and power-up) I suggest giving the push-button a nudge...just to make sure...

...so, you see, I do make errors....

Steve A.

As usual, click image for higher resolution version, right click and "save image as'...



Thanks Steve ! i will add the changes to the Circuit that's a easy fix .
I will give that a go tomorrow ,still think the circuit is very good very useful in lots of NBTV ideas I used it in first the PMT camera then the thylacine monitor, cyclops vidicon so the NBTV Television Analyst is the 4th using this just keeps on giving :wink:

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Re: NBTV Television Analyst

Postby Harry Dalek » Sat Apr 18, 2020 7:13 pm

There's enough built now to slowly get the CRT up and running soon ,just got the heater going and like other crt projects added a switch to the heater it will help stop mistakes ! after a few more tests on its control voltages i will wire up the to the first CRT .
i can now hook the power supply board up to the CRT circuit and deflection amplifiers board ,the low voltage supply is now powering the Ramp generators .
Bit more work tomorrow ,and i did add that little change to the circuit Steve seems to work fine .
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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 » Sun Apr 19, 2020 8:14 am

Steve ,A problem that is coming up is i have kept the crts separate supply circuit wise but the cathodes would be connected around the heater connection ,would it it be wiser to not tie the vcr139's cathode to the 3bp1's mmmmm
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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 » Sun Apr 19, 2020 12:31 pm

Hmmm indeed! That is a problem. First thing that came to mind was simply using a separate heater transformer for one of the CRTs, but space and magnetic fields may be a problem.

With two different types of CRTs and two different voltage requirements there's no easy solution that springs to mind.

Possibly one of those 6V switched-mode power supplies from e-bay and the like for one CRT with an appropriate dropper resistor (if required). Don't forget the heater needs more current at switch-on than when hot. Measure the heater cold resistance and calculate the start-up current required.

I'll think on this some more...but no promises...

Steve A.
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Re: NBTV Television Analyst

Postby Harry Dalek » Sun Apr 19, 2020 2:54 pm

Steve Anderson wrote:
Possibly one of those 6V switched-mode power supplies from e-bay and the like for one CRT with an appropriate dropper resistor (if required). Don't forget the heater needs more current at switch-on than when hot. Measure the heater cold resistance and calculate the start-up current required.

I'll think on this some more...but no promises...


Don't worry to much Steve i was mainly checking if my thoughts were correct on the problem now i know it is the way forward comes down to easier solution like a second transformer or swapping the idea back to a another 3bp1 ,second transformer the magnetic field should be fine it was for the binocular monitor due to the case lay out using a vcr or dvd case the length seems to work good for the magnetic field problem on crts ,keep the transformer at distance these cases work good for the job .
Last edited by Harry Dalek on Wed Apr 22, 2020 6:29 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: NBTV Television Analyst

Postby Harry Dalek » Wed Apr 22, 2020 6:25 pm

A bit of progress ...i found the 75v zener kicked the bucket doing some tests today as to why there's no brightness control ....using that it just causes the focus to go out a bit instead of a brightness control .
I will change the 75 volt zener diode tomorrow readings across all the diodes are off ...the zener is showing a few ohms readings either test direction . (dead)
I have been running the voltages a bit lower but i can go up to -1600 and +400 if need be ...i would say the high test killed the zener ,never been lucky in the upper 1000s with that 75volt zener diode.
Well at least the deflection amplifiers are operating but here too i have do the adjustment tests see if i can even them out

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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 » Thu Apr 23, 2020 9:41 am

i changed the 75 volt zener voltage is correct 5v diode reading is not correct now and have brightness control ..but now focus is way out i will look and change a resistance here in this part of the circuit ..see how i go and post up results later today.
Last edited by Harry Dalek on Thu Apr 23, 2020 11:52 am, 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: NBTV Television Analyst

Postby Steve Anderson » Thu Apr 23, 2020 11:45 am

OK Harry. I think that this uses 3BP1 CRTs? Which may require a different span of focus voltages from whatever the original was, I don't remember. If so I'll re-calculate whatever changes are required.

Hmmm, the original was also a 3BP1...check all the resistance values around the CRT, especially any pots if they're "recycled".

Steve A.
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Re: NBTV Television Analyst

Postby Harry Dalek » Thu Apr 23, 2020 12:05 pm

Steve Anderson wrote:OK Harry. I think that this uses 3BP1 CRTs? Which may require a different span of focus voltages from whatever the original was, I don't remember. If so I'll re-calculate whatever changes are required.

Hmmm, the original was also a 3BP1...check all the resistance values around the CRT, especially any pots if they're "recycled".

Steve A.



All pots are new Steve ...power supply is different as you see the voltages on circuit load ... reducing the 220k R901 gets it in focus... but the 5.1v zener testing the voltage across it is 3 volts so it could be dead resistance across the 5v zener diode is correct .
So adjusting the temp brightness control screen gos out of focus reducing this ...
The 75 volt zener is showing 72 volt now so the 5v zener might be causing this mmm

BTW the pot shown last picture are just position size controls focus and such are trimmers i am at the moment not having them as panel controls as they should be fine once set
EDit i just found adjusting the temp brightness adjusts the 5.1 zener 5v to near zero so the zener is ok all diodes seem fine by the looks of it .
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 » Thu Apr 23, 2020 12:47 pm

The voltage across the 5v1 zener (ZD101) should stay constant whatever the brightness/focus settings are - there's still something not quite correct in there!

Steve A.

I've just looked back at the original, I now realise that you're running this CRT at a somewhat lesser voltage than before (1400v), so your change is probably valid.
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Re: NBTV Television Analyst

Postby Harry Dalek » Thu Apr 23, 2020 12:51 pm

Steve Anderson wrote:The voltage across the 5v1 zener (ZD101) should stay constant whatever the brightness/focus settings are - there's still something not quite correct in there!

Steve A.


Yes i have it on at the moment it adjusts the brightness but it gos out of focus reducing the brightness on the raster and yes the voltage range changes from 5v down i will test some more ....may be its d901 but seems ok with resistance test

Edit ...its 5v on the 5v zener with brightness trimmer reducing crt brightness to nothing ... fully on its 0.18...mmmm why is it so head scratching !
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Re: NBTV Television Analyst

Postby Steve Anderson » Thu Apr 23, 2020 1:08 pm

The CRT will de-focus at at far lesser brightness than you're probably used to on the previous 3BP1 build - significantly. Just 10% drop in the voltage will lead to a significant loss of brightness and earlier defocusing.

I've checked the datasheets for the 3BP1, really -1500v is the minimum recommended for satisfactory operation. OK, we 'got away' with -1400v last time, but that was made up by A2/G2 being at about +180v, i.e. nearly 1600v across the tube. Here it's really a bit too low. This also upsets the voltage distribution across the resistive divider chains, including 'that' zener.

It's probably time to re-think the power supply - sorry.

Steve A.

Tubes are far more fussy about applied voltages compared to semiconductors - especially CRTs.
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Re: NBTV Television Analyst

Postby Harry Dalek » Thu Apr 23, 2020 1:16 pm

Steve Anderson wrote:The voltage across the 5v1 zener (ZD101) should stay constant whatever the brightness/focus settings are - there's still something not quite correct in there!

Steve A.

I've just looked back at the original, I now realise that you're running this CRT at a somewhat lesser voltage than before (1400v), so your change is probably valid.



i have been doing a long run with it on the hv negative is now sitting on -1220 may be running in the caps .

Any case nothing over heating so that's good ...raster least keeping the crt safe .
Problems i need to fix focus ...on deflection not much position or size control since fixing the 75 volt zener this has all dropped back ..so this time not as lucky as the binocular only had one problem of focus on the second crts scope tube ...it's going to make me learn this one !
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 » Thu Apr 23, 2020 1:47 pm

Steve Anderson wrote:The CRT will de-focus at at far lesser brightness than you're probably used to on the previous 3BP1 build - significantly. Just 10% drop in the voltage will lead to a significant loss of brightness and earlier defocusing.


Ok under stood ! i have voltage control on the hv negative can go up to -1700v if need be ... problem is a little one as i have to check for voltage and temperature on the positive side ...it will increase past 400 volts positive and i have not looked into what the deflection amps can take one cap i have to smooth the positive is 220uf 400v i can remove that if need be the one on the crt A2 is rated 450 volt ..
So at the moment i was keeping mainly the hv positive in range might have to add some more high wattage resistors to reduce the hv positive dissipate some extra heat if i increase the Ac to the dc circuit ...it was originally working on 2000v so it can handle an increase.


I've checked the datasheets for the 3BP1, really -1500v is the minimum recommended for satisfactory operation. OK, we 'got away' with -1400v last time, but that was made up by A2/G2 being at about +180v, i.e. nearly 1600v across the tube. Here it's really a bit too low. This also upsets the voltage distribution across the resistive divider chains, including 'that' zener.

It's probably time to re-think the power supply - sorry.


i made it adjustable on the AC side with a saturable reactor as a had to reduce 800v ac ,thing is trying to increase a voltage is a circuit change reducing and increasing the AC is easy with this ,whats a little harder keeping the positive lower but its possible...all a bit of a challenge :roll: i like challenges ...
Steve A.

Tubes are far more fussy about applied voltages compared to semiconductors - especially CRTs.


Ok all good advice again Steve thanks always with the help ...i will give the crt what it expects and we will see what happens !
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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Harry Dalek
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