The Tasmanian Devil VCR139....A for Andrew

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Re: The Tasmanian Devil VCR139....A for Andrew

Postby Harry Dalek » Sat May 27, 2017 8:24 pm

Steve Anderson wrote:Harry, I think this should be about right. As the tube runs on a lower voltage than the 3BP1 the bias needs reducing, so the 75V Zener is now 24V. All changes from the 3BP1 arrangement have been marked in red...quite a few.


Oh thanks there Steve boy your quick ! no wonder your good at all this !
Those changes are not to bad i was always wondering about that 75 volt Zener but i also was interested to see what would happen as is .

Also as a lower-voltage tube the deflection sensitivity is higher so we may need to reduce the gain of the deflection amps, but we'll worry about that when we get there. Only two resistors in each deflection amp would need changing.


Thats also not to bad well designed circuit indeed .

Also for the 'AC on the plates test', use a centre-tapped transformer, centre-tap to pin 9 and the two others to (say) pins 11 & 7, Connect pins 8 & 10 direct to pin 9. This is only temporary. This should give you a straight line across the tube.

Steve A.

[/quote]

Well that would not of crossed my mind so thats a procedure i i will remember !

Thank you Steve i wish i could get out to the shed and do the changes tonight ...also tomorrows a big 40th birthday for my brother inlaw so no soldering for me :( very keen to do the changes may be early in the new week ..
BTW i was looking at the investigator Scope about the only schematic with voltage points shown .
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Re: The Tasmanian Devil VCR139....A for Andrew

Postby Klaas Robers » Sun May 28, 2017 7:36 am

Harry, have you in your experiments conneted the deflection plates to any voltage? I would connect them to about the highest positive voltage. If not they can be charged by negative electrons and that will any way affect the result on the screen.

Steve, what would you do in this case?
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Re: The Tasmanian Devil VCR139....A for Andrew

Postby Harry Dalek » Sun May 28, 2017 10:54 am

Steve Anderson wrote:Re-reading a previous post regarding the voltage across the opto-transistor, this should stay relatively constant at around 4.2V (ish) so have a poke around there. First though change items noted in posting above.

Measure cathode to grid of the CRT, with the CRT off, this should vary from approximately 0 to -24V relative to the cathode...with the new 24V zener fitted.

Steve A.


HI Steve
Happy to report i have first light :D
We ended up not having to go out today till midday so i had a early morning electronics fix ...
Across the control grid and cathode it varies from 0.4 to 23.6 volts ..
The 5 volt zener the original one in...... i did a 1k 12 volts test with it it was showing 0.8 must of be a dud same test with a new zener i was getting 4.7 volts so i used that .
for the 24 volt zener i used 2 12 volt zeners in series that worked well .
Also the AC supply on the deflection plates i used a 6.7 0 6.7 volt transformer suppose why the line is short .
I didn't touch the focus control or Astig it gos in and out of focus depending on the temp brightness control ...
Lest i can go out to day without wondering very happy with the results so far must be at least 60 or 70 years for this thing to finally light up unless they did a factory test .
Thanks Steve again for the help here
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Last edited by Harry Dalek on Sun May 28, 2017 11:02 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: The Tasmanian Devil VCR139....A for Andrew

Postby Harry Dalek » Sun May 28, 2017 10:59 am

Klaas Robers wrote:Harry, have you in your experiments conneted the deflection plates to any voltage? I would connect them to about the highest positive voltage. If not they can be charged by negative electrons and that will any way affect the result on the screen.

Steve, what would you do in this case?


Yes i did yesterday but just AC but today i used Steve's advice doing this and with the circuit changes it worked fine ...

I think i will do the deflection amplifiers next some time during this week i think i will have to ask Steve what are the miner resistor changes so i don't have to do it twice ..
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: The Tasmanian Devil VCR139....A for Andrew

Postby Steve Anderson » Sun May 28, 2017 11:21 am

Harry, I'll have a look at the deflection amps today, as I mentioned it should be just two resistors that need increasing in value in each amp.

The rest of the low-voltage circuitry should be fine as is, a simple copy of those for the 3BP1.

Klaas, the 'AC on plates' test I mentioned somewhere above fulfill the DC requirements as you mention. It's amazing how many people think you can leave the deflection plates disconnected and still get a good focused spot, many times you'll get nothing.

Steve A.
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Re: The Tasmanian Devil VCR139....A for Andrew

Postby Harry Dalek » Sun May 28, 2017 12:36 pm

Steve Anderson wrote:Harry, I'll have a look at the deflection amps today, as I mentioned it should be just two resistors that need increasing in value in each amp.


Thanks Steve much better than trial and error i'd have to do yes thats a very minor change !

The rest of the low-voltage circuitry should be fine as is, a simple copy of those for the 3BP1.

Easy pessy ! i should have all the parts so that will go quick next chance i have to do some building . i checked both astig and focus controls focus on the video and start up almost ..
Focus seems still a touch large i recall i think DOM and Steve O mentioning using the same tube having fine focus problems .
I ended up rotating the tube a touch it was a bit off as you saw .

Steve A.[/quote]

youtu.be/MXSsNB8Hfpw

youtu.be/jEYOP1H75c0
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Rotated the tube a touch was a bit of angle
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Re: The Tasmanian Devil VCR139....A for Andrew

Postby Andrew Davie » Sun May 28, 2017 12:50 pm

Fantastic!
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Re: The Tasmanian Devil VCR139....A for Andrew

Postby Steve Anderson » Sun May 28, 2017 12:50 pm

I've had a look at the deflection amps and I suggest building them exactly as before, no changes. I had forgotten that in the ramp/sweep generators we have R708 and R728 for exactly the function of setting deflection amplitudes. For the time being copy what you did before and if the traces are too large on the screen those two resistors can be adjusted, not four. Easy to do if they're mounted on the panel-pots at first, when the correct value is found they can be moved to the board(s).

Steve A.

For the moment the Astig control will have little effect, if any, that will improve once the deflection amps, sweep generators and the rest is built, tested and connected.
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Re: The Tasmanian Devil VCR139....A for Andrew

Postby Harry Dalek » Sun May 28, 2017 8:04 pm

Andrew Davie wrote:Fantastic!


Thanks Andrew in time i hope this little Tasmanian CRT will display a Raster what it can do depends on focus spot size it would be fine for 32 line at the moment but i would like to try for the higher this time .

Steve Anderson wrote:I've had a look at the deflection amps and I suggest building them exactly as before, no changes. I had forgotten that in the ramp/sweep generators we have R708 and R728 for exactly the function of setting deflection amplitudes. For the time being copy what you did before and if the traces are too large on the screen those two resistors can be adjusted, not four. Easy to do if they're mounted on the panel-pots at first, when the correct value is found they can be moved to the board(s).


Yes i have forgotten what i used if used them at all for the 32 line monitor but i do recall to use them if needed really easy then a dead copy ,Yes i will work on the deflection amps next ,get the parts together and copy when i get a chance .

Steve A.

For the moment the Astig control will have little effect, if any, that will improve once the deflection amps, sweep generators and the rest is built, tested and connected.
[/quote]

Its slight but i can see the control is doing some thing to the little line i have at the moment
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Re: The Tasmanian Devil VCR139....A for Andrew

Postby Harry Dalek » Tue May 30, 2017 7:46 pm

Bit of spare time more construction i have finished the deflection circuits apart from the same mistake i made last time :roll: i will fix that up tomorrow either removing copper matrix connections around this area or just copying Steves idea to reduce capacitance in this area .
Something that comes to mind around this Stage on Troy's 3bp1 monitor he was trying balance hes deflection amps he was getting movement of the raster dot fine center to one side and partly to the other , i was looking at getting Troy to adjust the resistance on the 180k resistor at the collector on the side giving problems and balance them that way , Troy had the idea to try the 1.8k resistance on Emitter and that worked he had to increase it to 3.3k i think he ended up replacing both to this value .
I am working with Trimmers at the moment i will see what i might change to pots later on ...easier quicker build this way .
Also the placement of the deflection circuit means wiring to the deflection plates will be short better than i did on the 3bp1
See how i go when i test perhaps tomorrow .
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Re: The Tasmanian Devil VCR139....A for Andrew

Postby Steve Anderson » Tue May 30, 2017 8:21 pm

Harry, I'm not quite sure I understand what you are saying above, nor what problems Troy had. I wasn't aware of the problems at the time, either that or I missed them. The amps should work as advertised. If it's a case of too much gain in the deflection amps adjusting the differential pair emitter resistors equally is correct, but you can only take this so far.

If you can provide a sketch or even just a listing of what values you both ended up with that would help me understand what's going on, e.g....

R404 = 3K3
R405 = 3K3...and so on...and any other changes you both may have made...I only need the changes you both made to the circuit above.

This sort of feedback helps, remember I haven't built these amps (but they have been simulated) or ever used the two tubes you are using. So your input is valuable. I don't want others, or even myself, to have to go through the same process.

Steve A.
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Re: The Tasmanian Devil VCR139....A for Andrew

Postby Harry Dalek » Tue May 30, 2017 9:36 pm

Steve Anderson wrote:Harry, I'm not quite sure I understand what you are saying above, nor what problems Troy had. I wasn't aware of the problems at the time, either that or I missed them. The amps should work as advertised. If it's a case of too much gain in the deflection amps adjusting the differential pair emitter resistors equally is correct, but you can only take this so far.


Steve Troy pretty much made the circuit to design but i think as i recall the collector 180k resistors were a bit off he was using what he had handy on those resistors,he was showing me results and i saw they were out of balance so the resistance's on the collectors were a touch off ,Troy tried the emitter resistors which seemed have the same result Troy was happy with that and he just went on with the rest of the project ,i just thought i would mention it as had me wondering since that worked also .

If you can provide a sketch or even just a listing of what values you both ended up with that would help me understand what's going on, e.g....


I don't recall what hes 1 watt resistors were i think they were closer to 170k pretty sure they were lower than 180k

R404 = 3K3
R405 = 3K3...and so on...and any other changes you both may have made...I only need the changes you both made to the circuit above.


Yes pretty much those were the changes only changes as i recall ....i was at the time thinking more to change balance the 1 watt resistors up but hes idea seemed to work /

This sort of feedback helps, remember I haven't built these amps (but they have been simulated) or ever used the two tubes you are using. So your input is valuable. I don't want others, or even myself, to have to go through the same process.

Steve A.
[/quote]

Yes i understand i was interested at the time and at the time it wasn't my build so i left it at that but i was very interested that r404 and r405 change worked ...well the circuits for this are getting a number 3 go so i don.t think it needs a 3 times lucky we know it works well /
only thing on the build i am not sure about is will it handle the sync i want 60 line thats ok still 12.5 hz side 750 hz ? but 120 line thats double 25hz and 3000 hz ,
and it will be horizontal scan this time .
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Re: The Tasmanian Devil VCR139....A for Andrew

Postby Steve Anderson » Wed May 31, 2017 11:27 am

Thanks Harry. I'm surprised that you both had to 'fiddle around' with resistor values. I know you tend to recycle components, it may be worth measuring the collector and emitter resistors before soldering them in place. The exact value isn't so important but a reasonable match between them, within a few percent, would be preferable. You only have to select a pair per amp, not all four. 2x180k and 2x1K8 per amp. With new components this shouldn't be needed, even with 5% resistors, when new they're usually somewhat better than 5%.

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Re: The Tasmanian Devil VCR139....A for Andrew

Postby Harry Dalek » Wed May 31, 2017 1:58 pm

Steve Anderson wrote:Thanks Harry. I'm surprised that you both had to 'fiddle around' with resistor values. I know you tend to recycle components, it may be worth measuring the collector and emitter resistors before soldering them in place. The exact value isn't so important but a reasonable match between them, within a few percent, would be preferable. You only have to select a pair per amp, not all four. 2x180k and 2x1K8 per amp. With new components this shouldn't be needed, even with 5% resistors, when new they're usually somewhat better than 5%.

Steve A.


Hi Steve

Troy wanted to use what he had handy so there was a bit of matching i do recall they were not 180k for the 1 watt collector resistors but as i said lower ...Testing he was having a bit of trouble around this area but he managed to even the deflection sides up .He wanted to use what he had and i can understand that everything said he got it going !

Steve next post here i have tested my deflection amplifier i reviewed the procedure you kindly helped me with last build and was a bit easier this time around apart from my meters only one will do the current reading across the 0v and Tr403 and 503 collectors had me head scratching swapped to a different brand meter and it was fine ...so take note any one out there meters can be fickle !
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: The Tasmanian Devil VCR139....A for Andrew

Postby Harry Dalek » Wed May 31, 2017 2:12 pm

OK i am happy to report my deflection amplifiers seem to work doing a procedure test ...
BTW the 1 watt resistors on mine are closer to 178 179k i had to mix and match as well what i had handy ..
Re: 3BP1

by Steve Anderson » Wed Dec 16, 2015 5:30 pm
Testing time, no need for the CRT or the -ve 1.5kV, this can be done in isolation on the bench.

With VR401 at the R401 end of the track and VR402 at the 0V end, connect a current meter between TR403 collector and 0V/GND, apply -12V only and adjust VR403 for 2.0mA indicated. Switch off and disconnect meter.

Then connect the +360V supply and the -12V supply (no need for the +12V yet). The collector voltages of TR401/402 should be roughly equal at around 180V. If they differ by say 20V don't worry.

Update. In fact it would be useful to know what those two static voltages are.

If that is the case power down and add the +12V to R406. With VR402 still at the OV end of the track all should be just as before.

Gradually turn VR402 towards R406, the collector voltage of TR402 should drop, as it does so the collector voltage of TR401 should rise an equal amount but in the opposite direction.

If all is well so far the amplifier is working. Build up the '500' section (horizontal) and repeat the testing for that channel. If all is well disconnect and put aside. Now we need to get on with the sync separation and ramp generation. Do not be tempted to connect to the CRT yet! In fact disconnect the heater of the CRT now until all voltages and waveforms appear sensible. The CRT is the one thing that you will find difficult to replace, don't risk being impatient!

Steve A.

[color=#0000FF]I repeat...Set VR402/502 to the 0V end, measure and note each collector voltage. Adjust VR402/502 such that TR402/502's voltage decreases by 20V, you should find that TR401/501's collector voltage has gone up by 20V - i.e. an equal amount.

So what I'm looking for is something like this...

VR402 at 0V
TR401=145V
TR402=155V
...then
TR401=165V
TR402=135V
[/color]
So looking at the readings and adjustments there Steve i would say i have working deflection amplifiers ....i suppose next step are the sawtooth generators i am thinking the 12.5 hz is known value the 60 line on the horizontal has to run at 750 hz and 120 line if i go with 25hz 3000 hz ...these 2 easier theres Gary's software to input video above this its onto a flying spot scanner .
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