The Tasmanian Devil VCR139....A for Andrew

[Harry Dalek]

In general you should be able to adapt all of the 3BP1 circuits to the VCR139A, it's much the same as any CRT from that era. You just need to adjust some voltages here and there, I'm confident you can do that, but if you get stuck...well, you know where others and I are...

Thanks Steve thats good that makes it much easier i have a good idea what to do now and how most it still went and what not to do ...this time i will have it well grounded for a start .

I am more confident Steve on this one apart from changes on how well it will work but most of it should go a lot easier than last time.

Yes, the opto-isolator should be good for up to a few hundred kHz, beyond that, say 405/525/625, a faster device would be required. Though on a 3" screen it's doubtful if you would see any difference. !20/128 lines (SSTV) is about the limit on a 3" screen. Even at 72 lines as I did a few years back, the lines are starting to merge with each other.

Steve A.

Much better to go with this design i have a few of the same opto couplers...
I was thinking the thing will have to be well focused for the higher line rates yes i can see these small tubes have there limits even so useful to learn and i want one is my excuse

[Steve Anderson]

I was thinking the thing will have to be well focused for the higher line rates yes i can see these small tubes have there limits even so useful to learn and i want one is my excuse

The limit is basically the spot size when well focused. With these type of tubes it's around the 0.3-0.7mm size when operated at their near maximum ratings. At lower voltages the spot will be larger and not so bright. This can be a problem in raster-type displays. But one never knows until you try it. Good luck.

I'll keep looking 'over your shoulder' to see how you're getting on, but I'm confident you can do this on your own. I don't mean to sound condescending at all. You've got more experience than many with CRTs.

Recall the sparks or something you had with the opto-isolators...that was a lesson for both of us....

Steve A.

[Harry Dalek]

The limit is basically the spot size when well focused. With these type of tubes it's around the 0.3-0.7mm size when operated at their near maximum ratings. At lower voltages the spot will be larger and not so bright. This can be a problem in raster-type displays. But one never knows until you try it. Good luck.

I'll keep looking 'over your shoulder' to see how you're getting on, but I'm confident you can do this on your own. I don't mean to sound condescending at all. You've got more experience than many with CRTs.

Recall the sparks or something you had with the opto-isolators...that was a lesson for both of us....

Steve A.

Hi Steve
No worries i am trying to be careful here the power supply is very important and trying to get this right .
Working on the positive side today looking at it logically voltage could not be more than the 3bp1 which is a higher voltage tube and i am getting 386 volts with a 68k load this dropped to 370 volts ...should be more than enough for the deflection amps and such .
Yes as i mentioned i made sure this time i had earthed the power supply lost 2 sets of ics last time ..it was something i also mentioned to Troy to make sure he didn't make my mistakes on he's build and a few other tips ...i suppose you get better at the CRTS as you make the next well fingers crossed !
Yes also just yell out if i am heading down the wrong road rather not stuff it up !

[Steve Anderson]

...also just yell out if i am heading down the wrong road rather not stuff it up !

That I will Harry.

Steve A.

[Harry Dalek]

That I will Harry.

Steve A.

I will try to do good !

I pretty much finished all the power supply high and low unless it looks wrong seems to run ok
No Bangs smells overheating thank goodness .
I pretty much used junk box parts and a few ebay buys i had left from last year .
I forgot to mention the high voltage supply readings are with load resistors 68k for the positive and 200k for the negative.

I will work on the CRT circuits i think next ...

I was wondering since its not good to run the tube without deflection if i supply a AC supply 30 100 volts to say the horizontal deflection plates would this be safe just as a test before the deflection amplifiers are constructed i am thinking yes ?

[Steve Anderson]

Yes, it's good to put something AC on the deflection plates when you fire it up rather than nothing. A stationary spot can easily produce a burn if something isn't right in the grid/cathode circuit. it can simply be a few dozen volts from a transformer to keep the spot moving until you're happy with the brightness/focus and astigmatism (where used) controls.

Steve A.

[Harry Dalek]

Yes, it's good to put something AC on the deflection plates when you fire it up rather than nothing. A stationary spot can easily produce a burn if something isn't right in the grid/cathode circuit. it can simply be a few dozen volts from a transformer to keep the spot moving until you're happy with the brightness/focus and astigmatism (where used) controls.

Steve A.

Today i had time got the parts together and copied the 3BP1 CRT circuit and even had enough time to test the voltages and give it a test run ....
Unfortunately not a trace of a trace
Voltages seemed what would be expected but now i have run out of time to double check for any mistakes .
Across the 75 volt Zener is 72 volts thats fine testing across the 5 volt one i am getting a range of 04 to 6.2 volts when i adjust the brightness control of the opto coupler so the opto must be working this Zener diode must be a 1N4735A not a 33A .
I did try the test with 15 volts ac across the deflection plates Steve ,even turning the power off some times you can see a trace of green with the voltages fading away if some voltages are not right on full on but no hint at all yet ...
I know all CRT's need tweaking if i have made no mistakes i will sure have to do this ..the low voltage Zener is one thing i need to look at .
Well good thing again no bangs smoke and voltage behaved !

[Andrew Davie]

Watching with interest. If it doesn't live, then I have another tiny tube I can send you to play with.
Cheers
A

[Harry Dalek]

Watching with interest. If it doesn't live, then I have another tiny tube I can send you to play with.
Cheers
A

HI Andrew if the tubes heater didn't light up i would be worried and also if i saw white coating in side the glass it looks fine i can't blame the cathode ray tube ....i have to blame my self so far i have not had a chance to double check every thing ..no bangs or heating in the circuits so can not be bad ..i am just about to double check the pin connections to the crt to other data ..i used one without checking it to others so i will see at least if the voltages are going to the right pins .
...Might not have time tomorrow to check more which is a pain but i will get to it .
If I have it in me Andrew this thing will display some thing not given up yet only started
Think my tube connections are ok looking picture shows what i used unmarked pins are the deflection plates

[Steve Anderson]

If you're getting a short flash of green when you turn off the power this is good news and means the applied voltages to the CRT aren't quite correct and that the tube is probably intact.

I'll do a comparison between the two different tubes and see if I can come up with any suggestions. I'll need to find the 3BP1 circuits first, I certainly have then, but in what folder did I put them? Some of my folder names are a bit cryptic and defy me at times...

Steve A.

Ah! Found 'em...in a folder called 'Harry'. Not quite so cryptic after all.

[Harry Dalek]

If you're getting a short flash of green when you turn off the power this is good news and means the applied voltages to the CRT aren't quite correct and that the tube is probably intact.

I'll do a comparison between the two different tubes and see if I can come up with any suggestions. I'll need to find the 3BP1 circuits first, I certainly have then, but in what folder did I put them? Some of my folder names are a bit cryptic and defy me at times...

Steve A.

Ah! Found 'em...in a folder called 'Harry'. Not quite so cryptic after all.

HI Steve no no hint of green light at all i was looking for that !

Different in that A1 is connected to A3 i really don't have that much experience with different electrostatic tubes to know the difference between them i will when i do end up seeing a green trace with the arrrr moment but not sure yet and again i must blame me for now ...
I must do a Steve folder ! mine was 2016nbtv monitor
Looking at my readings the 75 volt zener is showing 72 volts a touch lower ...perhaps because voltage is a lot lower ?mmm
The readings around the focus part of the circuit + 202 -470 and bottom of focus pot -408 ....power supply voltages look about the same i didn't write those down to the volt .

[Steve Anderson]

I wouldn't apply volts again until I get to the bottom of this. Different companies often refer to various anodes in different manners, easily leads to confusion.

As for the 'green flash', I must have misread your posting.

Steve A.

[Harry Dalek]

I wouldn't apply volts again until I get to the bottom of this. Different companies often refer to various anodes in different manners, easily leads to confusion.

As for the 'green flash', I must have misread your posting.

Steve A.

Yes no light from the tube yet ...like the The Rolling Stones - (I Can't Get No) Satisfaction till i see that green light !

OK i will wait and see what you think about this ...there was no sparking or any thing ..when i can power up again i will check voltages at the tube pin connections ,

[Steve Anderson]

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.

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.

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.

[Steve Anderson]

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.