5AHP7A Vintage SSTV The Deep image

[Klaas Robers]

Harry, Steve, I can make a pdf of the word file in which the circuit diagrams are. However it is very old electronics. For the sawtooth oscillators I used a unijunction transistor. I fear that these are nowadays no more available.
But in which way can I transfer the pdf best to you? Include it in a post?

The resistances of the coils look promising. Higher than mine. And because you have + and - 12 volt while I have just + and - 6 volt, that will fit I think.

The magnetic deflection has the advantage that you may put the cathode and the grid of the picture tube at a reasonable positive voltage, somewhere between 0 and 100 volt. No need for isolation towards the grid or cathode video modulation. That is a big advantage of magnetic deflection. Only + 5 to 7 kV as an accellerator voltage.

hm.... let me try to include the pdf...... Captions and titles in Dutch. Not too difficult to decypher.

You will see the size of my PCB's. And yes, I had the advantage of access to the Philips potcores, so I could make inductances at will. I like passive filters.

[Harry Dalek]

Harry, Steve, I can make a pdf of the word file in which the circuit diagrams are. However it is very old electronics. For the sawtooth oscillators I used a unijunction transistor. I fear that these are nowadays no more available.
But in which way can I transfer the pdf best to you? Include it in a post?

Thanks Klass for posting your monitor schematic ! some of the ics the limiter IC i remember not sure thats about any more ,i got a unijunction transistor a year or two back so a sstv voltage controlled oscillator circuit i saw in the sstv hand book it worked so they are still about ..
Did you ever get it published ? looks very compact and still looks advanced to me !

The resistances of the coils look promising. Higher than mine. And because you have + and - 12 volt while I have just + and - 6 volt, that will fit I think.

Yes i was not expecting the results least that makes it a bit easier .

The magnetic deflection has the advantage that you may put the cathode and the grid of the picture tube at a reasonable positive voltage, somewhere between 0 and 100 volt. No need for isolation towards the grid or cathode video modulation. That is a big advantage of magnetic deflection. Only + 5 to 7 kV as an accellerator voltage.

All the monitor circuits i have seen use the one transistor and high voltage supply and modulation to the cathode and a few to the control grid again i am a ways off till i see how this go's,

hm.... let me try to include the pdf...... Captions and titles in Dutch. Not too difficult to decypher.

That worked fine Electronics is Dutch is no problem on most of it i could see what the boards were,

You will see the size of my PCB's. And yes, I had the advantage of access to the Philips potcores, so I could make inductances at will. I like passive filters.

[/quote]

I still have my old 88mH ones it was the thing to do back then ,for me i like them apart from they are big and use up a lot more room pcb than a opamp,

[Harry Dalek]

...I am very aware of the bad memory problem...I probably forgot you had built up some of the circuits for this.

If what you've got already is working as it should I would leave it, no point in re-working it all. If you spot errors or something refuses to cooperate let us know...

Steve A.

All the schematics in that CQ magazine TV are made apart from its power supply i went a different direction, all i did was here use Ralph's 300 volt dual supply and a pretty standard dual 12 volt supply circuit ...i can see the mistake in the negative dual supply in the cq version how they didn't pick that up i don't know then again i didn't see it till you mentioned it,

The first large circuit in the schematic pretty much is ok i think i have to re look at the Monostable's i don't remember i if i tested those.

i appreciate you looked at the sync detector circuit it was the first thing that was giving my problems and i did get it going but i would like to see how close i was to your solution ...i know the main problem was around those 2 pots main control is on board mounted for now ,,,,,

It says in the pdf the sync filter has a 100 hz bandwidth where it was always a 400 hz bandwidth in other monitors for poor signal,,,, but 80hz no where near around the filters center frequency no wonder it didn't work ! this is very useful having your correct fix i will look at my circuit today see what i did ....Now i know what was up !

Does make me wonder what else went wrong from the original working to the schematic copy ,the good thing is these things are easy to change and tack on another idea if need be ,doesn't work make it work another way .

[Steve Anderson]

All printed material suffers errors from time to time, some are better at catching them before the presses start rolling, some not. In the case of circuit diagrams, often these were sub-contracted out to companies who did all sorts of drawings, mechanical, architectural, flow-charts and - circuit diagrams. For most magazines it was too costly to employ full-time staff to do this who wouldn't have that much to do usually.

You can't expect the draftsman to be conversant in all disciplines so it should go back to the author for proof-reading. How diligently the author checks the work is one thing, both text and diagrams...if he even gets the chance to proof-read it or even can be bothered.

Often the author can get 'too close' to his work, it's so familiar the errors that are glaring to others are missed. Bad hand-writing and scrappy 'fag-packet' sketches don't make the draftsman's or typesetter's work any easier.

Text can be proof-read by most, but the technical aspect, especially diagrams, requires those with knowledge and experience, often they're also too expensive so this stage is omitted...and there they sit, waiting to catch you out, errors lurking in the details.

Steve A.

[Steve Anderson]

Going back to that filter, once the errors are corrected it works as advertised. It does centre on 1200Hz and its bandwidth is about 120Hz with a gain of 1.0.

The problem of the 50 Ohm pot could be fixed by raising its value and adjusting all the other values in that stage to suit, but if you've built it already, leave it be...apart from correcting the errors.

Steve A.

[Harry Dalek]

Going back to that filter, once the errors are corrected it works as advertised. It does centre on 1200Hz and its bandwidth is about 120Hz with a gain of 1.0.

The problem of the 50 Ohm pot could be fixed by raising its value and adjusting all the other values in that stage to suit, but if you've built it already, leave it be...apart from correcting the errors.

Steve A.

I suppose it happens So often and worse these days on the net with wiring mistakes ...OH well...onto my mistake

Looking at what i did drawing it down ....on the filter posted below i think its more bypassing the filter if any thing with the pots i now recall it just would not work ...So i will use your corrected circuit and see when i get up to this stage and see ..

I now have hard wired the Ac socket to the monitor and tested with the AC power supply and DC HV Low Voltages ,so the 3bp1 cable will work on both monitors this way every thing is standard .

[Steve Anderson]

Oh well, sadly there's no chance of that modified filter doing anything much. So when you can change it to yesterday's sketch and see if you get nice fat bursts if 1.2kHz coming out of it. The sync frequency in my posted SSTV wave files is quite close to 1200Hz so it should pick them out easily. It will need tuning via the pots first using those files...

Steve A.

[Harry Dalek]

Oh well, sadly there's no chance of that modified filter doing anything much. So when you can change it to yesterday's sketch and see if you get nice fat bursts if 1.2kHz coming out of it. The sync frequency in my posted SSTV wave files is quite close to 1200Hz so it should pick them out easily. It will need tuning via the pots first using those files...

Steve A.

My sync indicator blinks away nicely but i suppose that along with every thing else going on there ,so grateful for the interest there looking at it .

Yes thats good i can use you video files for testing and will use your sstv reversing wav as its worth using here as well,now i have its power supply i can hook it up and see how the circuits go .

If i have time tomorrow i will hook stuff up and look on the scope see where the problems are .

[Klaas Robers]

The TAA350 is an old TV sound-IF (5,5 MHz) limiting amplifier. It has an amplification of 80 dB and limits nicely symetrically. The FCH (gates) and FCK (one shot) are Philips DTL circuits (Diode-Transistor-Logic). This logic family lost the battle against the TTL circuits. They are for a long time no more available, however I have saved quite a lot of them.

In my monitor the limited input signal is used for extracting the sync, but also this runs to an output amplifier (print 13), where it is low pass filtered and amplified to 0 dB line output level. The low pass filter is made of simple micro chokes. This signal is especially for recording. Of course it follows the source selection switch, so if I connect a recorder, it records the signal that is displayed on the monitor, wherever it comes from.

The selective output muting (print 14) is because it is of no use to record if the same recorder is selected as the input. The same applies to the connection to the short wave transmitter/receiver. You can't transmit the audio that comes from the receiver at the same time. So when the receiver (RCVR) is selected as the source, there is no signal available for the transmitter input.

[Harry Dalek]

Hi Klaas
I think i have a very tarnished and pitted round can TAA ic i think might be the same ,no idea where i got it from ,thats still a very good monitor and very small in in number of circuits as well in boards .

I can see it used some very clever ideas not used in other monitors .,

I think you would of made some use of of in the 1970s ! If you ever track down the old recordings i am sure steve and I would be keen viewers of the past classic Slow scan .

[Harry Dalek]

I have been reviewing the the QST dec 75 monitor circuit and its mentioned the monitor circuits were in part copied from George R Steber Slow scan to fast scan tv converter QST magazine .

March SSTV to Fact-Scan Converter, Part I p. 33
(Steber) 8 pages

May Slow-Scan to Fast-Scan Converter, p. 28
Part II 10 pages
(Steber)

Any one have these issues ? i should look in the hand book some times stuff like this is reprinted the schematics any way .

Page 86 of this pdf has a little bit on sstv

[Harry Dalek]

I had a go at tackling Steve's reworked sync filter ,Steve i ended up using 22nf for the 2 caps for now till i find some 27nf, i tried some down to 1nf and some other values just to see the results in filtering out the video frequency ,not perfect but the sync is above any low frequency dark video that is that end of the spectrum ,seems similar to the bottom of page scope result picture but not as perfect as that lets hope since its a drawing there's some artistic reworking there

So the resistor to the filter is back to a 56k and your filter worked right off more than i can say happened in the magazine version .

I then had a look at the low pass filter thats fine ...all of board one so far seems ok moved onto 2 second board with the 74123 monostable's and the 555 horz vert deflection oscillators the vertical i am not sure about i see it needs a manual reset switch i have not put in yet horizontal looks ok .

Thats about as far as i got today .

[Steve Anderson]

I had a go at tackling Steve's reworked sync filter..

Well it's not really re-worked, just re-drawn as it should have been, I claim no originality for it. I'm sure the original worked as it should have, it was simply the sloppy translation from fag-packet sketch to printed article that caused you headaches.

The filter values can be adjusted widely to achieve the same result. I had a look around a few days ago and it seems the lowest value front-panel pot that is easy to get is 1k, 20x the original 50 Ohm version. But if you raised all the other resistors in this filter by the same factor and reduced the capacitor values by the same amount you'll end up with the same result.

BUT, the 82k resistor becomes 1.6M and you could not use a 741, something like a TL071 as a minimum would be required.

In fact, for the heck of it I recalculated the values which are a bit different to exactly x20 but end up being a better filter. I simulated it with a TL071 and the curves are below. The red trace is the frequency pot in the centre, the other two are with the pot at either end.

Because some of the values are now quite high you'd need to be careful with hum pick-up.

Steve A.

[Harry Dalek]

I had a go at tackling Steve's reworked sync filter..

Well it's not really re-worked, just re-drawn as it should have been, I claim no originality for it. I'm sure the original worked as it should have, it was simply the sloppy translation from fag-packet sketch to printed article that caused you headaches.

Well i am Glad you had a look at it ,i tend to blame my self more than thinking the published circuit is wrong ,i don't have an eye for mistakes like this one !

The filter values can be adjusted widely to achieve the same result. I had a look around a few days ago and it seems the lowest value front-panel pot that is easy to get is 1k, 20x the original 50 Ohm version. But if you raised all the other resistors in this filter by the same factor and reduced the capacitor values by the same amount you'll end up with the same result.

I noticed the different setting range on the trimmers as i changed the filter capacitors 1nf was just in range but very tight,i didn't go higher than what i had already ,just have the 2 22nf in at the moment .a 1k pot would be better.

BUT, the 82k resistor becomes 1.6M and you could not use a 741, something like a TL071 as a minimum would be required.

I think have 71 and 81s might be worth a try and see ...theres a job for me when i can get back out to the shed .

In fact, for the heck of it I recalculated the values which are a bit different to exactly x20 but end up being a better filter. I simulated it with a TL071 and the curves are below. The red trace is the frequency pot in the centre, the other two are with the pot at either end.

Because some of the values are now quite high you'd need to be careful with hum pick-up.

Steve A.

Well i like the idea of it and that looks good ,sort of an easy change to when i am off work later in the week i will try it for sure ..better filter sound good to me .

[Harry Dalek]

I still need to try your filter upgrade Steve i found a Tlo71 didn't have time to day to change the parts needed for it but wacked it in just to see ,i had no indicator via the led but on the scope even with the parts as is it looked a lot cleaner .

I will do this correctly in the next day or 2 .

For now i put back the 741 in the sync filter circuit and checked output of pin 12 of the 7404 and a nice clean pulse with no rubbish even with the sync filter as is ..........next looked in to whats coming out of the 74123 ic side A and nothing checked the input in case it was not wired up but its at the input of pin 2 checked the power supply on the pins all correct checked the wiring all correct and swapped the ic same result ..i will look for any solder bridges that may be there ,circuit looks ok to me ....if i get passed this ic i can check the rest so far i know nearly half is working .
Power supply works
Limiter works
sync filter works
sync pulse filer works
Low pass filter works

Edit i think we have a problem another circuit mistake i have just noticed the 22k resistor is connected to pin 14 of the 74123 where as it should be 15 arrrrrrrrrrr
Love to know the feed back to CQ magazine after 3 circuit mistakes so far and i think a 4th on one of the 555 oscillators we will see when i get around to it .