5AHP7A Vintage SSTV The Deep image

[Harry Dalek]

Oei Harry, I never work in that way. I always build stage by stage and first checking the just built stage. Then I always have a working circuit, or the fault is in the last built stage. Even when I rebuilt the old working monitor on a wooden frame onto the aluminium frame of the Heathkit SB500, I assembled and tested it small PCB by small PCB.

OH i agree Klass thats the way to go for sure ,i made my first SSTV monitor that way .

It is extremely difficult to find faults in the large circuits that you have built. At least for me..... Good luck. You'll need it.

I have PMed the the circuit to you to have a look at ,only reason i made it this way was it was from CQ magazine i would think it would of been checked before being published ,even so i expect it will need looking at here and there with changes which is always the way ,not all parts are 100% the same ...mistakes odd bad soldering connections;
i will take your good luck for sure

For the 5 kV, I think that you can use the small module. However, you should make a voltage stabilization for it. That is the input voltage should be dependent of the output voltage.

Oh so it really needs feed back to be stable its a lot of voltage to drop

Do you have the ability to measure high voltages to say 10 kV?

Yes i made a HV probe for when Steve was helping me with power supply the 3BP1 yes it will do 10 kv fine .

The first thing then is to connect the module to a variable input voltage and measure the output voltage. Find the input voltage that gives you 5 kV of output voltage. For my self built fly back inverter with voltage multiplication this was about 14 volt. Two very high ohmic and long resistors in series bring this high voltage to an opamp circuit that regulate the input voltage of the inverter circuit by feed back. This circuit is fed from a voltage of about 24 volt. Then the 5 kV becomes a stable 5 kV, which is what you need.

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Well this is some thing i have never tried and the module does only run up to 3 volts ,very high ohmic resistors might be a problem to find ,i might have to do what i can with what i have got ...if the feed back resistance can be over come and get the voltage down to some thing perhaps also a 4046 as a vco could be used ..might have to be low tech for the start i will have a think about it.

[Harry Dalek]

I wasn't going to use the outer case as it was a little beat up and had a gap on the front panel ,think this case was used for some timing electronics to add chemicals to a swimming pool so very odd front panel gap

Sort of like the idea to use it at the end like this ,used a Large power supply fan case as a short hood just the right size then i had an old TV speaker grill i was going to use for an outer case for something once i bent it to size but liked the logo still on it cut the mesh out and bent it to size ,it covers the hole gap nicely .

Renamed this project with the Deep image logo.

[Harry Dalek]

Had time to have a good look at the first board today used one of Steves sstv 8 level reversing bar videos for the test .

I have a little problem around the 1200hz filter but changed the circuit a bit seem to be getting same wanted results .

This is around the area of the circuit shown in the first 3 images ani gifs below around the sync indicator led .

Moved on to the low pass filter for the video this seems to work as well bit hard to film or take a picture the stair case of the revering bars are much easier to view live on a analog scope best i could do here was show one at time SSTV waveforms are harder to record an image or video than NBTV .

i will hook it up to the next board which has some monostabes a horizontal noise rejection idea see what results i get there .

I should of posted the last picture first as thats the limiter i am using ,the circuit used a 709 which i didn't have so used this limiter instead same as for my glow drum mechanical monitor .

[Harry Dalek]

Today i tested the CRT heater as in seeing it light up which was reassuring !

Worked on the panel control arrangement and get that out of the way so i can leave the CRT in the case got most of it done might have to add another switch .

Arrr were not expecting that viewing port at the top mmm! came with the case

[Harry Dalek]

MY thoughts return to my SSTV project time to start working on this some more .
Today i put in a bracket to keep the CRT safely in place and the power supply plug socket ,i will use the same AC power supply as the 3BP1 for same reasons ,since i will be using the same plug socket system i will have to make sure i keep the cable standard to both in case they get swapped one day or at least mark the cable so i know whats what .
The hardware part is over one of those things needed to be done ,i will start on the power supply ,as in feeding it to the case and working on the dc supply for the circuits .
I will keep in mind the things Steve had taught me on CRT safety and test once i have deflection via the yoke ....this tube is rare in my neck of the woods !

[Steve Anderson]

Harry, I uploaded a batch of SSTV wave files some time back, if you haven't downloaded them they're still there...scroll up/down for more...

viewtopic.php?f=8&t=1926&start=270

I'm not sure, but I will check, they're probably 120-line EU standard, if you want 128-line and/or US standard just let me know and I'll knock up a few.

Steve A.

[Harry Dalek]

Harry, I uploaded a batch of SSTV wave files some time back, if you haven't downloaded them they're still there...scroll up/down for more...

viewtopic.php?f=8&t=1926&start=270

I'm not sure, but I will check, they're probably 120-line EU standard, if you want 128-line and/or US standard just let me know and I'll knock up a few.

Steve A.

I am just working on the high voltage power supply ,if the circuits i made before workout it should be able to do both ,but its still aways off being finished .
I will check the wav files for sure .

[Steve Anderson]

True, at this stage it really doesn't matter what format the signal is in. Indeed, there is no reason why the finished article couldn't handle all four combinations of line-quantity and line-rate. They are all quite close together, all that would be needed is a slight twiddle of the 'size' pots.

Steve A.

The uploaded wave files I mentioned earlier today are 120-line EU standard, 16.7Hz line-rate.

Also the 'A' version of the CRT you're using, 5AHP7A, "The type 5AHP-A utilizes an aluminized screen for greater light output and to minimize screen charging effects...". (Not my spelling, from the Du Mont datasheet).

[Harry Dalek]

True, at this stage it really doesn't matter what format the signal is in. Indeed, there is no reason why the finished article couldn't handle all four combinations of line-quantity and line-rate. They are all quite close together, all that would be needed is a slight twiddle of the 'size' pots.

Steve A.

The uploaded wave files I mentioned earlier today are 120-line EU standard, 16.7Hz line-rate.

Also the 'A' version of the CRT you're using, 5AHP7A, "The type 5AHP-A utilizes an aluminized screen for greater light output and to minimize screen charging effects...". (Not my spelling, from the Du Mont datasheet).

Those SSTV wav pictures will come in handy on the testing stage for sure ! theres the odd this and that on the net people have put up of their old recordings but as you mentioned these least i know what they are for a start.

Yes i sort of lucked this version of the CRT for sure !

I was working on the power supply today ,i have an example of a 5AHP7 used in a SSTV in Ralph's june 1973 73 magazine version control grid modulated most of the others are cathode modulated using the 5fP7 i have seen ,the circuit i am going to use or try uses one of these so i will have to fiddle around here when i get to it /

The voltage results on the high voltage supply on the first set of caps are 380 380 volts DC so need to drop the focus control grid voltage some what looking at the normal operating range but both are within the maximum range ,rather drop that 80 volts than perhaps push the tube to much ,i see Ralph dropped perhaps 50 volts with the 1 meg resistor with the brightness control via the cathode .

Sort of trying to get it in the range of Ralphs HV power supply 300 volts looks good or a little closer to there sounds safer to me .

[Steve Anderson]

A basic HT of around 300V is going to be fine, anything from 300-350V at what is going to be a few mA, under 10mA probably. Two back-to-back transformers will be ample I would have thought. Use the intermediate windings for low-voltage purposes.

The greatest challenge in all this is the magnetic deflection. Here I have to say I have no experience with this, voltages are low, currents can be high. Ralph, Klaas and others will be your guide, not I. Though I do have a few thoughts on the matter they're totally untried. So over to those that know better...ditto the few kV you'll be needing!

Steve A.

[Harry Dalek]

A basic HT of around 300V is going to be fine, anything from 300-350V at what is going to be a few mA, under 10mA probably. Two back-to-back transformers will be ample I would have thought. Use the intermediate windings for low-voltage purposes.

The greatest challenge in all this is the magnetic deflection. Here I have to say I have no experience with this, voltages are low, currents can be high. Ralph, Klaas and others will be your guide, not I. Though I do have a few thoughts on the matter they're totally untried. So over to those that know better...ditto the few kV you'll be needing!

Steve A.

I am going to use the same Ac power supply as used for the 3BP1 unless this is a problem ,all i have to do swap the cable and plug it into this monitor case to supply the High and low AC voltages .

I tried dropping the DC from my circuit got a range from 290 to 360 ran out of time today with some other work to finish it ....do that tomorrow not to much of a problem .
I am using the load resistors to trickle the voltage away on switching off ....still have to be very careful ,i am using 220uf 400v caps on mine i had handy one shock from these beasts will not be good !

I made a 5fP7 SSTV monitor many years ago all worked well apart from the focus coil would get warm after some use and the raster would defocus a bit so i am not keen on focus coils .

Electrostatic focusing is more to my liking ! i suppose i see your point on the deflection side also but with this i had no choice have to take what you can get manged to do this a few times so see how this gos this time .

I hope i don't have to many problems at the moment plan is power supplies and deflection have that the rest should follow .am going to use or try one of the 7kv Power Modules i have worst case i will just make a EHT supply but hope the module works it will be small and neat .

[Harry Dalek]

Today i finished the High voltage supply getting positive and negative 315 and 320 Volts DC so something to work with now .

Tested the CRT Heater nice to know it still lights up /also looked into one of the 2 types of KV modules i have this ones the higher one runs up to 10KV running it on 5 volts i am getting a nice 6900 volts AC.

Still have to make the low voltage dual supply and one for the module .

Once i have that it will go a bit quicker .

[Steve Anderson]

...I am getting a nice 6900 volts AC.

Do you really mean AC or DC? You'll be needing DC as I'm sure you're aware.

If it is actually AC getting some rectifiers and a capacitor suitable might be a bit tricky.

Steve A.

[Harry Dalek]

...I am getting a nice 6900 volts AC.

Do you really mean AC or DC? You'll be needing DC as I'm sure you're aware.

If it is actually AC getting some rectifiers and a capacitor suitable might be a bit tricky.

Steve A.

HI Steve
Yes raw AC out of this like a old flyback ,i am not sure of the frequency used theres no data for the inside of these things given apart from voltage needed and output KV.
Yes also i need positive DC around the 7KV.
I have used Microwave rectifiers 20kv before this has worked with older fly back transformers that did not have a internal diode ,suppose i could also use 7 1kv diodes in series....... at times you have to Macgyver these things with whats in the junk box .
The capacitor perhaps some thoughts ? i was thinking it was not such a problem i had used them before with out a problem ,,, B/W CRT used with older fly backs i can't recall ever seeing a flyback capacitor used on the anode,isn't the tubes Anode act also like a capacitor ?
Before your post it has been on my mind reading some time back about pulling apart the newer colour tv flyback transformers bit of work but you can get the caps out of these.
Well i have the AC, DC wise i have a Diode that can handle the voltage ,Your thoughts on the capacitor use or not?
The construction of the little EHT voltage have to make it so its safe no sparking in its own little case under the CRT area position.

[Steve Anderson]

True, the combination of the CRT internal last anode coating and the external 'Aquadag' coating do form a capacitor. The Aquadag being at ground/0V. This can be several hundred pF on larger TV tubes and with the flyback transformer running at 15.625kHz results in a sufficiently smoothed supply, though not regulated.

On a smaller CRT like this one there may be a need to add some form of additional smoothing. Again this is an area where I have little experience.

Because this appears to be half-wave rectification the diode(s) PIV rating needs to be more than 14kV if your supply is to be 7kV. If you've used microwave oven diodes in the past successfully I suggest sticking with them. I don't think having many 1kV diodes in a string is a good idea.

The only thing nagging me is the speed of microwave oven diodes. These are intended to be used on 50/60Hz mains frequencies, I'm not sure how good they might be at several/dozens of kHz. I guess there's only one way to find out...

Steve A.

Afterthought...if you had four of these diodes and the output of the HV supply is truly isolated from ground a bridge rectifier would be better. Lower PIV rating required on the diodes, half the ripple, and no DC current in the windings. Even my local supplier has some 8kV diodes in stock which are quite fast, 100ns switching time. Around US$0.30 each in small quantities. Datasheet attached.