5AHP7A Vintage SSTV The Deep image

[Steve Anderson]

Jeez, what were these guys smoking in the 70s? Pin 3 and pin 11 of the 74123 need pulling high. This is not shown on the diagram...at least jiggered if I can see it. Now it depends on what version of the '123 you're using. Others correct me here if I'm wrong, but the original 7400 series required a 4k7 pull-up, you couldn't simply wire it to Vcc as per all the more recent stuff.

Upshot, Harry pins 3 and 11 of all '123s need pulling high...somehow. Simply replace the 74123 with a HC version and be done with it.

This diagram should be shot (in fact the author) twice a day for a fortnight.

Steve A.

Don't know what a fortnight is? Two weeks, 14 days.

[Steve Anderson]

Looking further down the line I've seen another error, and I'm sure it won't be the last. To be honest Harry, give up on this crap.

I have to temper that a bit as the idea of gating the sync pulse such that an erroneous bit of garbage doesn't cause a mis-trigger both in vertical and horizontal has much to be commended.

You can imagine the Editor, "Don't shoot me, I'm only the messenger."

Steve A.

[Harry Dalek]

Looking further down the line I've seen another error, and I'm sure it won't be the last. To be honest Harry, give up on this crap.

I have to temper that a bit as the idea of gating the sync pulse such that an erroneous bit of garbage doesn't cause a mis-trigger both in vertical and horizontal has much to be commended.

You can imagine the Editor, "Don't shoot me, I'm only the messenger."

Steve A.

I am Starting to wonder my self perhaps listening might help here for further disappointment ....i need a game plan ....I think i will reboot and think about deflection side of things ..as i wanted to do so i can get the CRT working curse of the reboot has struck again ! .

Out of interest what have you seen that you think is OK my second choice was Ralph's in parts as in like the deflection amplifiers .

Edit looking at the front end of it Steve your redesigned robot circuit looks good i forgot about that ~!

[Steve Anderson]

To be quite frank and brutally honest, let's start again as per the 3BP1.

The power supplies you have already done, good. The problem in using 70s designs is you're going to get 70s results, which were impressive at the time, not now. Plus there's the headache of getting the parts these days.

More tomorrow, I'm the chef for this evening...no jokes please...

Steve A.

[Steve Anderson]

Moving on with this...I'm looking into the CRT circuit. You've already got the several kV you need for the final anode, now it's down to the few odd hundred volts for the grid/cathode/focus part.

Now I note that there's a remark on the Du Mont datasheet for this CRT (attached) about a 'beam alignment magnet'. See note 7 on the second page. No other datasheet for the 5AHP7 I have mentions this. So presumably it operates without one, but this fine-tunes the focus somehow. Something to bear in mind for later.

Harry, what's the no-load voltage of the power supply for this - the +360V or so rail used before for the 3BP1 deflection circuits amongst others? The load this time is going to be a lot less than before so I'm hoping it will come up to somewhere around +400V. It's not the end of the world if it doesn't.

Steve A.

[Harry Dalek]

Moving on with this...I'm looking into the CRT circuit. You've already got the several kV you need for the final anode, now it's down to the few odd hundred volts for the grid/cathode/focus part.

Yes but yet to be used in anger !

Now I note that there's a remark on the Du Mont datasheet for this CRT (attached) about a 'beam alignment magnet'. See note 7 on the second page. No other datasheet for the 5AHP7 I have mentions this. So presumably it operates without one, but this fine-tunes the focus somehow. Something to bear in mind for later.

I have not noticed this on the other data sheets i will look if the others mention it ...
I can't find it but i know i have seen a yoke with 2 magnets either side of it theres another old one i have that looks like it has but does not seem magnetic or its very weak ....now this is some thing as you say to remember .

Harry, what's the no-load voltage of the power supply for this - the +360V or so rail used before for the 3BP1 deflection circuits amongst others? The load this time is going to be a lot less than before so I'm hoping it will come up to somewhere around +400V. It's not the end of the world if it doesn't.

Steve A.

The power supply is pretty much as in Ralph's circuit apart from i have like 2 watt 156k load resistors around both rails on all 4 caps as i wanted to discharge the power supply caps and i suppose it drops the voltage a touch but i used 2 1 meg or so 2 watt resistors on the positive and negative ends to drop 36 volts on the positive side .

So looking at Ralph's circuit at the first cap its 362 volts second its 352 and around the 1 meg resistor its 316 on the positive and 312 on the negative ...as i was trying to get to 300 volts ...with out the load resistor if you call them that its it would be up the 380s 90's DC..

I will took at the transistor now give you a list

[Steve Anderson]

OK, +380V or thereabouts is going to be fine, I'll start pulling together the CRT bit. In this case you're not going to be needing the -300V, only the positive.

...hang on a sec! I had forgotten (again) you've got -320V (or so). Now that makes things a lot easier!

I wonder why Ralph only used half-wave rectification? If your transformer is centre-tapped as per Ralph's drawing adding two more diodes would boost the voltage (slightly) but with half the ripple. It's worth the extra cost of two 1N4007s.

Steve A.

[Harry Dalek]

OK, +380V or thereabouts is going to be fine, I'll start pulling together the CRT bit. In this case you're not going to be needing the -300V, only the positive.

OH not much needed changed about there ,i think it would be 386 volts if it ends up the same as the 3bp1 monitors from memory .

...hang on a sec! I had forgotten (again) you've got -320V (or so). Now that makes things a lot easier!

Yes thats good power supply second negative half is there dual HV power supply ...have run all the power supplies for some time and work fine !

I wonder why Ralph only used half-wave rectification? If your transformer is centre-tapped as per Ralph's drawing adding two more diodes would boost the voltage (slightly) but with half the ripple. It's worth the extra cost of two 1N4007s.

Steve A.

May be the cost of them back then ? i have to look at the other monitor circuits what they did ...i have many of those so its not a problem to put them in i will whack them in next shed visit .

This version of the data sheet also mentions the magnet in the 5AHP7 but not in the A version which does mention the danger of to high a anode voltage YAKES!

Another birthday eventing day as i say tomorrow so have little time tomorrow but next few days the soldering iron is getting a work out .

[Steve Anderson]

As for the half-wave rectification, maybe it was good enough in the application it was being used for, the extra few volts not required, and what ripple there was had no visible effect. But to add the extra diodes the transformer does need to be truly centre tapped as per the drawing.

The magnet thing is unusual in tubes of this size, it's a case of we'll see when the time comes - you may have to plunder the kids collection of fridge-magnets!

The warning regarding X-rays needs to be heeded, but generally you need voltages in excess of 10kV to produce any that could be of concern. At your 7kV all should be well. An a**e-covering exercise by the manufacturer I think.

Steve A.

[Harry Dalek]

As for the half-wave rectification, maybe it was good enough in the application it was being used for, the extra few volts not required, and what ripple there was had no visible effect. But to add the extra diodes the transformer does need to be truly centre tapped as per the drawing.

The magnet thing is unusual in tubes of this size, it's a case of we'll see when the time comes - you may have to plunder the kids collection of fridge-magnets!

The warning regarding X-rays needs to be heeded, but generally you need voltages in excess of 10kV to produce any that could be of concern. At your 7kV all should be well. An a**e-covering exercise by the manufacturer I think.

Steve A.

Yes its Center tapped it is just used the AC out of it a little different in the 3bp1...i will change it easy fix.

I have tiny magnets or some thing handy ,yes wait and see how well it focus go's later..

Yes i am always a bit ify on high voltages and stay below 10 kv makes me wonder all those years in front off our old B/w tv in the 60's i am sure that would of been up the 20kv Perhaps The Thunderbirds were X raying me at the time each morning before school.

[Klaas Robers]

don't worry Harry, B&W TVs had some 10 to 16 kV, while colour sets had 25 kV. Both had a screen of glass containing quite some lead and that screened the X-rays sufficiently. More problem arised from the back cone of the picture tube, but nobody was sitting behind the TV.....
For the 5 to 7 kV it is no problem at all. X-rays go with the 3th power of the voltage, as far as I remember.

[Harry Dalek]

don't worry Harry, B&W TVs had some 10 to 16 kV, while colour sets had 25 kV. Both had a screen of glass containing quite some lead and that screened the X-rays sufficiently. More problem arised from the back cone of the picture tube, but nobody was sitting behind the TV.....
For the 5 to 7 kV it is no problem at all. X-rays go with the 3th power of the voltage, as far as I remember.

Well thats pretty good to hear i was thinking they may have been a bit sloppy with safety back then.
Interesting about the xrays from the back of a picture tube first time i heard of this .
Time to do a little more work on this project today taking Steve's advice on the power supply.

[Harry Dalek]

A new start i have completed Steve's reworked Robot SSTV demodulator,the scope GIF is from the baseband output using also Steve's sstv reversing wave file ,i have not checked it all over yet but that looks promising ....
Well once again a reboot to complete a project which i suppose is a better result than hitting a dead end .

[Steve Anderson]

The two presets are:-

VR101 allows you to set the sync-tips to 0V or a small offset if needed.

VR102 sets the overall video amplitude. I tend to think of SSTV as being 1kHz/V so 2.3kHz - 1.2kHz = 1.1kHz, so I chose 1.1V from sync-tips to white level as a standard here in the absence of any other. You can choose what you like, it's the FM sub-carrier that does have standards.

To test this out properly you'll either need an accurate audio oscillator, a PC-based version (a few freeware versions out there) or use some generated wave files. I have generated a bunch that go slightly beyond the normal bounds of SSTV (attached), this allows you to chart the 'S' curve above if you should wish to.

This just confirms or otherwise the linearity under static conditions, but it's a start.

Set-up should be quite easy. Set both presets to midway, feed in 1.2kHz and set the output with VR101 (point 1C) to 0V, there'll be a small amount of ripple, centre it about 0V.

Feed in 2.3kHz and adjust VR102 to produce 1.1V, go back to 1.2kHz and check it's still at 0V.

That's it! If you want feed in the other frequencies and note the output voltage without changing anything except the file playing. With those numbers you should be able to generate a chart (Excel) or a graph by hand. You should end up with something very similar to the above version.

Steve A.

[Harry Dalek]

The two presets are:-

VR101 allows you to set the sync-tips to 0V or a small offset if needed.

VR102 sets the overall video amplitude. I tend to think of SSTV as being 1kHz/V so 2.3kHz - 1.2kHz = 1.1kHz, so I chose 1.1V from sync-tips to white level as a standard here in the absence of any other. You can choose what you like, it's the FM sub-carrier that does have standards.

To test this out properly you'll either need an accurate audio oscillator, a PC-based version (a few freeware versions out there) or use some generated wave files. I have generated a bunch that go slightly beyond the normal bounds of SSTV (attached), this allows you to chart the 'S' curve above if you should wish to.

This just confirms or otherwise the linearity under static conditions, but it's a start.

Set-up should be quite easy. Set both presets to midway, feed in 1.2kHz and set the output with VR101 (point 1C) to 0V, there'll be a small amount of ripple, centre it about 0V.

Feed in 2.3kHz and adjust VR102 to produce 1.1V, go back to 1.2kHz and check it's still at 0V.

That's it! If you want feed in the other frequencies and note the output voltage without changing anything except the file playing. With those numbers you should be able to generate a chart (Excel) or a graph by hand. You should end up with something very similar to the above version.

Steve A.

HI Steve
Run out of time today but i will do that test i do have PC software oscillators but i think its best to use your wav files
I have not done this test before so i will try and follow your procedure sounds interesting ,think its one of those things i need to try and see what results i get .
Should i get similar results to the chart
viewtopic.php?f=8&t=1926&start=315
i suppose i would expect my chart would start at o volts 1.2 khz and voltage below khz and rise with frequency as i test each higher frequency . ?
I am interested to see how well i copied your circuit .