Retro SSTV anyone?

[Steve Anderson]

Folks, after the China trip and all the report writing and other BS, work has resumed on this little SSTV monitor.

It was getting a hindrance not having the real power supplies available, so that has been dealt with. Attached is the interim PSU circuit diagram with some notes included - they'll be removed in due course. Also a photo of the PSU board which for a CRT-based device is quite simple.

Upper left is the +285V supply, upper right is the +/-12V supplies, lower left -700V and lower right the additional -70V to generate -770V for the CRT grid bias.

As a result of a few tests I shall be using 12AX7s/ECC83s for the deflection amplifiers.

I tested the supplies with more load than they will actually need to supply, especially the +/-12V rails, final voltages should be a little higher than the interim ones here.

Steve A.

[Steve Anderson]

After yet another interruption, work has resumed. I made a start on the ECC83/12AX7 deflection stages this afternoon. The tricky bit is drilling/reaming (by hand) the 22mm holes required for the valve-bases. Results not bad methinks...

Steve A.

[Harry Dalek]

Hi Steve

I think this is the first time i have seen a valve on a PCB ! i did a google to see if it has been done before and i did get a few hits some looked neater than others but yours would be only strip board go i have seen ....bet the holes were tricky to do .

Great idea love the look of it might get others to get there valves out again .

BTW looking at your power supply does it matter how large or small the power supply transformers are for valves voltage supply ? in the past they were always large enough to kill you and i always wondered if the size was really needed ,during WW2 on planes they used high frequency transformers inverters to keep weight down on the planes apart from this and mechanical inverter ideas i haven't heard of any one miniaturising the power transformer for a valve radio or what ever .

[Steve Anderson]

Valves/tubes on PCBs were very popular in 60s TVs in areas where transistors hadn't quite taken over, primarily in the area of the line output/EHT supply stage. The bases were very similar to the usual ones, but had pins much like an IC instead of solder buckets or eyelets. (Photos below).

I have put valve/tube bases on stripboard before, the example below was for a NBTV CRT display I made some years ago. I admit I haven't seen anyone else do this but I'm sure someone has. The holes aren't difficult, drill a 6mm hole then using a hand-reamer gradually, carefully, open them up to 22mm (for this type of socket). Thankfully this is cheap SRPB board and not fibreglass.

Any transformer should be treated with reverence as it has raw 220V AC on its input side (unless it's something like a low-level audio transformer). On the secondary, it would have to be really puny not to be able to kill you, it only takes 30 mA across the chest and you're toast. So anything with a secondary voltage above 50V should be treated with respect. In theory the 70V 16Hz ringing voltage on an ordinary phone-line could kill you but most just feel a tingle and let go.

The transformer below is the 500V transformer for the -700V supply for this CRT - yes, it could well kill you.

But a bigger danger is the charge stored in the supply DC capacitors, even if the transformer is puny, once rectified and these capacitors reach 700V it's lethal - it's also DC.

But for decades before semiconductors we all got used to working with high voltages. One rule is when the equipment is switch on work with one hand behind your back or in your pocket, this lessens the chance of current across the chest, but it only lessens it.

Even when switched off CHECK the supplies have died down to zero, a capacitor in good condition can hold a lethal charge for days. It is good practice to put a 'bleeder' resistor across the capacitor to fully discharge them - but still CHECK, the resistor may have gone open circuit.

I don't want to put anyone off working with valves, you just have to be sensible about it.

Steve A.

[Harry Dalek]

Yes steve you really have to be aware working with valves and i have been shocked a few times in the past mainly repairing valve radios and yes it tended to be forgetting the power supply caps hold that charge i got into the habit of shorting out the caps when ever i wanted to work on them that helped !

It really is a different mind set you have to get your self into when working with high voltages .

i just been working on an inverter i put in a neon indicator so i don't forget its working .

One other thing when i was a boy Tandy electronics used to sell kits and one i made was a one valve am radio but it worked on lower battery voltages ,i think i still have the circuit and construction plan ,the valve was normal size but it looked to me like the anode was shiny Aluminium instead of steel.

I found the plan see below those were the days

[Steve Anderson]

Many portable radios made in the late 40s and 50s used 'battery' valves. These were specifically designed to use as little power as possible to preserve battery life. A typical RF pentode (1T4 as per your example) had a heater of 1.4V at 50ma so a single 'D' 1.5V battery would last a long time. The HT varied, from as low as your example of 22.5V (then a common camera flash-bulb battery) to 90V. Battery voltages commonly used were 45V, 67V and 90V.

Then there's the space-charge valves, these ran at 12V on the anode, yes 12V. The were specifically developed for use in automobiles. The way they work though is quite different from your average valve and is a lengthy subject in itself. These can be picked up in the US for pennies each, the socket/base will cost far more than the valve! But you don't have to worry about hundreds of volts! They are today a novelty, you wouldn't consider using one unless you just wanted to for the sake of it. One could say the same about my use of ECC83s/12AX7s in this CRT monitor, the MPSA42 transistor will do the job, probably better, definitely cheaper, no socket is required, it's smaller, lighter and doesn't require nearly 2W of heater power. But it's my whim.

I only have one rather grotty picture of the 1T4...this one was made by Tung-Sol which sounds like an Asian company but was actually a US manufacturer...

Steve A.

The next day...found a better 1T4 picture...

[Harry Dalek]

I had a look in my valve collection to see if i still had that 1T4 but must be long gone ...

The 12 volt versions sound interesting ,sounds like the evolution of the valve kept going after the transistor ,wonder how small they could of made a valve ?

Valves have one thing over solid state they are less vulnerable to nuclear EMP so i bet valve gear is kept some where just in case !

Any way good to see your SSTV monitor evolving ..

[Steve Anderson]

...sounds like the evolution of the valve kept going after the transistor ,wonder how small they could of made a valve ?
...less vulnerable to nuclear EMP so i bet valve gear is kept some where just in case !

Unfortunately the valve gear might survive, but would we?

Nuvistors were about the smallest mass-produced valves as a direct threat of the transistor. They had many plus points, especially their high-frequency performance. There were also 'pencil tubes'. I have examples of both but as yet to find any use for them! Even more conventional glass valves were shrunk in size.

Below is an example of a 7586 Nuvistor triode, a 6111A dual triode pencil-tube and a 9002 'shrunken' glass single triode.

Steve A.

[Steve Anderson]

The 12V space-charge valves were not efficient, the first grid was used to set up the space-charge within the inter-electrode space. The second grid became the control grid. I'm no expert in these devices but they used many mA of current. They were designed for use in cars, so what's an extra amp or two for a whole radio? Better supposedly than those old vibrator supplies. (No giggles please).

Anyway, a short time today allowed me to complete the deflection stages, testing will begin tomorrow.

Steve A.

[Klaas Robers]

Quite some time ago I placed a post in this thread about the old 7BP7 SST-monitor that I built in 1973. I promised to make photos of it, as it was still in my attic. In the mean time I made these three photos, just before I started to dismantle it.

Some weeks ago I got the chassis and cabinet of a Heathkit SB-500 transverter for 2-metres. The circuitry was removed completely, so it asked to use the remains for constructing an SSTV-monitor using the 5FP7 that was also carefully stored in the same attic, waiting about 40 years for this task. I will post photos about that process too, but now the old one, built on a wooden base and with a shiny wooden front.

Here and there it is still somewhat dusty.....

[Harry Dalek]

Quite some time ago I placed a post in this thread about the old 7BP7 SST-monitor that I built in 1973. I promised to make photos of it, as it was still in my attic. In the mean time I made these three photos, just before I started to dismantle it.

Some weeks ago I got the chassis and cabinet of a Heathkit SB-500 transverter for 2-metres. The circuitry was removed completely, so it asked to use the remains for constructing an SSTV-monitor using the 5FP7 that was also carefully stored in the same attic, waiting about 40 years for this task. I will post photos about that process too, but now the old one, built on a wooden base and with a shiny wooden front.

Here and there it is still somewhat dusty.....

Hi Klaas
Great to see it at last and it looks in pretty good condition for 40 years , i bet you got many a picture via the Short wave radio with that...

I think i had the same picture tube does yours have a focus coil ? as i mentioned a while back mine would slowly go out of sharp focus when the focus coil started to get warm .

BTW Is it still working ? i would love to see it fired up if you do a test run ....I am glad you are using another tube for the new monitor that old one should be a keeper !

I did a google on the Heathkit SB-500 transverter looks spot on for a sstv monitor case just have to cut out the part for the crt where the meter is ...


heres another home made monitor that came up when i did a search

http://www.wedidit.it/joomla/index.php/ ... television

[Klaas Robers]

Hi Harry,

I don't know if the wooden monitor still works, I did not fire it up, as I am going to reuse the boards for the monitor in the SB-500 cabinet. Then I take them into operation one by one and I will see in how far I have to do something on them after the 40 years. I never just fire up old equipment after such a long time. Electrolytic capacitors need to do that carefully with a slowly increasing voltage. That is exactly what I am going to do.

Both picture tubes, the 7BP7 and the 5FP7 have magnetic deflection and magnetic focussing. The deflection coils, an old 70 degrees TV deflection unit, carry permanent magnet rings for the focussing. They can be moved more or less close to each other to get the focus optimal. I am going to reuse that coilset again for the 5FP7 tube. If you had a focussing COIL then you should have kept the CURRENT contstant and not the VOLTAGE constant. With a constant CURRENT the focussing will not change when the coil warms up.

For getting a monitor into operation it is important that I have a signal source with correct SSTV signals. That is the first thing that I made in 1973. It took me quite some time before I found that circuits back. I need it too for the SB-500 monitor. It still works correctly and I am going to build it into the new monitor, more or less because SSTV signals are almost no more heard on the short wave bands. Now at least I should be able to demonstrate the monitor. I will see if I can record them digitally and place them also on this web site. We'll see. The signals are according to the 50 Hz standard (line freq 16 2/3 Hz, frame time 7.2 secs).

[Klaas Robers]

Harry, you are right. The picture tube got a large hole at the position where the meter was. Here is a photo that I made just after the space for the picture tube was made. There is still yet nothing more in the cabinet. The picture tube is sunk into the chassis, a lot of sawing...



I designed a nice 3D-printed cadre around the picture tube. I also have to 'close' almost all the old holes and drill at least 8 new holes for the monitor controls. It will get an appearance like the other Heathkit SB equipment.

[Steve Anderson]

Klaas, I have attached a .wav file that may help you get going. It's unfortunately at the US line-rate (15Hz) but as it's not an off-air recording it is 'clean'. It's only 60 seconds but you can loop it in your media player. It's 120-lines rather than the later 128-lines. There are no VIS codes, it's straight Copthorne McDonald standard with the 30ms frame sync. It's 'Reversing Bars' as I call it, the top half of the frame is white left, black to the right, the bottom half of the frame is the reverse.

I can make an EU version (16.7Hz) if you would like it. I need to do them for myself anyway so it's no problem to do it, it just would make me get it done sooner rather than later.

Steve A.

...no it's not, see postings of 15/08/2015...

[Harry Dalek]

Great reuse of a case Klaas , excellent idea to use that case for a slow scan tv .
i always have a look at our reuse shops at the local tips where people take their junk so it can be resold and not just put in a hole in the ground ...now and again you find some nice cases for projects and you get to scrap the parts .

The project case is the hard part for me if i have to make it as i am no good at that repurpose something is a bit easier /

Are you going to use this crt as well ?