Another Monitor schematic diagram 60s 70s ?

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Another Monitor schematic diagram 60s 70s ?

Postby Harry Dalek » Sat Feb 24, 2024 6:39 pm

Valves are Still interesting always like to get back some time once i build a stand alone power supply ,here is a nice little monitor design some one sent me years ago also round 1990 but this would be 60s or early 70s design perhaps more than likely reused in other SSTV books
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Last edited by Harry Dalek on Sat Feb 24, 2024 7:11 pm, edited 1 time in total.
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Re: Another Monitor schematic diagram 60s 70s ?

Postby Steve Anderson » Sat Feb 24, 2024 6:54 pm

I have a copy of that article, and I have two NOS (New Old Stock, i.e. unused and in unopened original packing) 5ADP7 CRTs. They were going to be used in "The Brute" SSTV monitor which I abandoned. Maybe one day I'll return to it. My version was going to be 'almost' all semiconductor though, except the CRT.

Steve A.

The reason for abandonment? It was too large, it took up a substantial amount of space. With better planning it could easily be made half the volume. One limitation is the CRT itself, screen to socket base it's about 17.5" or nearly 45cm long, plus (say) 2" or 5cm of clearence behind it. That's where I was hoping to squeeze the deflection amplifers in.
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Re: Another Monitor schematic diagram 60s 70s ?

Postby kd2bd » Tue Feb 27, 2024 4:34 am

That's a design created and published by Copthorne MacDonald, himself.

One of it's flaws is that there is NO subcarrier low-pass filtering following the full-wave sync detector (V2). So instead of triggering on the rising slope of each detected sync pulse, the Horizontal Trigger (V4A) triggered on the first detected half-cycle of the 1200 Hz sync subcarrier. The result was line-to-line jitter in the displayed images, even under ideal (closed circuit) conditions. You can imagine how much worse things became with some noise thrown in.

Cop realized this problem and tried to correct for it by employing a 1200 Hz sync Phase Setter circuit in his companion 7290 vidicon camera. But the problem was in the monitor, not the camera.

In the 1970s, Cop addressed this issue in great detail in his "CQ" magazine column as it was a common problem among many of the homebrew and commercially manufactured monitors and scan converters of that era.

Live and learn.


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Re: Another Monitor schematic diagram 60s 70s ?

Postby Steve Anderson » Tue Feb 27, 2024 11:34 am

Hmm, that's a bit of a 'drop-off' by Cop. I've not really studied the circuit in detail, I wonder how Cop missed it? Surely to develop something like this he must have had access to a 'scope? It really doesn't matter these days, even if someone were to replicate this today, it should be a relatively simple fix, even using tubes/valves.

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Re: Another Monitor schematic diagram 60s 70s ?

Postby kd2bd » Wed Feb 28, 2024 2:57 am

Correct, Steve. A suitable low-pass filter can be inserted between point 2 (Figure 2A) and point 2 (Figure 2B).

The full article was published in the March 1964 issue of QST magazine, and can be found here beginning on page 43: https://www.worldradiohistory.com/Archi ... 964-03.pdf

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