Fabricating a crystal.

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dr pepper

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I recently wanted a low freq xtal for a project.
I found amongst my junk box a huge (4"x2") delay line which looks like it has a large chunk of quartz xtal inside.
Is this likely to be quartz, and is it feasible to chop some off and make an xtal out of it, anyone done something like this?
I have a mini mill and some diamond cutters so I have a chance of being able to shape it, though I've never machined quartz before, I suspect its as hard as a south end bouncer.
 
There are several types of delay lines.

Excerpt from https://en.wikipedia.org/wiki/Delay_line_memory
 
3v0 said:
There are several types of delay lines.
Click to expand...

But his is presumably a chroma delay line from a colour TV?, that you presumably know nothing about as they aren't used for NTSC (and is what cures NTSC's main defect).
 
This sounds interesting chaps - not something I'm familiar with (I'd imagine this sort of stuff is not seen in more modern circuits). Would anyone be kind enough to point us in the direction of more informartion (esp. as regards their use in TV chroma decoding)?

Sorry I can't help with your question as such, but it does occur to me that if you have a delay line then would it be possible to simply connect it in a loop with some gain, and have it oscillate in a Wien-bridge style? The frequency should then be as stable as the delay through the delay-line. Does that sound feasible?
 

Look up PAL decoding.

Essentially the major defect of NTSC is the colour hue of the picture, which varies depending on signal conditions etc. (hence the use of Hue controls on NTSC sets).

Crudely, to correct this a PAL decoder delays a line of chroma for 64uS and uses the next line to cancel out the phase errors and changes.

And no, delays lines haven't been used for many years now, the early ones were glass, and the later (smaller) ones were plastic.

Later chip sets used delays inside the chips, presumably digital delays?.

If you can find a schematic for the Thorn 3000 colour decoder, that was an entirely discrete design, quite simple and easy to understand.
 
dr pepper said:
I recently wanted a low freq xtal for a project..
Click to expand...
What frequency?
I have some low frequency crystals from my broadcast and ham radio days. Some are one inch in size. The old ham radio operators would sand a crystal to change its shape and frequency.
 
I recall hams increasing the frequency of crystal by patiently sanding them with a mix of kerosene and "Puloil" (gentle abrasive used to clean things in the kitchen).
 
I can remember doing that. We had a powder that mixed with water made kind of a rubbing compound. Put some on a glass plate and make figure 8's until you got the frequency just right.. I don't know why it was figure 8's and can't remember for sure which direction the frequency went. Up I think.
 

They explained that the 8 ensured to erode the whole surface equally. Go to check that, anyway...
 
I want to make a 200khz crystal filter.
I dont mind 10,000 year old technology, I'm 50,000 years old.
I'll make up a simple osc using a cmos chip and see what freq it'll oscillate at, 2 x 64uS period would tell me that its a telly delay line.
Judging from the other stuff the guy had I'd say its more likely to be from a 'scope.
Looking at the wikipedia article its just like the piezo version which they say is quartz, and it uses sound?, vibration is what I'd say at those freq's.
I also have the electric version shown at the end of the article, came from the same place.
 
The crystal is 3.5" long from the transmission point to the reflection point, so the wave travels 7" from transducer to transducer, it gives a ring nearly bob on 3.579 mc's according to my spectrum analyser (new toy) with a sweep or step excitation, so its telly tech, if I apply a square wave of 5kc 64uS after each rising edge I get a ring of 3.579 mc's.
So you were right nige.
Only I didnt know these things had tuned piezo transducers, looks like you can only exite it with 3.579 mc's to get the best signal, makes it kinda useless if all I can adjust is the delay time if it'll only work well at that freq.
I spose I could fab my own transducers on the xtal, but I'd have to research the practicality of that, might do it with a couple of cut up piezo speakers for 200 kc.
 
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Figure 8's so you smooth around the whole perimeter evenly, and the frequency will go up as the size will go down (oscillates faster the smaller you get, and is why you need LARGE crystals for low frequency, and why we used the 3rd harmonic overtone on our radios to obtain smaller crystals).

I used to work at a place that made crystals. They bought large quartz crystals and cut them (at an angle) on a diamond saw. Then they had two old eye glass lens machines they used to shape them. On the line, if the frequency wasn't quite right, the girls would use a pencil erasure to rub them until they fell into specs. Then they would package them.
 
I bet that has changed now, they'll be chucked out dozens a second.
This xtal is big, 3.5" by 1.5" by 3/8", so I have plenty to go at, I think figure 8's is the last operation, the first being a diamond cutter.
I think the 3.57 mc's peak is caused by the size of the surface where the wave comes from, it does seem to be a unlikely coincidence as that is exactly a pal tv line freq.
If I go ahead and mod this I'll make it too big and then I'll take the polishig advice, thats assuming the wave path only bounces once, if not then it'll be tricky working out how much to bash off the end, lopping off random bits could have a random effect.
 
dr pepper said:
I want to make a 200khz crystal filter..
Click to expand...
Now I know what you want! I must have misted it in post #1.

I have some 2 legged and 3 legged ceramic band pass filters used in IF sections. I know I was using some 200khz or 220khz filters for sending data down the power line.
I have some at 455khz, 10.7mhz, probably about 45 to 50mhz for TV and probably some at 100khz for narrow band receivers. If I can find them there should be some around 200khz.

I can't find a data sheet now.
 
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