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Old 16th Apr 2018, 9:20 pm   #1
Electrical Rod
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Default Some Military Crystals:

In the photo shows several old military crystals that I picked up many years ago. I have no idea what is good if any. My plans are to build some type of test signal generator, I do have a few schematics of simple designs to start with if any of these can be used. Several of these crystals have CW stamped on them and most of these crystals are in the 6000 kc-upper 8000 kc range. A couple of them are stamped 200 kc.
Any idea if any of these could be used for that purpose if they work?
Rodney
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Old 19th Apr 2018, 12:09 am   #2
FrankB
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Default Re: Some Military Crystals:

Those are in about the 40M ham band range. FT243 case. Mil. surp. stuff.

You can use divider IC's and such or make a multiplier to get the desired freq.

Those are the old style, openable cases.

So if you are daring;
Open one of them. To decrease the freq, rub the quartz blank with a pencil. The lead will lower the freq a bit. Be sure to clean the contact area and handle with rubber gloves, as not to get finger oils on it. Recheck freq, and let run for a bit. If it stays you did a good job.
To increase the freq. a bit, CAREFULLY place the element flat on a glass sheet and gently, very gently, rub it with scouring powder. Clean & rinse thoroughly, and reinstall in holder. You should have raised the freq a bit. This is a very finicky job, and may take a few tries to get it correct.
In the "Good old Days" we did this a lot to change the xtals freq, as they cost dearly to buy. Remember to note new freq. on the case too.
(I found myself O.O.B. in my novice days with a mis- marked one. Got a nastygram from an O.O.)
- if you do this, they are really fragile. I ruined a few myself in the learning curve.
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Old 19th Apr 2018, 6:12 am   #3
Radio Wrangler
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Default Re: Some Military Crystals:

The pencil trick isn't quite as satisfactory as grinding, so crystals on the low side were sought. Finishing grinding with jeweller's rouge gives a better surface finish and better Q. We used to grind surplus FT243 crystals to carefully chosen frequencies to make lattice type crystal filters for SSB.... EG the first version of G2DAF's receiver.

David
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Old 19th Apr 2018, 3:39 pm   #4
CambridgeWorks
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Default Re: Some Military Crystals:

I think way back in the 60s I used vim or ajax powder mixed with 3- in-1 oil to form a paste. Using a sheet of "ordinary" glass as I couldn't find plate glass. Rubbing around in a figure of eight movement. It required very careful cleaning off. I think I used carbon tetrachloride! Made at least one ssb filter this way. I agree, avoid handling with direct skin contact.
Rob
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Old 19th Apr 2018, 10:42 pm   #5
MrBungle
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Default Re: Some Military Crystals:

That sounds like fun. Will keep an eye out for some FT-243 crystals going for junk at radio rallies / ebay
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Old 20th Apr 2018, 2:26 am   #6
Electrical Rod
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Default Re: Some Military Crystals:

Not to worry about anything I have being sold on ebay, I have never had an ebay seller account and have no plans to open one.
Those crystals will go back in the same box that they have been in for a very long time; i`m retired now and started back building a few hobby electronic projects,, I kept a lot of parts over the past distant years.
But thanks for the crystal info.
I have the parts up for this one tube tunable audio oscillator that I think will be interesting, this oscillator uses a single 6LN8 valve and the stated frequency is 20-12,000 hertz.
I enjoyed the visit.
Rodney
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