Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Sep Mon 20, 2021 10:20 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 38 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: Grinding crystals
PostPosted: Jan Mon 07, 2013 8:25 pm 
Member

Joined: Sep Thu 20, 2012 3:42 pm
Posts: 483
Location: Salem, OR
Don't know if this is the proper forum for this topic, so direct me elsewhere if I am in the wrong place.

I am looking at grinding some FT-243 crystals to the lower end of 40 and 80 meters for use in a Knight T-60 transmitter. I'll get basic in my questions:

1. You grind to a lower freq, correct?

2. What type of compound is best for the job?

3. What is a typical range in freq that the crystal can be effectively ground? I am looking at crystals that are around 100-300 khz high.

4. What has been your proven technique for accomplishing the job?

Thanks in advance,
Marc


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Mon 07, 2013 8:29 pm 
Moderator
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 22483
Location: Somers, CT
Grinding a crystal reduces its thickness, and raises the mechanical resonant point. Grinding will RAISE the frequency, you can't lower it.

Most hams would be lucky to move a crystal several kHz before running into difficulty. You have to be extremely careful to maintain the parallel surfaces of the crystal slab when grinding them down. Most hams used a figure eight pattern when lapping crystals. I'm not sure what would be the best grinding compound; so I'll let a few others chime in... but a 100 kHz shift is an ambitious undertaking.

Pete

_________________
Just because it can be done doesn't mean it should be done.


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Mon 07, 2013 8:38 pm 
Member
User avatar

Joined: Jan Fri 06, 2012 8:47 pm
Posts: 7426
Peter Bertini wrote:
Most hams would be lucky to move a crystal several kHz before running into difficulty. You have to be extremely careful to maintain the parallel surfaces of the crystal slab when grinding them down.
Peter, I agree and have actually tried grinding FT-243 military crystals to try to fudge them into the ham bands (back in my Novice days). Always ended up with a failed crystal long before reaching my objective.

I had a bucket full of military crystals so figured it was worth a try, but it was a waste of time. I think I managed to move some 20 or 30 kHz, but that's about it.

Curtis Eickerman

_________________
http://curtiseickerman.weebly.com


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Mon 07, 2013 8:45 pm 
Member

Joined: Sep Thu 20, 2012 3:42 pm
Posts: 483
Location: Salem, OR
Thanks, gents, for the prompt replies. I may try it just for fun, but finding crystals cut to the lower end of 80 or 40 meters is a bit tough. I found a couple on ebay and they were pretty proud of them at $15 ea. Perhaps I am naive, but that seems a bit high. Any suggestions as to where I might find crystals would be greatly appreciated.

Marc


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Mon 07, 2013 8:57 pm 
Member

Joined: Sep Thu 20, 2012 3:42 pm
Posts: 483
Location: Salem, OR
Well, I may have been a little too critical of today's pricing. I found a 7025 khz for $10, and it covers 40, 20, and 15, and 10 meters pretty well. May still try the grinding thing in my spare time.

Thanks for the tips,
Marc


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Mon 07, 2013 9:01 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31285
Location: Maryland 20709, USA
I've always bought my crystals from International Crystal Manufacturing in Oklahoma City www.icmfg.com

Give them the equipment model number or a homebrew schematic and they'll send you the right crystal.

Great folks to deal with.

- Leigh

_________________
73 de W3NLB
http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Mon 07, 2013 9:47 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 30905
Location: Livermore, CA
You can go up in frequency grinding crystals. Very important to keep the crystal flat. Try grinding with powder, we used to use Ajax, and a little water. Do this on a piece of glass.

If you don't grind perfectly flat and keep surfaces parallel crystals will lose activity. At some point they no longer oscillate.

_________________
Norm


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Mon 07, 2013 9:52 pm 
Member
User avatar

Joined: Jan Fri 06, 2012 8:47 pm
Posts: 7426
Leigh wrote:
I've always bought my crystals from International Crystal Manufacturing in Oklahoma City http://www.icmfg.com
I don't think they do any FT-243 (almost HC 17/U) packages anymore (at least not listed), but you may be able to convert HC 50/U or 51/U that they do sell by using this procedure http://k4che.com/HC%206%20Convert%20pag ... 20page.htm (note HC 6/U, HC 33/U HC 50/U and HC 51/U all have almost the same spacing as the old FT 243, but just not the proper pin diameter or length).

Here is a lot of information about the package sizes and pin spacings for various crystal holders http://www.af4k.com/crystal_holders.htm .

Ultimately you are trying to get 0.5" pin spacing for .093" diameter pins if I remember correctly.

Curtis Eickerman

_________________
http://curtiseickerman.weebly.com


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Mon 07, 2013 11:11 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31285
Location: Maryland 20709, USA
Eickerman wrote:
Ultimately you are trying to get 0.5" pin spacing for .093" diameter pins if I remember correctly.
Hi Curtis,

I don't think anybody has made real FT-243 holders since WWII.
The pin diameter and spacing are what matter.

I have one in hand at the moment. Spacing measures .484" with a diameter of .093".
That seems odd, but the measurements are correct. Perhaps it's not a real FT-243 but looks like one.

I do remember that the FT-243 will fit in an octal socket (skipping one hole).
So I measured an octal socket and it does come out to 0.500" c-c.
Don't know where the discrepancy is. I remembered the spacing as 0.500" also.

- Leigh

_________________
73 de W3NLB
http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Mon 07, 2013 11:39 pm 
Member
User avatar

Joined: Jan Fri 06, 2012 8:47 pm
Posts: 7426
Leigh wrote:
I remembered the spacing as 0.500" also.
Yeah, the HC 17/U , CR 5/U or CR 6/U were the more modern equivalent for the FT 243 with about 0.485" spacing and .093" pins. The .015" difference on the spacing doesn't matter on the typical sockets that have more slop... I mean "allowance" than that. :)

I think all of these are also now obsolete.

Curtis Eickerman

_________________
http://curtiseickerman.weebly.com


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Tue 08, 2013 12:05 am 
Member

Joined: May Tue 30, 2006 4:46 pm
Posts: 10887
Location: Santa Rosa, CA
I tried grinding FT-243 xtals in my Novice days and couldn't really get any good results.

Read an article in QST about lowering xtal frequency. You simply rub one face of the crystal with a soft lead pencil and load it down with graphite... well, that was the theory. It would drop the frequency a few kcs. for a while. Was not a stable solution.

Some QRP transmitter designs use an "adjustable" circuit to change frequency a few Kcs. by varying the capacitance in series with the crystal.
Image

Rich


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Tue 08, 2013 12:38 am 
Member

Joined: Dec Sat 08, 2007 9:51 pm
Posts: 1475
Location: Nashville TN
My dad used to grind cystals using a plate glass window and toothpaste. He sometimes use Cloverdale valve grinding paste XXXX fine grit.Told me both worked well.IIsometimes still see thoses old xtals at out Antique radio swap meets but not like i used to.Sprman

_________________
Be happy ,enjoy life as its so short!


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Tue 08, 2013 1:36 am 
Member
User avatar

Joined: Mar Fri 14, 2008 1:40 pm
Posts: 6770
Location: SE USA
Hi,
Just chiming in with nothing but dittos. My grinding success has been rather pitiful. 20-30 kcs before I ruin it. And that's using all the various 'approved' methods. Some guys claim much better success but I don't think we regular guys can do it. $10-15 bux for an original FT-243 isn't a bad price these days - particularly if its a desirable frequency. You can get a nice VFO for the cost of a few rocks!

_________________
The beatings will continue until the morale improves


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Tue 08, 2013 2:42 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 16735
Location: S. Dartmouth MA 02748-1225 USA
Marc,

I found a little more information...

http://www.antiqueradios.com/forums/viewtopic.php?t=5470

http://www.hayseed.net/~jpk5lad/K5LAD%20Memories/Vols%2026-30/MemoriesVol28.htm

http://home.netcom.com/~wa4qal/crystal.htm

At wa4qal, extensive documentation of the progress of the grinding process has been documented. An impressive change of frequency of greater than 1.2mhz :shock:

I have an old photocopy of a reprint of the November 1957 CQ article "How to GRIND Crystals". There are a couple of useful ideas in the article that are not mentioned in anything I found on the web. I can scan it and send it as an image or a pdf to your email address.

FWIW I ground crystals some 50 years ago taking many short cuts. Out of three crystals, two failed to oscillate and one moved somewhat but lost a lot of its activity. I recall I made the mistake of grinding both sides :roll:

GL Marc

Chas

WA1JFD

_________________
List' & I will Enchant Thine Ear


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Tue 08, 2013 3:53 am 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 30905
Location: Livermore, CA
Rich

I transmitted FSK (Frequency shift keying). Used diode switching and caps along with a crystal. Almost all crystals would shift 425 cycles, some to around 1k. Don't remember any shifting much more than that.

_________________
Norm


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Tue 08, 2013 6:10 am 
Member

Joined: Sep Thu 20, 2012 3:42 pm
Posts: 483
Location: Salem, OR
Chas,

Thanks for the links. I'll keep this information handy. Will probably try it at least once to see how it works out.

Marc


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Tue 08, 2013 7:10 am 
Moderator
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 22483
Location: Somers, CT
The pencil lead trick will pull down the frequency, but the trade off is always reduced crystal activity.

Pete

_________________
Just because it can be done doesn't mean it should be done.


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Tue 08, 2013 10:06 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2895
Location: Olympia WA USA
Don't forget to wash the crystal carefully after grinding to remove all the "crud" before trying it back in the holder.
I have seen several xtal grinding articles, most of what was written was mentioned above.
One article mentioned using Comet ā„¢ cleanser for the grinding compound, besides some mentioning the tooth paste.

_________________
FrankB
WB7ELC
"The average family has 2.5 children. Where is the other .5 child?"


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Tue 08, 2013 10:53 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 30905
Location: Livermore, CA
Comet works, so does tooth paste. Tooth paste is slower. A person could start with Comet and finish off with tooth paste.

_________________
Norm


Top
 Profile  
 
 Post subject: Re: Grinding crystals
PostPosted: Jan Wed 09, 2013 3:16 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 25381
Location: Pocasset, Cape Cod, MA
It's always been a mystery to me how quartz could possibly be abraded with softer materials like household
cleansers or toothpaste.


Top
 Profile  
 
Post New Topic Post Reply  [ 38 posts ]  Go to page 1, 2  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 5 guests



Search for:
Jump to:  


































Privacy Policy :: Powered by phpBB