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 Post subject: FT-243 Crystals
PostPosted: Feb Sun 12, 2006 6:41 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 82
Location: Michigan
I built a 1939 ARRL Design 10 watt cw TX using a 6L6 tube.<P>Anyone know where I can purchase FT-243 crystals ? (3.550 to 3.580 mhz )<P>Thanks<BR> <P>------------------<BR>Milt


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 Post subject: FT-243 Crystals
PostPosted: Feb Sun 12, 2006 8:04 pm 
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Location: Maryland 20709, USA
Hi Milt,<P>Cool <IMG SRC="http://antiqueradios.com/forums/cool.gif"><P>The FT-243 package is military, WWII vintage. It was never available commercially that I know of. The FFF equivalent (same pin diameter & spacing) is the HC-6/U hermetically sealed can. But of course it doesn't look like an FT-243.<P>You'll find FT-243s at hamfests and on evilpay. But they command a rather stiff premium, particularly those in the ham bands. If you can find one just outside the band you can move it a bit.<P>------------------<BR>73 de Leigh W3NLB | | Leigh@AtwaterKent.Info<BR><A HREF="http://www.AtwaterKent.info" TARGET=_blank>http://www.AtwaterKent.info</A> | | <A HREF="http://www.Synchrophase.info" TARGET=_blank>http://www.Synchrophase.info</A>


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 Post subject: FT-243 Crystals
PostPosted: Feb Sun 12, 2006 8:05 pm 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34328
Location: Sandpoint, IDAHO 83864
If that is the circuit I think it is, where the lone 6L6 is used as a Tri-tet oscillator, I would strongly suggest putting a #49 or equivalent pilot bulb in series with the crystal. The bulb will act as a fuse and protect the crystal if you mistune the transmitter.<P>That is one of the major drawbacks to the Tri-tet circuit. If the plate circuit should accidentally tune to the cathode circuit, at resonance the crystal current rises excessively and will shortly fracture your crystal. The Tri-tet's advantage is its rich harmonic content, so you could operate several bands off one crystal.<P>I don't like that "rock crusher" circuit because that is what it is. I have always had good performance using the Colpitts circuit, also know of as the "grid-plate" type of circuit.<BR>Curt<BR>Edit: Leigh and were doubling. Leigh- I have lots of commercial FT-243 crystals in my collection. JAN Crystals, Peterson Radio, Bliley,and several others.<P>Also, a NE-2 neon bulb without any series resistor can be wired in parallel with the crystal to offer protection.<BR>------------------<BR>Curt, N7AH<BR>(Connoisseur of the cold 807)<BR>QCWA# 25085 AMI# 242<BR>CW forever


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 Post subject: FT-243 Crystals
PostPosted: Feb Sun 12, 2006 8:11 pm 
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Leigh wrote:
<font>quote:</font><HR>Originally posted by Curt Reed:<BR><B>...The Tri-tet's advantage is its rich harmonic content, so you could operate several bands off one crystal....</B><HR>
<P>Hi Curt,<P>We did it again <IMG SRC="http://antiqueradios.com/forums/biggrin.gif"><P>That's great news! Our advertising department can do great things with that feature <IMG SRC="http://antiqueradios.com/forums/biggrin.gif"> <IMG SRC="http://antiqueradios.com/forums/eek.gif"><P>Now that you mention it, I have seen commercial rocks in FT-243 holders also. I suppose they had lots of holders in the pipeline after the war and continued to use them.<P>------------------<BR>73 de Leigh W3NLB | | Leigh@AtwaterKent.Info<BR><A HREF="http://www.AtwaterKent.info" TARGET=_blank>http://www.AtwaterKent.info</A> | | <A HREF="http://www.Synchrophase.info" TARGET=_blank>http://www.Synchrophase.info</A>


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 Post subject: FT-243 Crystals
PostPosted: Feb Sun 12, 2006 8:19 pm 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34328
Location: Sandpoint, IDAHO 83864
Leigh- in fact, there was an outfit who would put a crystal in your holder if you sent them the holder. FT-243's have been obsolete for many years and a lot of hams like the looks of the FT-243's over the hermetically sealed units, and I am one of them. I just wish I could remember who it was who was offering this service about ten years ago. I got rid of a lot of my FT-243 rocks that were surplus in the 5 to 6 mc range to guys who would send them to this outfit and get ham band rocks installed in them, especially for the AM frequencies on 80 and 40 meters.<P>The modern rocks just can not stand the gaff of some of the older tube circuits, especially with the 6L6.<P>In almost all the transmitters I used to build, and there were over two dozen of them, I standardized on the 6AG7 in the Colpitts circuit. Even sluggish crystals always seemed to start fine without any chirp if the variable capacitor in the cathode circuit was adjusted properly. Crystal current is lower than with other tubes and you can tune the plate to exact resonance without affecting the keying characteristics. Most circuits and tubes will cease oscillating when the plate is tuned to resonance and require it to be tuned to a slightly higher frequency.<BR>Curt<P>------------------<BR>Curt, N7AH<BR>(Connoisseur of the cold 807)<BR>QCWA# 25085 AMI# 242<BR>CW forever


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 Post subject: FT-243 Crystals
PostPosted: Feb Sun 12, 2006 10:32 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 109
Location: Carlin, Nevada, USA
You guys remember taking FT243's apart and rubbing a graphite pencil on the crystal to trim freq? My first transmitter (age 13, long ago) was that 6AG7 - 6L6 rig from QST and several years of the ARRL Handbook. Think I had more fun on 40m CW with that than any of the fancier rigs I bought/built later.<P>If I can find the carton in this mess here, I might still have some ham band 243's that I'd sell or swap. Also used to break pins off burned out octal tubes and stick them on the military holders to fit FT243 socket. Some military rig or another used to use what I remember as an FT241(?) holder, a little squatter and fatter than a 243, but with the same pin size and spacing. I bought several of those from my friendly neighborhood surplus store very cheaply. Texas crystals, sold by dealers, were often reworked military holders with stick on labels. You guys are bringing up stuff I had forgotten about for years. Thanks for helping me dust off the cobwebs.<P>------------------<BR>Ron Grube<BR>repair biz since 1962<BR>ex-WA6AUA, N7CI, '58-'85


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 Post subject: FT-243 Crystals
PostPosted: Feb Mon 13, 2006 12:15 am 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34328
Location: Sandpoint, IDAHO 83864
Ah, yes, I recall the FT-241 holders and their low frequency crystals that were multiplied something like 54 times to the operating frequency. That was necessary to get enough audio swing in the early FM sets that used them. <P>The lead pencil trick would work for a while, but as the crystal vibrates, the added carbon or whatever pencil lead was made of falls off, so your frequency slowly increases to what it was before you applied it. Often it took several months to do it, thou.<BR>Curt<P>------------------<BR>Curt, N7AH<BR>(Connoisseur of the cold 807)<BR>QCWA# 25085 AMI# 242<BR>CW forever


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 Post subject: FT-243 Crystals
PostPosted: Feb Mon 13, 2006 1:57 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 606
Location: Terre Haute, IN USA
Leigh says <BR>"The FT-243 package is military, WWII vintage. It was never available commercially that I know of."<BR>While it IS correct it was a mil designation and the holder actually PREdates WW2, several companies offered (note PAST tense) the FT243 as late as the mid 1970s. One was Texas Crystals--later to become part of JAN Crystals in Fort Myers, Florida, I have 5 FT243s all in the 40 meter ham band that I purchased as a Novice in 1969.<BR>International Crystals used to offer the HC6U holder with larger pins, which would fit perfectly in a FT243 socket. Many of this type were used in commercial 2-way radios, such as the U43GGT Motorola, better known as the "T-Power" The crystal oven socket in this radio was nothing more than a DUAL FT243 socket, with one pair being the crystal, and the other pair being the voltage for the crystal oven. As of last year, International Crystal can no longer make this crystal due ONLY to their inability to locate a manufacturer of the larger pins, which were nothing more than slip-on-and-solder OVER the smaller wire pins.<BR>It takes a bit of effort, but I have disassembled a FT243, removed the unwanted crystal and holders, then soldered a HC25 holder crystal to the pins. The inside of the FT243 has to be enlarged slightly to fit a HC25 holder, but it's nothing more than using a small Dremel grinding tool for a few moments.<P>------------------<BR>


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 Post subject: FT-243 Crystals
PostPosted: Feb Mon 13, 2006 2:03 am 
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Location: Somers, CT
I wouldn't use any crystal slab smaller than what is used in the FT-243 holder! Any of the metal hermetically sealed crystals will probably overheat and fracture when used in a 6L6 oscillator. Too much RF current through the wafer.<P>Also, like Curt noted: some of those designs were rock crushers from the get go. <P>Pete<P>------------------<BR>


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 Post subject: FT-243 Crystals
PostPosted: Feb Mon 13, 2006 2:25 am 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34328
Location: Sandpoint, IDAHO 83864
You better believe it Pete! The newer smaller crystals are wimps as compared to what we used to use! <P>For the other hams here....Have any of you used the REAL old style rocks? I mean the ones that you ground your self after ordering a blank from one of the manufacturers that was "close" to your desired frequency? I think they were made by Bliley. I have a couple 160 meter crystals that are an inch square and nearly a quarter inch thick! I also have some 80 meter rocks that are 1" square and about 1/8" thick. Those things are massive! The holders are round and fit a five pin tube socket and the cover screws on and off.<P>Now those things are the real McCoy when it comes to crystals!<P>I would not be afraid of using them in the single tube 813 transmitter that was on the rear cover of QST for a while back in the late 40's. Imagine a single 813 pumping out a couple hundred watts rockbound without a separate oscillator tube! I guess it was an outgrowth of the lone 6L6 design taken to the limit!<BR>Curt<P>------------------<BR>Curt, N7AH<BR>(Connoisseur of the cold 807)<BR>QCWA# 25085 AMI# 242<BR>CW forever


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 Post subject: FT-243 Crystals
PostPosted: Feb Mon 13, 2006 3:02 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1852
Location: Potomac, Md.
Avery wrote:
<font>quote:</font><HR>Originally posted by goradio:<BR><B>I built a 1939 ARRL Design 10 watt cw TX using a 6L6 tube.<P>Anyone know where I can purchase FT-243 crystals ? (3.550 to 3.580 mhz )<P>Thanks<BR> <P></B><HR>
<P>Milt, I've got a 3.570MHz FT-243 you can have for $8 shipped. It should be good in your circuit (hope there's not TOO much current going through the rock!), but if not let me know and I'll refund your bucks.<BR><P>------------------<BR>Avery W3AVE


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 Post subject: FT-243 Crystals
PostPosted: Feb Mon 13, 2006 3:58 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 82
Location: Michigan
goradio wrote:
<font>quote:</font><HR>Originally posted by Avery:/b]<HR></BLOCKQUOTE><P>Milt, I've got a 3.570MHz FT-243 you can have for $8 shipped. It should be good in your circuit (hope there's not TOO much current going through the rock!), but if not let me know and I'll refund your bucks.<P>[/B]<HR>
<P>Yes, Avery,check your e-mail.<BR> <P><BR><P>------------------<BR>Milt


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 Post subject: FT-243 Crystals
PostPosted: Feb Mon 13, 2006 4:17 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 82
Location: Michigan
goradio wrote:
<font>quote:</font><HR>Originally posted by Curt Reed:<BR><B>If that is the circuit I think it is, where the lone 6L6 is used as a Tri-tet oscillator, I would strongly suggest putting a #49 or equivalent pilot bulb in series with the crystal. The bulb will act as a fuse and protect the crystal if you mistune the transmitter.<P>That is one of the major drawbacks to the Tri-tet circuit. If the plate circuit should accidentally tune to the cathode circuit, at resonance the crystal current rises excessively and will shortly fracture your crystal. The Tri-tet's advantage is its rich harmonic content, so you could operate several bands off one crystal.<P>I don't like that "rock crusher" circuit because that is what it is. I have always had good performance using the Colpitts circuit, also know of as the "grid-plate" type of circuit.<BR>Curt<P>Also, a NE-2 neon bulb without any series resistor can be wired in parallel with the crystal to offer protection.</B><HR>
<P>Curt<BR>Yes, it is a lone 6L6. I was unaware of the "rock crusher" reputation. I have an in line meter and never go past 25 mills when loading into antenna with my existing FT-243 crystals I have for 80 & 40 meters. <P>I do have one HC-6/U crystal in freq. range I desire, but did not try because I thought it was not sturdy enough ? <BR>If I put the #49 in series as suggested, will this be adequate ?<BR>Thanks <P>------------------<BR>Milt


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 Post subject: FT-243 Crystals
PostPosted: Feb Mon 13, 2006 6:03 am 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34328
Location: Sandpoint, IDAHO 83864
Yes, as the bulb serves as a fuse and too much excitation will cause the bulb to burn out, saving the crystal.<BR>Curt<P>------------------<BR>Curt, N7AH<BR>(Connoisseur of the cold 807)<BR>QCWA# 25085 AMI# 242<BR>CW forever


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