The AM Forum

I have an FT-243 crystal that was working fine last week but now has quit. Any tips or ideas on getting it working again?

Thanks,

Steve N4IOR

Steve,

More info needed.  Is this a real FT-243 or a holder with a smaller modern crystal mounted inside?

Are you sure it is the crystal and not the transmitter?

Is this a fairly low power oscillator or one that potentially eats crystals if not properly tuned?

Many times a real FT-243 blank can be returned to health by dis-assembly, careful cleaning of the crystal and its contact pieces with alcohol, drying, and careful reassembly.

Hi-

It is a real FT-243. I opened it up and tried cleaning with alcohol. I also tried another crystal and the oscillator is working.

I think the oscillator is low powered and is a reasonably modern design (mid 60's)- not like some of the single tube CW transmitters which I have heard are hard on crystals.

If you tried cleaning and had no success, it could be that the crystal has fractured. If possible, try the crystal in another circuit. Also make sure the pins are reasonably clean and the internal pin connections are good.

What oscillator circuit is it failing to oscillate in? If in a commercial rig, what model/make? IS the crystal intended to operate on its fundamental or an overtone? If it is in the usual FT-243, and under 10Meg region, then try building up a series feedback type using a cmos logic gate with a 9volt battery supply. use a 74HC04, or CD4049, etc.

The oscillator is in the transmitter section of a Lafayette HA-460 6m rig.

8 MHz 3rd overtone-type crystal.

Pete,

I'm puzzled by your reply, so please help me out here. I always thought that 8 MHz crystals for six meters were operating on their fundamental frequency, and that the oscillator output was tripled and the doubled to get to 50 MHz.

If the 8 MHz rocks were running on their third overtone, does that mean that their fundamental frequency was 2 MHz?

Thanks in advance.

Bill, W1AC

8 mhz crystals oscillating on the third overtone.  A crystal that is marked 24 mhz is most likely a 8 mhz rock.

I got it working again. I took it apart again and checked the connections to the contact plates. Then I reassembled it, cleaned the pins a little with some fine steel wool and plugged it in. Didn't work at first but I tapped it once or twice and now it is working again like gangbusters.

 Thanks for all your advice and help.

Steve N4IOR

Whew! Your lucky. I cracked four of them bAck in my JN days feeding a single 6146 HB.  Not even an 813.  Also got a prized OO report for out of band dirt.  After I opened the first one i literally saw a crack, didn't bother to open the rest.  Big tears at $4.95 old for them back then.  Gotta be same as $50 new now. :-[

My luck was short lived- it quit working again.
I need to open it up and try again I guess.

What was it ground for, Hz wise?

I have lots of original FT-243 8 mHz rocks, maybe something here will help.

73DG

8400 kc- using it for 50.4 on 6m

Crystal(s) 50 KHz either side of 50.4 would still work fine and probably most wouldn't know the difference. Having only one crystal is a disadvantage. Band opens, 20 hams start calling CQ or holding a QSO on 50.4 and it's a wall of noise and QRM.

I use crystal mostly for net use on 6. I use a Lafayette HA-460 so I have a built in VFO as well.

Dennis, W7TFO, sent me some rocks that got me going again.

Thanks Dennis!!

Steve