Hi

There are two things you may be talking about:

1) The pressure springs on things like FT-243 holders, they are generic springs.

2) The connection leads on plated blanks, they are indeed strange *and* 
soldering to the blank is a big problem. 

I’m guessing you are in bucket number 2. 

Bob


> On Jun 4, 2016, at 1:41 PM, Mike Cook <michael.c...@sfr.fr> wrote:
> 
> Thanks all for your advice, hints, tips and links. Lots to read , do and some 
> hardware to check.  I don’t have a frequency generator so I’ll have to go 
> another route. 
> 
> Oh. One last Q. Has anyone tried repairing the « spring » wire electric 
> connections on large quartz plates. In one large unit I have they had 
> corroded and dropped the plate, luckily no damage.  I have done one, but I 
> have no Idea what the original wire composition was so have certainly induced 
> some stray capacitance/resistance. It is possible that it was a filter rather 
> than a frequency source as it was not in a vacuum. 
> 
> Have a good one.
> 
>> Le 4 juin 2016 à 18:49, Bernd Neubig <bneu...@t-online.de> a écrit :
>> 
>> 
>> Tim Shoppa wrote:
>>> The Pierce logic-gate-biased-active oscillator is pretty reliable to start 
>>> and will oscillate somewhere with most crystals from kHz to MHz.
>>> As you found out, it will often come up on one of many overtones.
>>> To reduce chance of coming at an overtone, a series resistor from logic 
>>> gate output to the crystal is often enough. If not, a RC low-pass will cut 
>>> down even further (although of course adding phase shift.)
>> 
>> This is certainly the easiest and fastest way for a go/no-go test and to 
>> find the approximate resonance frequency. 
>> In the attached circuit diagram make CX1 and CX2 about 10 pF and RGK several 
>> MegOhms.
>> The inverter gate should be preferably an unbuffered HCMOS or other fast 
>> inverter.
>> For crystals in the MHz range you can replace RV by a short, for kHz 
>> crystals make it a few kOhms. If testing small watch crystals @ 32768 kHz or 
>> around, RV should be 100 kOhm at least. RV reduces the crystal drive level 
>> (RF current) to an acceptable level to avoid overloading or even damaging of 
>> the crystal. For low frequency crystals the RV-CX2 lowpass also avoids 
>> start-up at the overtone.
>> It is recommended to add a second inverter gate at the output to isolate 
>> your oscilloscope or counter input from the oscillator stage. Add some >330 
>> ohm in series to the output of the 2nd inverter, if you connect a coaxial 
>> cable. Then terminate the coax at the oscilloscope or frequency counter end 
>> with 50 Ohms, so the square wave form will be roughly maintained.
>> 
>> In this circuit the crystal will not operate at its series resonance, but at 
>> a load resonance with load capacitance of something between 8 pF and 10 pF 
>> (depending on the inverter input and output capacitance plus the stray 
>> capacitances of your test fixture).
>> If you want to operate the oscillator at a (low) overtone, such as 3rd (or 
>> maybe 5th), you must add a series combination of 10 nF plus an inductor in 
>> parallel to CX2. The 10 nF is to avoid DC short-circuiting of the output. 
>> The inductor together with CX2 must have a resonance frequency mid between 
>> fundamental mode and 3rd overtone (not at one of them). So the tuned circuit 
>> acts like a capacitor at the 3rd OT and is inductive at fundamental mode 
>> (thus the phase condition for oscillation is not fulfilled at the 
>> fundamental mode)
>> Have fun
>> 
>> Bernd
>> DK1AG 
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> 
> "The power of accurate observation is commonly called cynicism by those who 
> have not got it. »
> George Bernard Shaw
> 
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