Jeffree cell

[Harry Dalek]

Not much progress this weekend, I built a crude lapping machine using an old window wiper motor, I looked all over for some cast iron to make the lap with but had to settle for aluminium, the power supply is from an old PC, they can deliver plenty of amps and have 3.3v, 5v, 12v, the green enable wire needs to be tied to negative, I may make a holder for the crystal to oscillate it across the surface as its very boring by hand.

Hi John

I had to google lapping i didn't know what it was but thanks to Wikipedia i understand now

So you are trying to get those Crystals nice and flat ? sounds like it will take a while .

Yes i use the old pc power supplies all the time i have one with the plugs connectors on the case for a nice spare portable power supply ..

I don't know how flat the crystal needs to be or how thin ?

[johnrpm]

Sorry Harry, I should have explained lapping, the general principle is that soft laps hard, the media embeds into the soft material and becomes a short term type of grinding wheel, the media or abrasive is constantly replenished.

The crystals need lapping because they are not very flat, and way to thick at about 2.5mm, if I tried to cut thin crystals they would probably break under the cutting forces, as the brass disk is cut from sheet material and is not perfectly flat, which creates side forces,
for radio work they must be very precise to get a specific frequency, but for the jeffree cell, at least according to the pdf, not so precise.

I have an old valve RF generator and hope to find the resonant frequency of the crystal by putting a resistor in series (with a meter across)to detect the increase in voltage at resonance, there may be a few frequencies that resonance occurs.

Any advise/ suggestions on this and the modulation of the cell would be very welcome.

[Harry Dalek]

Sorry Harry, I should have explained lapping, the general principle is that soft laps hard, the media embeds into the soft material and becomes a short term type of grinding wheel, the media or abrasive is constantly replenished.

The crystals need lapping because they are not very flat, and way to thick at about 2.5mm, if I tried to cut thin crystals they would probably break under the cutting forces, as the brass disk is cut from sheet material and is not perfectly flat, which creates side forces,
for radio work they must be very precise to get a specific frequency, but for the jeffree cell, at least according to the pdf, not so precise.

I have an old valve RF generator and hope to find the resonant frequency of the crystal by putting a resistor in series (with a meter across)to detect the increase in voltage at resonance, there may be a few frequencies that resonance occurs.

Any advise/ suggestions on this and the modulation of the cell would be very welcome.

Hi john ...Well thats good just needs to fit the bandwidth your trying for which worse case it should at least do NBTV.

How flat do they need to be you think or does it matter ?

Is the thickness of the crystal determine its frequency another thing i should google

Getting very close now john have you worked out if the crystal works how you are going to do the tank ..

Any case very interesting project john .