Category Archives: Projects

Making a simple crystal tester


Remember from my previous post in Restoring Heathkit IT-17 tube tester? Where I mentioned that I got a box of tubes for $20 buck!

Well, under this pile of tubes there are bunches these little crystal modules that was made for WWII radios communication equipment.

I wanted to get rid of them on ebay but I need some way of assuring that they are working and the frequency is still as accurate as marked before I list them.

After some research on Internet, I found couple of plans which can be build quite easily. I wanted to make some modification to the circuit to use 2N3904 since I have bunches of them on hand. After fiddling with it for a while in LTSpice, I got a working circuit.

I then use KiCAD to draw the circuit and create a PCB layout from it and here is the final circuit and PCB:

crystal_tester_plot PCB

Making the PCB

This time, I wanted to try the toner transfer method to create a polished and professionally looking PCB. However, my stupid Samsung laser printer keep on jamming and it is low in toner. The final laser printed PCB artwork has many flaws and some traces are spotty.

After transferring the toner to the copper clad, I have to manually use the permanent marker to cleanup these traces. After etching the PCB and installing the components, this is what I got.

IMG_9369 IMG_9367

Here the circuit is being used for the first time to test an unknown crystal, the green LED is lid to indicating that the crystal is working perfectly.

IMG_9372

One down, plenty more to go. 🙂

IMG_9365

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