[Milsurplus] Crystal checker

[Kenneth G. Gordon]

On 30 Jul 2022 at 12:14, Bob kb8tq wrote:

> If you have un-plated blank versions, tossing them out probably isn´t a great
> idea. With some effort, they can be brought to life. The exception would 
> be parts that have been dropped and the blanks cracked ... no fix for them.
> 
> One thing that killed the original crystals back in WWII and still kills them is
> surface contamination on the blank. The fix they came up with back then still
> works today. Yes, it involves chemicals that will dissolve quartz. It very much 
> is *not* for folks who have any doubts about their ability / training in dealing
> with chemicals that can cause problems. ( Note: one can overdo this process
> and nuke the blank. Even done carefully, the frequency will go up a bit ...).
> 
> Since the electrodes in the original designs are just metal sheets, they *could*
> be replaced if they have failed in some way. Maybe not a quick fix. Certainly
> a "basement" kind of task. 
> 
> Bob

Yes, to almost all of the above.

I have used Whink (correct spelling) Rust Remover, available at your local supermarket, to 
both clean, and to "etch" crystals up in frequency. It contains 1% of that chemical Bob 
mentions above, HF.

And there was a rather detailed two-part article in Electric Radio Magazine on crystals, mostly 
FT-243 types, on how to "resurrect" those which had quit.

The author had discovered that by simply thoroughly cleaning the electrodes, many crystals 
could be reactivated, and some which were active already, had their output greatly increased.

Then, by cleaning the electrode, and the crystal blank, a dead crystal could be brought back 
to life.

But, to repeat, carefully and thoroughly cleaning the ELECTRODES often made a huge 
improvement, and in every case improved the output level of the crystal.

Now one thing to keep in mind about FT-243s is that the metal bits, the actual clamps, which 
touch the crystal have "raised" corners so that they touch the crystal only at the corners and 
leave a gap between the metal and the crystal at the center.

So by "cleaning" the electrodes means BOTH the "flappers" as Bob calls them AND the 
metal bits, the "clamps", which are between those "flappers" and the crystal blank. I.e. 
making the metal-to-metal contact as low resistance as possible. Or to put it another way, 
making the resistance between the holder pins and the crystal blank as low as possible

The author of the article above found that in many crystals, that resistance was much higher 
than one would suspect, and by elminating that resistance, the crystals worked much better.

In several cases, the electrodes themselves were covered with some sort of film, or corrosion 
which caused this high resistance.

Ken W7EKB