[Milsurplus] Metal to crystal bond

[hwhall at compuserve.com]

>2) Make up some blanks from a quartz bar
The "understatement" of that sentence reminds me of Steve Martin's skit, "How To Make A Million Dollars And Not Pay Any Taxes."  Step 1: "First, you make a million dollars."   :-D

WayneWB4OGM
-----Original Message-----
From: Bob kb8tq <kb8tq at n1k.org>
To: CL in NC <mjcal77 at yahoo.com>
Cc: Milsurplus <milsurplus at mailman.qth.net>
Sent: Thu, May 21, 2020 2:42 pm
Subject: Re: [Milsurplus] Metal to crystal bond

Hi

A FT241 (etc) is a very different electrical model than what you are used to buying 
these days. There is an air gap between the blank and the electrodes. That adds 
a series C to the model and reduces the “pull range” in a given circuit. 

The “open to the air” assembly, pretty much guarantees the crystal will age quite a bit. 
That approach died a fairly quick death when thin film electrode / sealed package parts 
came out.

Quick “how to” on a modern crystal:

1) Get some bases and some cans. If they are solder seal, great. If they are resistance 
weld or cold weld also get the welder for them.

2) Make up some blanks from a quartz bar

3) Put them in your thin film setup and plate on the base electrodes. ( possibly two 
different metal layers).

4) Move them over into the holders and glue them in place with conductive epoxy.
Cure the epoxy and clean everything again.

5) Put the assembly in a second thin film setup and monitor the crystal frequency 
while you put metal on it. When it’s “just right” stop the system (normally with a shutter). 

6) Pull it out of that system, clean it and bake it. Seal it up. 

There are a number of variations on the theme depending on just what sort of crystal 
you are trying to make. If you are headed into the “cool kids” area, most of the work
above can be done without breaking vaccuum. Figure a couple million for a system
that does that …..

Bob

> On May 21, 2020, at 4:44 PM, CL in NC via Milsurplus <milsurplus at mailman.qth.net> wrote:
> 
> I chased a few links on the process of putting metal on quartz, many of them are dated from the 80's onward with some really involved equipment.  But, how did they do it on FT241's back in the 40's?  A manual I bought from Tucker Electronics a couple years ago about a piece of equipment I have, included a type written in house procedure on crystal production, Q&A, and procedures to follow on the line at the Midland Company to tweak the frequencies of the crystals as they were checked after initial lapping to freq.  Does anyone know how the metal to quartz bond actually transfers the potential to make it oscillate, and would simple 'Super Glue' make a bond that would work?  I  sure there would be some compensation on grinding if Super Glue did work.  The 1934/35 QST's give a lot of info on grinding your own for FT243 style holders, including the formula for thickness to start from that is near the intended frequency and the design of a saw to cut quartz.
> 
> Charlie, W4MEC in NC
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