How I grind FT-171 crystals

This forum is all about building and using World War II spy radio equipment, in particular the Whaddon MK-VII (Paraset). For other radios, separate forums can be set up - ask the Quartermaster.

Please communicate in English. If you don't speak English (well), use Google translate (https://translate.google.com/) to convert your language to English.
Other languages are allowed but you won't reach all our members.
Post Reply
Sa2clc
Posts: 6
Joined: 09 Feb 2020, 10:52

How I grind FT-171 crystals

Post by Sa2clc »

Yesterday I ground a crystal, purchased at the paraset shop and I decided to test different approach than I did last time.
This time I used 600grit paper made for wet sanding, which I positioned on a thick glass plate (an old TV stand that´s never been used becasue the TV hangs on the wall)
I position the blank on the paper, apply some water, and using my index finger, i make number 8 patterns across the paper with the crystal blank.
From previous grinds using 1200grit paper (which took forever) I quit counting the number "8's" and instead used a timer.
10 minutes of rubbing on 600grit shifted the crystal from 3380 to 3460khz, Another 8 minutes shifted us up about 60khz, settling in at around 3520khz.
from there I took it easy in 1 minute passes, until i reached the 3554khz goal.
To finish it off, I took 10 strokes on each chamfer of the crystal, cleaned it in alcohol, and reassembled it and called it good. all under 45 minutes.
Keys very well, with full output, even though I moved over 170khz.
User avatar
Parasetguy
Beheerder
Posts: 53
Joined: 21 Aug 2018, 15:32
Location: The Netherlands, Velp
Contact:

Re: How I grind FT-171 crystals

Post by Parasetguy »

Great! You gave a otherwise useless crystal a new life. How green is that?

regards, Henk - Parasetguy
Post Reply