has anyone ever tried to trim a ceramic disk capacitor ? - Page 1
Forum section: electronics / rf-microwave

author: coppercone2
author_rank: Super Contributor
timestamp: March 28, 2025, 08:30:57 am
content: So for a while I have been thinking about doing something with SLCC capacitors (available in various substrates), with etching or lasers or whatever.And I wondered about a simple idea (say for CMRR in a differential probe). Instead of trimmers, has anyone tried to say tune a ceramic capacitor with a diamond file or just scraping it with a scribe?I thought maybe someone out there maybe tried this before. It's kind of like filing resistors, or solder tuning shunts. It's a long shot but maybe someone just happened to try this out.I thought to make some kind of amplifier where the balance of capacitors can be measured while you work on them, dusting them with a file carefully. The perfect scribe would be a diamond on a ceramic or plastic shaft, kind of like a pro adjustment tool.

author: David Hess
author_rank: Super Contributor
timestamp: March 28, 2025, 10:41:34 am
content: I have seen it done with a Dremel cutting wheel.

author: coppercone2
author_rank: Super Contributor
timestamp: March 28, 2025, 11:39:50 pm
content: its alot cheaper then a adjustable capacitor , and it should not drift from mechanically moving the shaft

author: David Hess
author_rank: Super Contributor
timestamp: March 29, 2025, 05:41:29 am
content: Quote from: coppercone2 on March 28, 2025, 11:39:50 pmI think I saw it used to trim the temperature coefficient of a crystal oscillator.

author: coppercone2
author_rank: Super Contributor
timestamp: March 29, 2025, 04:12:53 pm
content: Do you mean those little pF capacitors on the sides of the oscillator or the crystal itself (it is a kind of capacitor)I assume this means you can some how modify the tempco of a capacitor by trimming it? Because I just imagined the absolute value changes.. how does that help with drift?

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: March 29, 2025, 04:21:32 pm
content: has anyone ever tried to trim a ceramic disk capacitor ?Capacitor no, but ceramic resonator yes.I used vanilla diamond grinding tools.

author: TimFox
author_rank: Super Contributor
timestamp: March 29, 2025, 04:55:15 pm
content: A problem with removing part of the area of the capacitor’s dielectric is that it is irreversible, making tuning difficult.When doing similar surgery on a quartz crystal (increasing its resonant frequency), one can reverse it a bit by adding material such as with a pencil.

author: coppercone2
author_rank: Super Contributor
timestamp: March 29, 2025, 04:58:06 pm
content: thats why I thought single stroke diamond file, slow as shit but very gradual.

author: David Hess
author_rank: Super Contributor
timestamp: March 29, 2025, 05:26:02 pm
content: Quote from: coppercone2 on March 29, 2025, 04:12:53 pmNo, this was a discrete TCXO in a frequency counter, which cost an extra $100 on a $400 dollar counter.There are ceramic disc capacitors available with specific non-zero temperature coefficients for temperature compensating high frequency circuits. Combined with a fixed capacitance, trimming the temperature compensating capacitor allows trimming the total temperature coefficient of capacitance. A separate zero TC trimmer is then used to adjust the frequency.Today inexpensive TCXO modules are available, but in the past they were a very expensive option, so a discrete TCXO circuit could be economical even with the expense of trimming the temperature coefficient.

author: TimFox
author_rank: Super Contributor
timestamp: March 29, 2025, 05:38:58 pm
content: In the days of vacuum-tube communication receivers, oscillator tempco trimming could be done with a differential variable capacitor (one side increased while the other decreased with shaft rotation) and two fixed capacitors (one NP0 and the other with negative tempco). N220, N750, etc. dielectrics are Class I with good loss. Inductors tend to have positive tempco.

author: Xena E
author_rank: Frequent Contributor
timestamp: March 29, 2025, 06:26:59 pm
content: Quote from: David Hess on March 28, 2025, 10:41:34 amYes.IMC by cutting a slot with a diamond wheel, sealing with denatured bees wax.

author: coppercone2
author_rank: Super Contributor
timestamp: March 29, 2025, 09:55:21 pm
content: my idea was to scrape off the plating instead of trying to cut into the substrate. I am contemplating buying a diamond scribe tool to try itperhaps its as simple as drawing a smiley face on the capacitor with a scribe, or maybe drill holes in it and seal with bees waxI have that silly little pen drill, I wanted to buy diamond drill bits for it. I wonder if it would work as a good modification tool, by making divets in itI am also curious what drilling holes in a MOV might do

author: jonpaul
author_rank: Super Contributor
timestamp: March 30, 2025, 12:07:08 pm
content: get an easily avail piston or rotary trimcap variablej

author: TimFox
author_rank: Super Contributor
timestamp: March 30, 2025, 02:44:28 pm
content: I like pistons: really highQ.

author: David Hess
author_rank: Super Contributor
timestamp: March 30, 2025, 06:04:25 pm
content: Quote from: TimFox on March 30, 2025, 02:44:28 pmPiston trimmers are amazing.

author: TimFox
author_rank: Super Contributor
timestamp: March 30, 2025, 06:20:34 pm
content: New piston trimmers are pricey, but Surplus Sales of Nebraska has a good stock:https://www.surplussales.com/categories/1679-piston-trimmer-capacitors-index/

author: coppercone2
author_rank: Super Contributor
timestamp: March 30, 2025, 07:33:04 pm
content: you won't be putting that chassis assembly into a differential probe