Trimmer capacitor source

Thread Starter

upand_at_them

Joined May 15, 2010
940
Wow, that's a good deal. Do you know if that type is suitable for RF? Some of the circuits I want to build specify "ceramic trimmer", which I'm not sure those plastic encased ones are?
 

SamR

Joined Mar 19, 2019
4,492
Being from china and AliX they are strictly for experimental purposes and may not even be on specification. I tend to test almost everything I get from AliX and ask for a refund if it is more than ±20% (unless otherwise specified) out of range specification. For a ceramic check on DigiKey in the US or Arrow. Any of the major parts houses. AliX also has some good deals on inductors for playing around with. @Audioguru again where did you get the trimmer caps?
 

k1ng 1337

Joined Sep 11, 2020
701
Wow, that's a good deal. Do you know if that type is suitable for RF? Some of the circuits I want to build specify "ceramic trimmer", which I'm not sure those plastic encased ones are?
I believe the ones Sam posted are ceramic. I purchased a big pack like that and many didn't work or would only turn so many times before being damaged. If your making radios spend a little extra for a high quality trimmer because these little ones are a pain.
 

SamR

Joined Mar 19, 2019
4,492
I believe the ones Sam posted are ceramic
Nope, definitely plastic! Not for a power circuit! And NO SPECIFICATIONS or PDF! Strictly for playing around with at home. Not a bad little kit to have stuck away to play around with filters.
 

Audioguru again

Joined Oct 21, 2019
5,427
I got my tiny trimmer capacitors at a local electronic parts store that is gone now.
CAUTION. My FM transmitter has a high output power that will jam radio stations for neighbors. Then they might get the RF cops to confiscate the transmitter and maybe fine and/or jail you.
 

k1ng 1337

Joined Sep 11, 2020
701
Nope, definitely plastic! Not for a power circuit! And NO SPECIFICATIONS or PDF! Strictly for playing around with at home. Not a bad little kit to have stuck away to play around with filters.
Hmm maybe mine are plastic.. they were marketed as ceramic and now you guessed it no more listing!

I'll also add if you don't have a capacitance meter then your driving blind with such low values. You could try making one out of foil which worked well for me. It will easily couple to your body which makes tuning a mess.
 

SamR

Joined Mar 19, 2019
4,492
They were all ceramic until they "invented" injection moldable plastic. They might all be plastic now? When you start messing around with RLC circuits it is nice to invest in a good LCR meter although the cheap chinesium "do all" tester will at least get you into the ballpark if not right on home plate. Less than 20 pico takes a very good meter.
 
Last edited:

k1ng 1337

Joined Sep 11, 2020
701
They were all ceramic until they "invented" injection moldable plastic. They might all be plastic now? When you start messing around with RLC circuits it is nice to invest in a good LCR meter although the cheap chinesium "do all" tester will at least get you into the ballpark if not right on home plate. Less than 20 pico takes a very good meter.
Any reason not to opt for a homemade foil capacitor?
 

Thread Starter

upand_at_them

Joined May 15, 2010
940
Will those plastic ones behave the same as the [supposedly ceramic] ones that Audioguru used in the above circuit? Is capacitance the only important characteristic?...Or will they behave differently.

Yeah, I *should* buy quality ones, but I want a bunch of them and don't want to break the bank.
 

k1ng 1337

Joined Sep 11, 2020
701
I made one with a piece of 8 1/2 x 11 paper as insulator with two pieces of foil the same size. Worked ok as long as it isn't bumped. You could also try long pieces of wire as plates for some interesting synthesizer effects.

I've tuned by moving my hand near a wire as well.
 

SamR

Joined Mar 19, 2019
4,492
I've tuned by moving my hand near a wire as well.
That's the main problem trying to measure picofarads even after zeroing the relative reference. You can zero out the wiring connections but your body's movement can skew the reading unless you distance yourself. Also, tweaking an adjustable trimmer cap has the same problems. One reason why Farraday cages are used for RF. Not just to prevent RF from escaping but also to prevent outside sources from interfering.
 
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