Variable capacitor of the range 0-5pF is available?

 

hi CC,
Check here.
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https://www.google.com/search?clien...HXQZCzAQjJkEegQIDBAC&biw=1172&bih=637&dpr=1.4

 

I have used these when I needed something to trim VHF oscillators.

https://en.wikipedia.org/wiki/Gimmick_capacitor

 

Variable capacitor of the range 0-5pF is available?

I doubt it - how would it achieve zero capacitance?

 

I doubt it - how would it achieve zero capacitance?

 

In the pic. attached; why there is coax cable braid connection from capacitor plates to jumper ?Is this for reducing the capacitance value? I saw this in some old circuits, is this necessary for today's applications?

 

In the pic. attached; why there is coax cable braid connection from capacitor plates to jumper ?Is this for reducing the capacitance value? I saw this in some old circuits, is this necessary for today's applications?

It's low reactance braided (also flexible) ground connection to an RF ground. Yes, a proper RF ground is necessary for today's applications, EM hasn't changed from then to now but the size of typical RF components has.
https://www.awcwire.com/allied-university/this-vs-that/round-vs-flat-wire-braid

 

It's low reactance braided (also flexible) ground connection to an RF ground. Yes, a proper RF ground is necessary for today's applications, EM hasn't changed from then to now but the sized of typical RF components has.
https://www.awcwire.com/allied-university/this-vs-that/round-vs-flat-wire-braid

Thank you so much!

 

This is an old variable capacitor from ASP(in the body it is written like that),I searched a lot for this kind but bad luck didn't find any. Rating is 0.5 to 5pf also doubted the isolated white shaft. Why there is an isolated shaft like this?

 

This is an old variable capacitor from ASP(in the body it is written like that),I searched a lot for this kind but bad luck didn't find any. Rating is 0.5 to 5pf also doubted the isolated white shaft. Why there is an isolated shaft like this?

https://www.rfparts.com/capacitors.html

 

https://www.rfparts.com/capacitors.html

 

https://www.surplussales.com/VARIABLES/VARIABLETRIMMERS/VARTRIMM5.HTML

Good luck finding an exact replacement.

 

The white stuff is ceramic, in this case probably a low dielectric constant ceramic.

You might find this interesting: http://sm0vpo.altervista.org/use/tuning_caps2.htm

 

The white stuff is ceramic, in this case probably a low dielectric constant ceramic.

You might find this interesting: http://sm0vpo.altervista.org/use/tuning_caps2.htm

Is this a customized one? I didn't find any like this in Google! what's the need of that ceramic? Is that necessary for low pf range? Sorry to ask you a lot questions!
Thanks!

 

Youwill not have any success with google. Why are you seeking another capacitor like this?

 

Youwill not have any success with google. Why are you seeking another capacitor like this?

replacement!

 

OK,Isee nothing wrong with the one in the photo, but it may just be a sample. Aside from capacitance,the voltage rating, which is determined by the plate spacing, is the other critical variable. One place that might have them is "RF Parts", another place that sells surplus is "Fair Radio", which has an on-line catalog. And in addition, some equipment contains capacitors that could be removed and used. But it is not likely that you will find a variable capacitor with that braided cable attached.

 

OK,Isee nothing wrong with the one in the photo, but it may just be a sample. Aside from capacitance,the voltage rating, which is determined by the plate spacing, is the other critical variable. One place that might have them is "RF Parts", another place that sells surplus is "Fair Radio", which has an on-line catalog. And in addition, some equipment contains capacitors that could be removed and used. But it is not likely that you will find a variable capacitor with that braided cable attached.

Thank you so much! I want to chk with "Fair Radio"

 

Is this a customized one? I didn't find any like this in Google! what's the need of that ceramic? Is that necessary for low pf range? Sorry to ask you a lot questions!
Thanks!

I do. It know whether this capacitor is customized or not.

The ceramic (“white stuff”) provides the basic structure for the capacitor. These days plastic is used a lot more than ceramic.

By the way, decades ago, when I enjoyed radio as a hobby and these open frame type (my name for it) variable capacitors we’re readily available I sometimes reduced the capacitance by pulling some of the rotating plates off of the shaft.

By the way, low variable capacitance values like this are often achieved with Varactor Diodes these days.

https://en.m.wikipedia.org/wiki/Varicap

 

The ceramic base of the capacitor is certainly needed for mechanical stability, and it does not show any hint of being modified except for the lead soldered on.There may be some issues with corrosion, though.
A "varicap diode" would be a poor substitute because it requires a bias voltage to set the effective capacitance, which is totally a different mode from providing a very low-loss stable capacitance.