Silver mica cap

[timmy]

Does it make a difference in the voltage of a mica capacitor in an rf vhf circuit.
A 68pf 50 or 100 volt mica but a 500 volt mica won’t work.

[Alex KL-1]

Originally Posted by timmy

Does it make a difference in the voltage of a mica capacitor in an rf vhf circuit.
A 68pf 50 or 100 volt mica but a 500 volt mica won’t work.

The 500V one is large (=inductance), or is very leaky?

[timmy]

Originally Posted by Alex KL-1

The 500V one is large (=inductance), or is very leaky?

So your opinion is the 500volt should work in place of a 50 or 100 volt

[Alex KL-1]

Originally Posted by timmy

So your opinion is the 500volt should work in place of a 50 or 100 volt

If it are not giant (cumbersome to apply), will work fine.
Of course, generally the ceramics are more indicated for the VHF work, due to lower self-inductance, and other properties, like temperature coefficient.

[timmy]

Does anyone know where to find 68pf 50 volt silver mica capacitors unless someone here has them.

[timmy]

Can a 1n34 detector diode be used in place of a to92 vhf Varicap diode. Even while checking in diode check both one way one has a higher number then the other. don’t know if this makes any difference.

[Alex KL-1]

The 1N34 are not too reliable for capacitance changing since it are constructed with a different juncion tech (ir more like like a Schottky-like; some metal-to-N type semi). Even a common silicon diode are more suitable here. But is a matter to discover it's code and find some compatible type.

[timmy]

Originally Posted by Alex KL-1

The 1N34 are not too reliable for capacitance changing since it are constructed with a different juncion tech (ir more like like a Schottky-like; some metal-to-N type semi). Even a common silicon diode are more suitable here. But is a matter to discover it's code and find some compatible type.

But it may work?

[Alex KL-1]

Perhaps it will kill the tuned circuit and not work (is there some risk). Depending how it is wired in the circuit. The low forward voltage of it will kill it if it works with low bias. And, will not be effective at action, being too resistive and killing the Q, or not varying the capacitance in the needed range.
I recommend a silicon diode here at least (the first varicap ones are simply some selected diodes from another application).

[bandersen]

LEDs work fairly well too

[timmy]

[QUOTE=bandersen;3259441]LEDs work fairly well too[/QUOT
LEDs but they are low voltage how would that work does color matter I’m lost

[bandersen]

How much voltage are you putting across it? Red seems to work best.
http://www.hanssummers.com/varicap/varicapled.html

Same guy trying rectifier diodes as varactors.
http://www.hanssummers.com/varicap/varicapdiode.html

[timmy]

Originally Posted by bandersen

How much voltage are you putting across it? Red seems to work best.
http://www.hanssummers.com/varicap/varicapled.html

Same guy trying rectifier diodes as varactors.
http://www.hanssummers.com/varicap/varicapdiode.html

I think it’s around 30-35 volts different ground options for this it may be 15 volts or maybe just use a to92 transistor with high enough voltage and cut the base pin off.

[timmy]

Does an adjustable pf capacitor go bad with age.

[old_tv_nut]

Originally Posted by timmy

Does an adjustable pf capacitor go bad with age.

Are you still talking about a varicap diode, or a capacitor you adjust with a screwdriver?