Where to find varactor diodes ?

[lordvader88]

Went to make a sweep oscillator then learned of diodes that change their capacitance vs. voltage.

Its possible I have some from stuff I've scrapped ? What old stuff uses them ? I don't want to wait months on ebay.

And is there other ways to achieve the same affect

[medical-nerd]

Hiya

Have a look at what this chap has done using different types of diodes as varicaps as a start.

http://www.hanssummers.com/varicap.html

Cheers

[firewalker]

Old analog tv tuners are full of varicap diodes.

Alexander.

[lordvader88]

thanks 1st poster, I shall proceed again


I have +3? of those from CRT TVs /VCRs ...hmmm, but in the meantime http://www.hanssummers.com/varicap/varicaporig.html, I'll make it and try common diodes/LEDs

[cdev]

I have bought them from vendors who sell parts to people who build stuff.. You can also find a lot of old parts on ebay.

Also, hansummers site will tell you - old LEDs and some other diodes sometimes make decent varactor diodes.

They can save money and space over variable capacitors in receiving applications.

[lordvader88]

I have a few old 1980s/90s diodes too

[BrianHG]

High voltage zener diodes work well, like 75v, 250mw.  Lower voltage zeners have higher capacitance and work well from 0.5v to around 50% below their rated voltage with a smooth curve.  I used to use a few 75v zd with the first 1-12v to make a voltage tuned FM radio & to tune crystals on an MCU port.

Also, look here:
https://www.digikey.ca/products/en/discrete-semiconductor-products/diodes-variable-capacitance-varicaps-varactors/282?k=tuning%20diodes

These below here are expensive, something like 3-9$ per diode...
There are silicon hyper-abrupt tuning diodes from motorola which will go from 300pf down to 10pf in 1 thru 10v.

Only AM radio Tuning diodes have that super wide capacitance sweep VS voltage, wider than Motorola's hyper-abrupt, within the first 10v.  Something like 600pf down to 15pf.  Philips/ECG - Now NXP - used to specialize in these and you find them in PLL tuned AM synthesizer radios.

[cdev]

Kitsandparts.com or

dans small parts and kits  may have them, otherwise, ebay.