Need to find an old variable capacitor

In summary, the individual needed help finding old radio components for building a radio circuit and eventually found them online. The conversation then shifted to discussing the use of variable capacitors and the suggestion to learn about varicap technology. It was also mentioned that searching for vintage radios or spare parts could be helpful in finding components. Ultimately, the person was able to solve their problem and expressed gratitude to those who offered assistance.
  • #1
michael1978
434
19
hello
i buy allmost all thing needed, for buil you own radio circuits 2013,
but in electronics shop he told me , there are old, you can find it only in old radio
he can't help, those components don't sell anymore,

maybe somebody can help me how to find online those component

VC1: two-gang variable capacitor: 140pF, 60F = 2
VC1: 140pF RF and 60pF oscillator = 2
VC1: variable capacitor twin gang 270pF and 270pF = 2
VCI: TWO SECTION VARIABLE CAPACITOR 140pF ,60pF = 2
 
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  • #2
michael1978 said:
hello
i buy allmost all thing needed, for buil you own radio circuits 2013,
but in electronics shop he told me , there are old, you can find it only in old radio
he can't help, those components don't sell anymore,

maybe somebody can help me how to find online those component

VC1: two-gang variable capacitor: 140pF, 60F = 2
VC1: 140pF RF and 60pF oscillator = 2
VC1: variable capacitor twin gang 270pF and 270pF = 2
VCI: TWO SECTION VARIABLE CAPACITOR 140pF ,60pF = 2
If you haven't been able to find the values you need in the dual-gang configuration, have you considered getting a dual-gang capacitor that can be taken apart so you can modify it to the values you need?

https://upload.wikimedia.org/wikipe...le_Capacitor.jpg/220px-Variable_Capacitor.jpg
220px-Variable_Capacitor.jpg
 

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  • #6
michael1978 said:
Sorry, but i don't see any variable capacitor in that page
That's weird. That's what that whole selection of dual-ganged capacitors is all about!

What do you see at the link?
 
  • #7
berkeman said:
That's weird. That's what that whole selection of dual-ganged capacitors is all about!

What do you see at the link?
sorry don't misonderstand me, i don't know about those variable i know just capactior and trimmers
have a nice wekend.
 
  • #9
michael1978 said:
sorry don't misonderstand me, i don't know about those variable i know just capactior and trimmers
have a nice wekend.

you asked about variable capacitors

you were shown whereto get them and what sort of prices they will cost
what didn't you understand ?Dave
 
  • #10
Fwiw the google shopping link returns no hits for me (as in google couldn't find anything).
 
  • #11
michael1978 said:
Sorry, but i don't see any variable capacitor in that page
Lord Crc said:
Fwiw the google shopping link returns no hits for me (as in google couldn't find anything).
Interesting. I wonder if the search is personalized to me or something. Anyway, just type what I did in the search bar and click on Shopping links. You should get what I see...

dual-gang potentiometer search.jpg
 

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  • #12
I get exactly the same page
 
  • #13
Lord Crc said:
Fwiw the google shopping link returns no hits for me (as in google couldn't find anything).
Do you mean you clicked on the link provided and didn't see any or do you mean you did your own search and didn't get any?
 
  • #14
hello thanks to everybody... i solved i found,
but now i am trying to learn varicap

thnxxxxxxxxxxxxxx
 
  • #15
@michael1978 Did you try eBay? There are many variable capacitors for sale (vintage, mostly). You just need to sort through the ads and contact sellers to see if they have the values you need.
When you are searching for an item, you need to take time and spread your net wide. Why not also look for a vintage radio advertised 'for spares'?
 
  • #16
sophiecentaur said:
@michael1978 Did you try eBay? There are many variable capacitors for sale (vintage, mostly). You just need to sort through the ads and contact sellers to see if they have the values you need.
When you are searching for an item, you need to take time and spread your net wide. Why not also look for a vintage radio advertised 'for spares'?
thank you very much, i solved, but the man in electronics shop he told try to learn varicap, because they are not in use any more.
greetings.
 
  • #17
michael1978 said:
thank you very much, i solved, but the man in electronics shop he told try to learn varicap, because they are not in use any more.
greetings.
That's his opinion but varicap is a different technology. It all depends what you want to achieve. Starting with a very basic receiver would give you a chance to actually understanding about receivers. There is so much 'hidden' inside modern electronic components. The air spaced variable C is one of the few components that is totally open to view. You can also see all the structures in a simple thermionic valve - but that may be too much trouble to learn about.
 
  • #18
This is making me (age 77) all nostalgic! So boring nowadays with transistors replacing those beautiful glowing vacuum tubes, and air-gap dual or 3-gang variable air capacitors rotating merrily back & forth compared to lifeless varactors! I guess all that remains is the antenna loop & speaker - or did the voice-coil speaker also bite the dust?

With tears welling up in my eyes I think of the beautiful Zenith AM radio I bought used in 1958 with a tuned rf stage (3-section variable capacitor!) Dependably picked up a Mexican-based english-speaking station in Boston! I ruined it trying to convert it to short-wave. Follies of youth! I could kill myself even now thinking about that beautiful Zenith. :H Nearly bought one like it on ebay even though I'd never listen to it. Might still look for one again someday.
 
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  • #19
berkeman said:
That's weird. That's what that whole selection of dual-ganged capacitors is all about!

What do you see at the link?
I see this:
cap.png
 

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  • #20
darth boozer said:
I see this
Weird!
 
  • #21
michael1978 said:
hello
i buy allmost all thing needed, for buil you own radio circuits 2013,
but in electronics shop he told me , there are old, you can find it only in old radio
he can't help, those components don't sell anymore,

maybe somebody can help me how to find online those component

VC1: two-gang variable capacitor: 140pF, 60F = 2
VC1: 140pF RF and 60pF oscillator = 2
VC1: variable capacitor twin gang 270pF and 270pF = 2
VCI: TWO SECTION VARIABLE CAPACITOR 140pF ,60pF = 2

https://www.google.com/search?q=var...nmKTZAhURtlMKHU8KCyEQsAQImwE&biw=1594&bih=848

https://www.aliexpress.com/item/Fud...f7d0OBM8D5Cbtcy14wt1aheCjEf0-WtxoC_T8QAvD_BwE

http://www.surplussales.com/variables/airvariables/AirVar2.html
 
  • #22
Many old amateur radios were coil-tuned, without any variable cap, like this (note the regeneration):
mrb465_30-500x322.gif

The "L1" inductor is rotating inside the "L2" like this:
image?id=849510600454&t=0&plc=WEB&tkn=*4ubipGS3FeMb-4oaChV1igZrk3A.jpg

- to me, it's even more fun than a variable capacitor . . .
There is a big advantage: You can connect the outdoor antenna via a long coaxial cable, thus avoiding the indoor electromagnetic noises. The cable capacitance then participates in the input LC without reducing the tuning range.
 

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  • #23
AlexCaledin said:
Many old amateur radios were coil-tuned, without any variable cap, like this (note the regeneration):
View attachment 220290
The "L1" inductor is rotating inside the "L2" like this:
View attachment 220291
- to me, it's even more fun than a variable capacitor . . .
There is a big advantage: You can connect the outdoor antenna via a long coaxial cable, thus avoiding the indoor electromagnetic noises. The cable capacitance then simply works as the input LC capacitance without reducing the tuning range.
Pretty, in fact mind-blowing, but perhaps a bit unwieldy for a table-top radio :smile: . Did or would this kind of tuning work at 550-1600 KHz and without an external antenna?
 
  • #24
rude man said:
would this ... work at 550-1600 KHz?

Yes that circuit was exactly for those frequencies, when without the C2.
. . .
But the tuning coils themselves did not work as antenna, they typically were placed inside the metal box:
odnolampovyi_dvuhkaskadnyi_priemnik_2.jpg
 

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  • #25
berkeman said:
Interesting. I wonder if the search is personalized to me or something. Anyway, just type what I did in the search bar and click on Shopping links. You should get what I see...

Seems to be Google Shopping issue on Firefox Mobile. Works in Chrome and Firefox on my desktop computer. Searching for other things returns many hits on FF mobile tho... weird.
 
  • #26
berkeman said:
Weird!
Only a bit "weird" when you consider how these search engines work. They index (god knows how) all the terms of the page and use the index to give you hits. If the original page has been modified in some way (very possible if someone plays about with a components catalogue without publishing the fact that it's been changed, then Google or other search engine will send you to the original location. Idiot site managers who don't take that into account will shoot themselves in the foot. :wink:
 
  • #27
AlexCaledin said:
Many old amateur radios were coil-tuned, without any variable cap, ...
A rotary variable coupler or transformer is called a "variometer". It can be used as a variable inductor by connecting the two coils in series. It can then give a very high ratio of maximum to minimum inductance. Variable capacitors cannot achieve such high ratios.
https://en.wikipedia.org/wiki/Transformer_types#Variometer_and_variocoupler
 
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  • #28
The following have trimmer caps that you set so that you get the proper range from the variable parts:
https://www.ebay.com/itm/TWO-PCS-VARIABLE-tuning-PV-capacitor-AM-transistor-radio-2-section-cap-w-KNOB-/292392042039
 
  • #29
thnx to everybody, man that is so big, i did not know, i think better to learn varicap, have a nice wekend to everybody
 
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  • #30
You can usually remove plates from an old variable capacitor to make a lower value capacitance.

Varicaps will work but the high capacitance needed for use on the BC band are now rare. Low voltage rectifier diodes, such as 1N4001, often met the specifications. The area of the diode is what makes the difference, so older designs have higher capacitance. The best I found were big diodes from old automotive alternators. These days I might investigate power mosfets as they have high capacitance between the gate and source. Tie the source and drain together.

One problem with varicaps is cancellation of the distortion in oscillators, or when big signals are present. Distortion is best reduced by using opposed matched pairs of diodes as shown here.
https://en.wikipedia.org/wiki/Varicap#Tuning_circuits
 
  • #31
Baluncore said:
You can usually remove plates from an old variable capacitor to make a lower value capacitance.

Varicaps will work but the high capacitance needed for use on the BC band are now rare. Low voltage rectifier diodes, such as 1N4001, often met the specifications. The area of the diode is what makes the difference, so older designs have higher capacitance. The best I found were big diodes from old automotive alternators. These days I might investigate power mosfets as they have high capacitance between the gate and source. Tie the source and drain together.

One problem with varicaps is cancellation of the distortion in oscillators, or when big signals are present. Distortion is best reduced by using opposed matched pairs of diodes as shown here.
https://en.wikipedia.org/wiki/Varicap#Tuning_circuits
thak you, but strange i don't find tutorial about varicap.
 
  • #33
Baluncore said:
thank you i read all, but i still don't know how to measure varicap, i know how to bias, but can you show me one example how to measure maximum picoFarad
and i read in google resistor isulation, somewhere say 10K to 47K, some several mega ohms, i don't understand.
 
  • #34
michael1978 said:
i still don't know how to measure varicap,
Measuring small values of Capacitance is quite difficult. You can use a "Capacitance Bridge", which is probably regarded as old fashioned. You can resonate with a known Inductance and the C can be deduced. But small Capacitances are dogged with other stray capacitances and it requires a fair bit of experimental skill to get a reliable value. Someone may well post another more modern method but I'd bet the equipment would cost you a bit!
 
  • #35
michael1978 said:
and i read in google resistor isulation, somewhere say 10K to 47K, some several mega ohms, i don't understand.
No DC current flows, only leakage, so a high R can set the diode DC bias voltage while not over-loading the AC resonant circuit.

A varactor can be any diode that is slightly reverse biassed. All diodes have changing capacitance in that region of operation, so if that changing capacitance is used, it is a varactor in that circuit.

Best results are with small signals since the biggest change in capacitance occurs close to the point where the varactor will start to conduct and so rectify the signal and start to pump charge and set it's own bias.

To measure the capacitance you can make a tuned circuit with a low amplitude signal or oscillation and measure the frequency. You might start investigating with a simple oscillator and a pair of power diodes, using between 2 and 10 volts of reverse bias. The change will be small at such high reverse bias voltages but the signal will not affect the bias. Use smaller signals and lower reverse bias as you progress.

You might build a crystal set receiver with any variable mechanical capacitor, then replace the mechanical tuning cap with a pair of power diodes and a bias network controlled by a potentiometer.
 
<h2>1. Where can I find an old variable capacitor?</h2><p>Old variable capacitors can often be found at electronic surplus stores, online marketplaces such as eBay, or through online communities and forums dedicated to vintage electronics.</p><h2>2. What is the best way to determine the value of an old variable capacitor?</h2><p>The value of an old variable capacitor can be determined by looking at the markings on the capacitor itself or by using a multimeter to measure its capacitance. It is important to note that the value may have changed over time due to aging or damage.</p><h2>3. How do I know if an old variable capacitor is still functional?</h2><p>To determine if an old variable capacitor is still functional, you can use a multimeter to measure its capacitance. If the measured value is within the expected range, it is likely still functional. Additionally, visually inspecting the capacitor for any physical damage or corrosion can also help determine its functionality.</p><h2>4. Can I use a modern variable capacitor as a replacement for an old one?</h2><p>In some cases, a modern variable capacitor may be able to be used as a replacement for an old one. However, it is important to ensure that the values and specifications of the modern capacitor match those of the old one to ensure proper functionality. It may also be necessary to make adjustments to the circuit in order to accommodate the modern capacitor.</p><h2>5. Are there any alternatives to using an old variable capacitor?</h2><p>Depending on the specific application, there may be alternative components that can be used in place of an old variable capacitor. These could include fixed capacitors, trimmer capacitors, or even digital variable capacitors. It is important to consult with a knowledgeable individual or do thorough research to determine the best alternative for your specific needs.</p>

1. Where can I find an old variable capacitor?

Old variable capacitors can often be found at electronic surplus stores, online marketplaces such as eBay, or through online communities and forums dedicated to vintage electronics.

2. What is the best way to determine the value of an old variable capacitor?

The value of an old variable capacitor can be determined by looking at the markings on the capacitor itself or by using a multimeter to measure its capacitance. It is important to note that the value may have changed over time due to aging or damage.

3. How do I know if an old variable capacitor is still functional?

To determine if an old variable capacitor is still functional, you can use a multimeter to measure its capacitance. If the measured value is within the expected range, it is likely still functional. Additionally, visually inspecting the capacitor for any physical damage or corrosion can also help determine its functionality.

4. Can I use a modern variable capacitor as a replacement for an old one?

In some cases, a modern variable capacitor may be able to be used as a replacement for an old one. However, it is important to ensure that the values and specifications of the modern capacitor match those of the old one to ensure proper functionality. It may also be necessary to make adjustments to the circuit in order to accommodate the modern capacitor.

5. Are there any alternatives to using an old variable capacitor?

Depending on the specific application, there may be alternative components that can be used in place of an old variable capacitor. These could include fixed capacitors, trimmer capacitors, or even digital variable capacitors. It is important to consult with a knowledgeable individual or do thorough research to determine the best alternative for your specific needs.

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