Need to find an old variable capacitor

[michael1978]

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

 

[berkeman]

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

 

[michael1978]

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
View attachment 220027

So you do any value, but where can you buy

 

[berkeman]

So you do any value, but where can you buy

https://www.google.com/search?q=dua...DipJnZAhUOEawKHW3ECQkQsxgIKA&biw=1033&bih=671

 

[michael1978]

https://www.google.com/search?q=dua...DipJnZAhUOEawKHW3ECQkQsxgIKA&biw=1033&bih=671

Sorry, but i don't see any variable capacitor in that page

 

[berkeman]

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?

 

[michael1978]

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.

 

[davenn]

https://www.google.com/search?q=dua...DipJnZAhUOEawKHW3ECQkQsxgIKA&biw=1033&bih=671

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?

@berkeman there was nothing wrong with your link, it showed lots of variable caps Dave

 

[davenn]

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

 

[Lord Crc]

Fwiw the google shopping link returns no hits for me (as in google couldn't find anything).

 

[berkeman]

Sorry, but i don't see any variable capacitor in that page

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...

 

[phinds]

I get exactly the same page

 

[phinds]

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?

 

[michael1978]

hello thanks to everybody... i solved i found,
but now i am trying to learn varicap

thnxxxxxxxxxxxxxx

 

[sophiecentaur]

@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'?

 

[michael1978]

@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.

 

[sophiecentaur]

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.

 

[rude man]

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. Nearly bought one like it on ebay even though I'd never listen to it. Might still look for one again someday.

 

[darth boozer]

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:

 

[berkeman]

I see this

Weird!

 

[Brendan Graham]

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

 

[AlexCaledin]

Many old amateur radios were coil-tuned, without any variable cap, like this (note the regeneration):

The "L1" inductor is rotating inside the "L2" like this:

- 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.

 

[rude man]

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 . Did or would this kind of tuning work at 550-1600 KHz and without an external antenna?

 

[AlexCaledin]

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:

 

[Lord Crc]

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.

 

[sophiecentaur]

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.

 

[Baluncore]

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

 

[Mark Harder]

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

 

[michael1978]

thnx to everybody, man that is so big, i did not know, i think better to learn varicap, have a nice wekend to everybody

 

[Baluncore]

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

 

[michael1978]

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.

 

[Baluncore]

Varicap = Varactor.

http://www.radio-electronics.com/info/data/semicond/varactor-varicap-diodes/basics-tutorial.php

http://www.futureelectronics.com/en/diodes/tuning-varactor.aspx

http://www.physics-and-radio-electr...tordiode-construction-definition-working.html

 

[michael1978]

Varicap = Varactor.

http://www.radio-electronics.com/info/data/semicond/varactor-varicap-diodes/basics-tutorial.php

http://www.futureelectronics.com/en/diodes/tuning-varactor.aspx

http://www.physics-and-radio-electr...tordiode-construction-definition-working.html

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.

 

[sophiecentaur]

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!

 

[Baluncore]

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.

 

[berkeman]

Someone may well post another more modern method but I'd bet the equipment would cost you a bit!

Yep. This is how we do it in our lab. Use the bias voltage feature of the old HP 4194, and be sure to calibrate it beforehand if you want to be measuring small capacitance values...

http://www.geocities.jp/etm_llc/pub/Z_report/pic2/4194A_16047D.jpg

 

[sophiecentaur]

Ha ha. Like I said - it would cost a bit. hp equipment is nice stuff. It always used to impress me that different pieces of hp kit would actually agree with each other. I always reckoned that there was some sub-ether comms between all hp instruments so that they could all get their stories to agree.
For home measurement, the best that most of us can hope for is a socket on a DMM for component measurement. Near enough for Jazz mainly.

 

[sophiecentaur]

@michael1978 I notice that you are double posting about this varicap measurement question. The Mods may complain about that. Best to keep things together or people can miss the conversation.
Also I think we are getting a bit astray from the original question. Your friendly man in the electronics shop was really not helping you when he suggested using a diode instead of an air spaced variable C. They are used for entirely different purposes.
You want to make an old fashioned AM receiver then make one. It is probably within your capabilities but trying to re-design the tuning stage to include a different technology is certainly not going to work for you. You need a result out of this and not just frustration. I know. I have been in the same position.

 

[berkeman]

Ha ha. Like I said - it would cost a bit. hp equipment is nice stuff.

Well if you or the OP ever make it across the Pond and visit Silicon Valley, ping me and you'll get a tour of the HW Lab and you can measure anything you want with our equipment.

 

[sophiecentaur]

Well if you or the OP ever make it across the Pond and visit Silicon Valley, ping me and you'll get a tour of the HW Lab and you can measure anything you want with our equipment.

That would be nice. I will be visiting my son in Queens (NY) this year some time but it's still a bit of a way to go to California. I will need to present a convincing case to my dear lady wife.

 

[michael1978]

Yep. This is how we do it in our lab. Use the bias voltage feature of the old HP 4194, and be sure to calibrate it beforehand if you want to be measuring small capacitance values...

http://www.geocities.jp/etm_llc/pub/Z_report/pic2/4194A_16047D.jpg
View attachment 220573

thnx, i want just to know the maximum capacitance, where to read of to take information

 

[michael1978]

@michael1978 I notice that you are double posting about this varicap measurement question. The Mods may complain about that. Best to keep things together or people can miss the conversation.
Also I think we are getting a bit astray from the original question. Your friendly man in the electronics shop was really not helping you when he suggested using a diode instead of an air spaced variable C. They are used for entirely different purposes.
You want to make an old fashioned AM receiver then make one. It is probably within your capabilities but trying to re-design the tuning stage to include a different technology is certainly not going to work for you. You need a result out of this and not just frustration. I know. I have been in the same position.

I don't know what to think about him, he look very good man

 

[michael1978]

Well if you or the OP ever make it across the Pond and visit Silicon Valley, ping me and you'll get a tour of the HW Lab and you can measure anything you want with our equipment.

i think he cost to much of not?

 

[sophiecentaur]

I don't know what to think about him, he look very good man

He may be a good man but he runs a shop and wants to sell things.
Also, he may not be used to teaching. Rule number one about helping people is not to present them with an ever widening field of knowledge when it's not necessary. You now have extra worry about the details of varactor diodes, You do not need this worry - you need an old fashioned air-spaced mechanical capacitor. They are available from various sources and you just need to keep looking on the 'fringe market'. The actual value and range may not be very important and you do not need exactly the same capacitor as the one on the diagram you are using. Take some time with your search. Good luck.

 

[michael1978]

He may be a good man but he runs a shop and wants to sell things.
Also, he may not be used to teaching. Rule number one about helping people is not to present them with an ever widening field of knowledge when it's not necessary. You now have extra worry about the details of varactor diodes, You do not need this worry - you need an old fashioned air-spaced mechanical capacitor. They are available from various sources and you just need to keep looking on the 'fringe market'. The actual value and range may not be very important and you do not need exactly the same capacitor as the one on the diagram you are using. Take some time with your search. Good luck.

hey man he told me that they are not in use al long, and he don't know where to find it, now only varicap they use in place van variable capacitor

 

[sophiecentaur]

hey man he told me that they are not in use al long, and he don't know where to find it, now only varicap they use in place van variable capacitor

He's right when he says they are not in commercial use and he couldn't sell you one but he was wrong to say they cannot be obtained. He did not recognise your need to live a bit of history.
If you want to build a modern receiver then that would be possible, with Integrated circuits and semiconductor tuning capacitors but they are complex and you would not be getting the 'full experience'. Also, if it didn't work first time, you may not be able to sort out the problem. A very simple receiver could be much more practical for you to make - once you have located all the right components. I think we are all rooting for you about this!

 

[michael1978]

He's right when he says they are not in commercial use and he couldn't sell you one but he was wrong to say they cannot be obtained. He did not recognise your need to live a bit of history.
If you want to build a modern receiver then that would be possible, with Integrated circuits and semiconductor tuning capacitors but they are complex and you would not be getting the 'full experience'. Also, if it didn't work first time, you may not be able to sort out the problem. A very simple receiver could be much more practical for you to make - once you have located all the right components. I think we are all rooting for you about this!

thank you man i think i solved