EMRFD Message Archive 4793

Message Date From Subject
4793 2010-07-11 11:30:50 Robert Cerreto Need A varactor
Hey Guys,

I need either a BB109G or a BB139. I can not seem to find anyone who sells them. Would anybody in the group know where I can find them? Better yet, is there a more common substitute?

Thanks for helping
Bob WA!FXT





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4794 2010-07-11 12:37:30 Paul Daulton Re: Need A varactor
In lieu of a varactor try using a red led. I used two red leds in parallel (from radio shack) in place of a 30pf MV109 in a project recently with good results.

Look at Hans Summers site for an article on his experiments with red leds as varicaps. www.hanssummers.com

Good luck
Paul Daulton k5wms
----- Original Message -----
4795 2010-07-11 15:18:45 Tayloe Dan-P26412 Re: Need A varactor
I have used 1N4007s as varactors as well. The main problem that I have
found is not these devices (including LEDs) cannot be used as varactors,
it is just that since this is not their main purpose, the varactor
characteristics can vary significantly from device to device. Thus, it
is a bit different to try to use these in something like a club kit.

If you go to Mouser and look up "Varactor Diode", there are some that
are available that you might be able to user, but they are rather tiny
surface mounted stuff. They can be used as replacement to leaded parts
on PC board (such as bridging from a PCB pad to ground, but may need to
clean off a spot of the ground to bridge to) and are readily useful in
deadbug or "island" type construction.

The normal varactor diodes that we used to take for granted I think may
have fallen victim of the change over to lead free parts.

- Dan, N7VE

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4796 2010-07-11 15:44:54 Harold Smith Re: Need A varactor
Another possibility for a varactor substitute is the ordinary bipolar
transistor. Using the C-B junction as a varactor used to be fairly common
before varactors became widely available and inexpensive, and often the
datasheet will have a curve for capacitance vs voltage at that junction.
Look, for instance, at the ON Semiconductor datasheet for the MPS-A05
family. It has curves for both C-B (Cobo) and E-B (Cibo) capacitance vs.
reverse voltage.

Hope this helps.

de KE6TI, Harold


4797 2010-07-11 16:10:15 Stephen Wandling Re: Need A varactor
Scott Lowe sells MVAM108 and MVAM109 varactors at:
http://www.angelfire.com/electronic2/index1/

He has lots of other interesting stuff there as well, and has always
been very pleasant to deal with.

72
Stephen
VE7NSD

Robert Cerreto wrote:
> Hey Guys,
>
> I need either a BB109G or a BB139. I can not seem to find anyone who sells them. Would anybody in the group know where I can find them? Better yet, is there a more common substitute?
>
> Thanks for helping
> Bob WA!FXT
>
>
>
>
>
> [Non-text portions of this message have been removed]
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
>
>
4798 2010-07-12 00:07:04 Mike G3TGD Re: Need A varactor
Hi Bob

Mode Components in the UK (/www.modecomponents.co.uk) lists around 15
varactor types including the BB139 @ 30p.

best regards

Mike G3TGD

On 11 July 2010 19:30, Robert Cerreto <wa1fxt@yahoo.com> wrote:

>
>
> Hey Guys,
>
> I need either a BB109G or a BB139. I can not seem to find anyone who sells
> them. Would anybody in the group know where I can find them? Better yet, is
> there a more common substitute?
>
> Thanks for helping
> Bob WA!FXT
>
> [Non-text portions of this message have been removed]
>
>
>


[Non-text portions of this message have been removed]
4799 2010-07-12 07:11:03 Tim Re: Need A varactor
The MV209, BB109, etc. used to be a common item until a year or two ago.

The BB109 was a Thomson part from the mid-70's and seemed to be quite comm
4800 2010-07-12 07:48:38 davidpnewkirk Re: Need A varactor
4801 2010-07-12 07:59:50 Tom Need A varactor
Try www.kitsandparts.com <http://www.kitsandparts.com/> they have MVAM109's
MV209's and MV2105G's.

I've also ordered varactors and other parts from Elecraft before. They are
very reasonable both price and shipping wise for parts hard to get
elsewhere. Check their online schematics for part numbers. They are on the
west coast however, and Parts and Kits are on the east coast - faster and
cheaper.



Tom, ak2b



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4802 2010-07-12 08:32:51 ajparent1 Re: Need A varactor
4803 2010-07-12 09:37:56 Andy Re: Need A varactor
> I personally would HIGHLY ENCOURAGE that ham designers not only call out the varactor part numbers they use, but also call out the expected capacitance range over what voltage range for people who want to build it in the future.

I'm glad someone brought that up.

Every diode is also a varactor. Every diode.

One of the main characteristics that makes an actual "varactor"
unique, i.e., one that's made to be a varactor, is the gradation of
the impurities around the junction, to tailor the C vs. V curve,
and/or the F vs. V curve where F varies as C^-0.5.

By default, if you stick N and P materials together, the C/V curve is
not linear, and F/V sure isn't; plus it's not good for a very wide
range of capacitance or tuning frequency.

Some of the varactors talked about were created (using ion implant
techniques, I think) specifically to provide very wide tuning ranges
(>3:1 in frequency, to tune the entire AM broadcast band); or to make
the tuning linear so that the VCO gain stays constant, which matters
if it goes into a wide range PLL. I'd go with one of those special
varactors IF that particular characteristic is important to you; but
might not otherwise.

> Keeping photons off one's circuit's diode(s) to avoid misoperation isn't an issue of interest only to digital designers.

I learned about that many years ago when I used a pair of back to back
diodes for voltage limiting in a low frequency amp (I think it was
part of the loop filter for a PLL). It behaved strangely on the bench
when I pulled up a fluorescent lamp for a better view.

I think I replaced them with a couple of JFETs in black epoxy cases.
(Why JFETs? The gate-channel junction made a good enough diode. For
some strange reason they were the only cheap devices I found that were
insensitive to light. Truly opaque epoxy?)

Regards,
Andy
4804 2010-07-12 10:58:09 Tim Re: Need A varactor
4805 2010-07-12 21:13:56 n5emqrp Re: Need A varactor