I am working on building an ultrasound generator, I found the plans for one using relatively low amounts of parts, but it seems places that sell
electrical components are lacking these days.
I would harvest these parts from old electronics, but upon searching through my junk piles I am still missing a few.
741 op amp
2N3904 transistor
25 and 50K potentiometers
and several capacitors and resistors
If you needed such parts how/where would you find them?
Thanks,
-ssddtumadre - 22-4-2008 at 07:06
Computer monitors have a very wide assortment of parts.
If you want to get creative you could take the sweep generator out and couple it to a speaker.
You may not be able to find a 741, there are a lot of replacements for it, google can help with that.
I will let others recommend the 'best' companies, but i bet you can find all the parts you need from an old Tv etc. 100% of my electronics experience
came from the recycling center-jeffB - 22-4-2008 at 07:16
I know Radio Shack is a sad shadow of its former self, but they still carry parts like this. You probably wouldn't find a 25K pot, but I'll be you
could substitute a 50K and just be careful of the adjustment range, or cobble something up by paralleling a fixed resistor.
Back when I was tinkering with electronics, Jameco was my primary source for parts that I couldn't get from RS. Digikey has a wider selection, but
they were more oriented toward pros. I never bothered with Mouser or any of the other giants.
For that matter, IM me, and I could probably find my stash of 741s and 2N3904s (I bought a bag of 100 way back when). Might be able to help with the
resistors and caps, too. No guarantees of their condition after thirty years in a closet, but they don't really spoil. 12AX7 - 22-4-2008 at 07:46
Digikey, Mouser, etc.
741 has been obsolete for a number of years. Any bipolar op-amp will substitute, and FET amps (e.g., LF411, TL071, etc.) may also work. Art of
Electronics recommends LF411 for most generic op-amp uses.
I can't believe your junk doesn't have a 2N3904-ish transistor. Any generic Japanese transistor (like C1815, C945, etc.) will suffice (mind the
pinout differences).
Timssdd - 22-4-2008 at 07:49
Hmmmm... I think I have an old 5inch TV laying around that could be sacrificed. I'll have to take a gander inside (after discharging it of course) and
see what I can find.
Also, thanks -jeffB for the sites.
-ssddMagpie - 22-4-2008 at 09:46
I have limited experience in buying electronic parts, but here's my recommendations: To save freight & time buy local (ie, Radio Shack) if they
have what you want. For mail order I found Mouser best, then Newark, then Allied Electronics, Digikey, etc.IrC - 22-4-2008 at 12:03
All the places mentioned are high dollar, especially rat shack (which also has little to offer in the way of parts). Try Circuit Specialists or
Electronic Goldmine in the Phoenix area, for big surplus stuff (especially older, tube related, high voltage, and so on) try Fair Radio in Lima Ohio.
IIRC Goldmine even has those hard to find ultrasonic transducers. They all have websites you can google.
I forgot to add, All Electronics is another place you should check out.
[Edited on 4-22-2008 by IrC]Twospoons - 22-4-2008 at 14:10
BG micro is another online "surplus" supplier you should look at.
If you want something specific, I find it easiest to use Mouser, or Digikey - the prices aren't too bad (not the cheapest, but not the dearest
either), and the stock range is huge, and comprehensive.
Your mileage may vary with the surplus outlets - while the prices are usually very good, the stock range can be somewhat eclectic.Magpie - 22-4-2008 at 21:00
Quote:
I know Radio Shack is a sad shadow of its former self,
I have a theory that all businesses eventually devolve into just selling just women's clothing. pantone159 - 22-4-2008 at 23:44
As far as 'local' goes, definitely try Fry's if one is around.
I haven't messed with electronics in a long time, but my local Fry's is waaaaaaaaay better than any Radio Shack I have seen in 15-20 years. Which
isn't necessarily saying much, of course.jimwig - 23-4-2008 at 20:25
surplus and/or junk yards and/or metal recyclers
always surprised at what winds up as scrap metal
dirty metal r us
the guys who buy big lots of auction materials usually sell one or two items and stack the rest in their storage lots. some real deals there
occasionallly
places that buy the large cardboard boxes of surplus goodies from a rebuild company -- like westinghouse who does plant upgrades and yearly down time
cleanups.. they sell everything including their tools especially if the work was out of country.
most anything coming from very large companies who just want to get rid of their odds and ends.
dumpsters have been known to provide some interest and or exotaic components sometimes. i tried specializaing in targeting dumpsters of -- oh say
electronic wholesales but it wasn't any more productive than just my hit and miss routine.
of course time is a factor. and logistics etc etc.
just some methodology that has been productive for me in the past.
good hunting
jimwigssdd - 26-4-2008 at 15:19
OK so I think I may be having a dull moment here, so if this question sounds absurd it may just be...
You will see that on the diagram given it calls for just one capacitor, but on the parts list it calls for 4.
Am I missing something, or whats up here?
-ssddMagpie - 26-4-2008 at 15:51
I am sorry that I'm as puzzled about that as you are. I just had to comment that I also was going to build one of these a few years back, and I have
the circuit filed away somewhere. Then the dog stopped barking....Nicodem - 26-4-2008 at 16:35
The only places where three additional capacitors might fit in that scheme are:
1.) 0.1 uF between Q1 collector and speaker
2.) 0.1 uF between D1 output and Q1 base
3.) 100 uF at between the +/- current source as a current noise sink
But I think none of these is really necessary. The 1.) would be a good idea to run the piezzo speaker on a full wave. However, the device should work
also without them, but then again it's been more than a decade since I last played with electronics, so I might be wrong (of course, the C1 is
essential as 741 requires it).
[Edited on 27/4/2008 by Nicodem]Twospoons - 27-4-2008 at 14:39
More likely
1) 0.1uF directly from pin 7 to pin 4 on the opamp
2) 0.1uf in parallel with 100uF across the +/- supply from the battery
The above two are not exactly the same thing, though they both put caps across the supply rails.
sorry i just had to
jimwig - 28-4-2008 at 11:50
why at the cheap electrical components store , of course.
