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Author Topic: Essential Components  (Read 28950 times)

Posts: 14498

« Reply #30 on: October 05, 2012, 06:04:57 AM »

What, in your estimation, are the essential components for a home brew electronics component toolbox? I'm talking transistors, diodes, ICs, and other assorted items. Standard value resistors and capacitors are assumed.

Mouser or Digikey. Parts are only 4 days away and you don't have to keep your own inventory.

Bob  AA4PB
Garrisonville, VA

Posts: 167

« Reply #31 on: October 05, 2012, 09:30:28 AM »

If you have some equipment that you figure on keeping, check the ICs: it is by no means unknown for some of them to become 'unobtainium'.

Posts: 2409

« Reply #32 on: October 06, 2012, 09:54:33 PM »

If anyone answering here sent you a piece, you might get your supply for free  Grin

Posts: 2088

« Reply #33 on: October 08, 2012, 11:27:00 AM »

adding to G3RZP's advice... older equipment using EPROMs are likely to start going bonkers, early generations of EPROMs and flash have greater instability over time than the new stuff.  worth using somebody's PROM burner to make a safety copy of the contents on several media, and/or copy the programming to a new part.

this doesn't work as well with a lot of CPU/MEM/ROM combo chips, alas.  if you look enough, you can find a raw chip.  but if you check the data sheet before you buy, you may well find they are NOT readable once burned... either because of a fuse-wire blow the programmer performed to keep you from looking, or because they are externally write-once, read-none.

yet another reason you probably won't see any of today's rigs on the show-and-tell shelves ready to plug in and work in 30 years.  between unobtainium and unreproducium, we're not making any more lifetime-plus electronics.

Posts: 13

« Reply #34 on: October 20, 2012, 04:10:31 AM »

hoarding Silver Mica Caps these days Smiley
And anytime we mod/change parts on pcbs at work, I keep the old parts.

Posts: 325

« Reply #35 on: October 20, 2012, 05:41:15 AM »

As mentioned previously the venerable 2N5179 is a good choice.
However you may find leaded case devices are not available. To
solve this dilemma you can either make or build PCB Adaptor boards
which will accept the SMT variant of the 2N5179 (MMBR or MMBT 5179)
and allow soldering leads to the PCB.

Consider also that a 2N5179 made by Motorola, Fairchild, National and
other vendors will often exhibit different Beta among the differing
vendors. So if possible buy yourself a batch of the individual devices
so you can avoid some of the aggravation of dealing with subtle
differences between differing vendors.

Surface mount cap and resistor kits are available from vendors out
there such as Mouser and Digikey. I tend to build my own kits as it
eliminates the odd caps which will likely never be used in my designs.
I have had good luck buying interlocking bins on e-bay with snap
cover lids to assemble customs kits were the stepped values of
caps and resistors can be arranged within the range of magnitude
and ordered to easily locate.

Solid state components are a little more painful. Simple function
silicon for rf amplification is pretty straight forward. Integrated
circuit silicon is a little more hairy as many ic's are optimized
for discrete frequency bands. Vendors aggressively redesign
their product line up to address shortfalls in the product design
and to add features which make the product line more marketable.
One thing you will discover if not already obvious is that a vendor
will often release a new IC which will be sold to replace the older
product feature wise and incorporate new capabilities but use
dramatically differing pin outs.

I select my active devices for frequency range, noise performance,
dynamic range, and availability. If it is currently in production that
is a good omen, if it does not have a notice out from vendors of
"DO NOT USE FOR NEW DESIGNS" that is even better. While I do
pay attention to power consumption my component selections are
not driven by ultra low power performance. Good 3rd Order performance
normally implies the need for current far beyond sub mA component
operation so parts speced for uA service are not abundant in my inventory.

Capacitor selection is a little more dicey. I try to select caps with NPO
specs and from known quality sources. In particular I am wary of surface
mount caps especially multilayer chip capacitors. I am partial to ATC
and Johanson NPO values for use in filters and tuned circuits. While
many seem to function well at 1 to 2 MHz I discovered the hard way
that many have losses at 100 MHz which impact the circuit performance
more than the inductors with measured Q of 100.0

The same care should be exercised in selecting surface mount resistors.
Pay close attention to the resistance change as a function of temperature.
Also see what their breakdown voltage spec is.

While many say you do not need to use special solder I strongly recommend
using 62% tin, 36% lead and 2% silver. Surface mount terminations
have improved greatly but unless you know for a fact what the surface mount
device termination is made of use the silver bearing solder. Many still exist
which will suffer leeching problems if using non-silver bearing solder often
causing the termination to delaminate from the component.

Keep in mind that surface mount components were designed for temperature
controlled attachment methods where the temperature is raised and lowered
in an oven to match a profile speced by the part manufacturer. A good assembler
can attach parts with an appropriate iron, solder and tools and obtain good
results but the fact remains that many parts are not intended by the manufacturer
to be attached by hand.

Surface mount parts allow the realization physically small
circuit designs but one must pay close attention to component selection
when using inductors in tuned circuits. Small and high Q typically are
mutually exclusive so even though you can save pcb real estate with the
small parts you may find your inductor requirements will consume the space
you saved.

Hope this helps.

Chuck WD4HXG

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