16 Nov
2012
16 Nov
'12
3:59 p.m.
On 11/16/2012 4:14 PM, allison wrote:
I use 2N3904s a lot for switching and RF applications
and it's a good
all round device.
Typically when I buy them I get 100 at a time as I use them for Zeners
(base-emitter
reversed is about 7V), Varicaps (base-collector reverse biased), High
conductance diode
(base shorted to collector) and of course as a transistor. Generally I
pay about 3-4 cents
(US) for known vendor parts.
What I was wondering was how much it would cost today ( single sided pcb )
and modern parts, compared with the original product. I wonder what
speed leds
work at, and use them for switching diodes. The advantage is a nice visible
logic gate. Hmm, A blue transistor when on would be nice too!
Another device that is newer than the old bipolar
transistor days are
the MOSFETs
specifically those in the 2N7000 and similar class as switches. They
offer very low
on resistance and high noise margin with the gate turn on voltage in the
3-8 Volt range.
Any one using them in quantity would do well to create a go/no-go tester
for leakage
and gain as a project like that will consume a lot of transistors and
marginal ones are
a big nuisance.
For diode the 1n914 and the 1n4148 are good choices for DRTL style logic.
I am planning at the momement using 2901's, a nice 10/20 bit computer.
20 address bits, 4.77 mhz clock , byte access bus, and front panel - The
PC* killer . :)
1976 ish era mini-computer, rather than micro-computer with a micro-chip.
(Of course if any wants to put this design in silcon, feel free to do so) :)
Allison
Ben.
* At the moment a design with static memory, now for dynamic memory
refresh cycle
I would have to check if it will fit in the micro-code rom.