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bizzare bazaar
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Freq Band



Joined: Sep 05, 2006
Posts: 53
Location: Los Angeles

PostPosted: Sat Sep 09, 2006 6:44 am    Post subject: bizzare bazaar
Subject description: the elusive tempco....
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The local electronics surplus store.
It's a jungle of unwanted wires....the ground littered with pre-Pentium carcases faced belly up, half eaten, and dry. The smell of iron oxide, old petro-plastic, and pcb carcinogens remind's me of the Analog King who, before his passing, knew where to connect all those wires.....and why.
My weekly collecting venture began as usual.....always packing coffee, magnifying glass, and enough cigarettes to hold me up in case of rain. It never rained - but I had my smokes. And "the list". The list of things I'd heard existed, but never have witnessed in the wild.
I'd seen pictures of a Tel Labs Q81 tempco resistor, and it's image was becoming as familiar as my left foot. (my right foot looks like some old ERO mkp capacitor.)
Two years without a sighting and I was beginning to fear I would get lung cancer before I found my prize. Then today, in a flakey cardboard box high upon a shelf....there it was..... nested amongst the Mepco's, the Dale's, and the Shallco's.
Fear not to frighten it, I carried the box into a clearing amongst the 75 ohm coax trees...and with my mag-glass, found 7 more.
The store's export laws required a small fee for precision resistors - 15 cents each. I dared not reveal that these may run hundreds times more than this, and I left without affair, but with my tempcos.


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mosc
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Joined: Jan 31, 2003
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PostPosted: Sat Sep 09, 2006 10:50 am    Post subject: Reply with quote  Mark this post and the followings unread

welcome and congrats on your score.

Nice story. Be thankful you have a surplus electronics store to visit. Very Happy

Moving this over to DIY Synths forum. That's where people know about resistors and stuff like that. Very Happy

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Uncle Krunkus
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PostPosted: Sun Sep 10, 2006 3:45 am    Post subject: Reply with quote  Mark this post and the followings unread

When I lived in Sydney and was working at Jaycar in York St. There was an electronics surplus store a few doors up called David Reid. Sure we used to bag it out every now and then, saying there was more dust in the shop than components etc. but man, I miss that shop now!
There was stuff everywhere! and an unspoken understanding that interupting the guy at the desk from his programming homework to ask where something was would be met with a look of, "where am I?"
I even found styrene caps hiding in those boxes, and 120mm faders.
I can order online from heaps of places, but I won't get the chance to dig through car emissions for diamonds till I get back down to that shop.

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Freq Band



Joined: Sep 05, 2006
Posts: 53
Location: Los Angeles

PostPosted: Sun Sep 10, 2006 5:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes, I was lucky.

As you probably know already, there is the PT146 (from Precision Resistor Company).

I happened to look at the "Pacific Resistor Co" site, and saw they too can make TC wirewound resistors. So I asked them for a quote on 100 surfacemounts --- 3300ppm, 1k, 1%, 1/2 watt.
I'm awaiting their reply.
http://www.pacificresistor.com/

I wonder if surfacemount's will work? One problem might be placing it on the correct part of the IC.
....or what if you mounted 2 or more resistors per chip, in series, that add up to your resistance needs? (e.g. 2@ 500ohm for 1k ohm, and 4@ 500ohm for a 2k ?) That would span more area across the chip.

I just came across some unknown scrap military circuit boards that have an RCA CAxx chip. Mounted on that chip are 4 or 5 sensors (thermistors? or tempcos?)....no markings, they are wired to the board and bent over and glued to the chip. They look like round BB's with wires, and the circuit board says R-5k (I assume 5000 ohm).

How does one test for a thermistor?
" " " " a tempco?


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toppobrillo



Joined: Dec 10, 2005
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PostPosted: Sun Sep 10, 2006 5:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
How does one test for a thermistor?
" " " " a tempco?


well, you measure the resistance with an ohmmeter, then vary the temperature around it and see.. you can even use your fingers or breath to do it.. or a hair dryer or the freezer!

as the temperature chsnges, the resistance will too. up temp, down res. for an NTC kind, up temp up res for a PTC. i have a couple NTC thermistors myself. have a look at
Rene Schmitz site if you haven't, there is good application there for your cheap thermistors. also, Takeda Motohiko has followed suit and there are some experiments there.
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