[sdiy] Tempco, was Transistor help

[James Patchell]

http://www.oldcrows.net/%7Epatchell/matcher/matcher.html

At 04:30 PM 4/26/2005 -0700, Harry Bissell Jr wrote:
>Really, what you want to do is match for the same
>base-emitter voltage drop at some particular test
>current that is in the range you will use. Usually
>100uA is a good place to start.
>
>Pass 100uA through the base-emitter junction and
>measure the voltage. Pair those that are within
>1mV or so.
>
>There are schematics online for the test jigs that
>Bob Moog etc used to do this. Fess' up if you've
>got them on your site.
>
>Higher beta is better for other reasons, but usually
>no for matching.
>
>DO NOT touch the transistors you will test, the warmth
>of you hands will change the reading VERY much. Use
>tweezers or something like that.  I have used the
>Pomona "mini hooks" to pick up the part by its leads,
>Don't test in sunlight, or drafty place, or near heat
>vent.
>
>Once you match transistors, use them in pairs and its
>best to tie them together with epoxy, or a copper clip
>(hard to find these days) or thermal compound between
>them... or I sometimes use thermal compound and a
>little piece of heat shrink tubing over them.
>
>If it is for an expo converter, the tempco should be
>thermally coupled as well.
>
>I use the 2SC1583 (NPN pair) and 2SA798 (PNP pair) as
>alternatives to matching (they ARE matched) but have
>the emitters tied to one pin (good for expos, bad for
>Moog ladder...)  The 2SC3381 and 2SA1349 are good
>pairs that are separatr.  The CA3046 is a five
>transistor package in a 14 pin dip, matching and
>thermal coupling are quite good.  Cost of the 3046 can
>be as low as $.25 in 100pcs. lots  (cheap  !)
>
>Good luck
>
>H^) harry
>
>
>--- Fiercefish <fiercefish at btinternet.com> wrote:
> > Thanks to all who replied, I have tested a bunch of
> > the transistors and the hFE varied from about 130 to
> > 200, I found about 8 that matched at 166, do you
> > reckon this would be ok to use in the soundlab
> > VCO's? From what I can gather a matching hFE is
> > better than just randomly sticking any pair in but
> > not as precise as the traditional method, no?
> >
> > Also re the tempco's would these be suitable?
> >
> >
>http://www.maplin.co.uk/Module.aspx?ModuleNo=2218&TabID=1&source=15&WorldID=&doy=26m4&Cache=#CacheID
> >
> > The design calls for 2k PTC but would I be able to
> > use the 4.7k above if I changed the circuit a bit?
> > Any thoughts welcome!
> >
> > BTW I promise to post some pics up when I finally
> > finish the Soundlab, it will look pretty cool in a
> > nice old hardwood cigar box with an aluminium panel
> > and cool wide skirt numbered knobs.
> >
> > FF> No virus found in this outgoing message.
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> >

         -Jim
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