uA726 replacement

[harry bissell]

The 3046 problem is that pin 13 (substrate) must be at the most negative
potential... The expo pair usually needs to run at least one diode drop below
ground (in most schemes I've seen). This needs at least a slight negative
supply (a volt or so).

Here's a schematic (posted before) of a 3046. The differential pair is the one
I've left because I guessed that would be the most useful. Tom G. has a scheme
that uses one fewer internal transistor... this is possible here too.

JH (i think) pointed out that the 3046 has limited voltage capability so my
design is "pushing it" with the negative 6.9 volts. Worst case Vceo is only 15
volts, Vcbo is 20V... Typical is 24V and 60V so most parts should work.

I have a crude graph of the thermal performance both compensated and
uncompensated. The test conditions were heat unit in cardboard box... and
measure during decat to room temperature.

I think a surface mount 3046 could be used as a "module" and then dipped in
vinyl or something to protect it from air drafts (a killer).

I'm planning a test of a MAT01 (TO-5) heated externally with the heater chip of
an LM399 temp stabilized zener (don't use the zener). This is a $4 chip, plus
the cost of the MAT01 (or 02). If It works I'll post it here. :^) Harry

Grant Richter wrote:

> I would like to thank jbv for even trying to get a
> group buy together. It's a shame it didn't work out
> but the work he put into it is certainly appreciated.
>
> The uA726 is a thermostated NPN matched pair in
> a top hat can. A reasonable substitute would be a
> thermostated LM3046 or MAT02 transistor array with the
> pins brought out to the appropriate copper pattern.
>
> The problem is the uA726 did not require -15 volt
> for thermostating. The heater operated between
> +15 and ground.
>
> The question is: Is there a LM3046/MAT-02 thermostating
> scheme "blessed" by this group, and can you get it
> to run using a single supply op-amp?
>
> ----------
> > From: Andrew Schrock <aschrock at cs.brandeis.edu>
> > To: Mike Granger <mgranger at greenville.infi.net>
> > Cc: jbv <jbv.silences at wanadoo.fr>; Quinton Fulsom <qfulsom at usa.net>;
> synthDiylist <synth-diy at mailhost.bpa.nl>
> > Subject: Re: Bad news : Ua726 depleted
> > Date: Thursday, August 12, 1999 3:59 PM
> >
> > If you're going to go this route, isn't there a small-PCB replacement
> > version of the uA726 manufactured? I seem to remember it was produced,
> but
> > not cheaply, by some UK synth company. Analog solutions perhaps? I forget
> > the name, but I seem to remember the price being around $90. Maybe
> > somebody should think about a DIY version?
> >
> > Andrew
> >
> > -| Andrew Schrock | aschrock at cs.brandeis.edu |-
> >
> > On Thu, 12 Aug 1999, Mike Granger wrote:
> >
> > > I know this is a long shot, but there was a part manufactured by
> National
> > > Semiconductor with a part number : LM726; ( I think) and it was
> supposedly the
> > > equivalent to the uA726. This part was not manufactured for a long
> time, but
> > > stock of it might exist somewhere. Just a thought.
> > >
> > > Mike Granger
> > > Greenville SC
> > >
> > > jbv wrote:
> > >
> > > > Quinton Fulsom :
> > > >
> > > > > So before we start going off here please verify and post your
> "sources" in
> > > > > which your deriving comments and defining what I've said.
> > > > > Quint
> > > > >
> > > >
> > > > Actually, Quint is right : I just checked my source and the stock
> > > > is NOT AVAILABLE ANYMORE (although it was still available
> > > > last week when I forward my original offer to AH).
> > > > Anyway, if it's true, it really pisses me off to learn that someone
> > > > bought the stock the day after my original posting...
> > > >
> > > > There are other stocks available, but the quote is so high (more
> > > > than 10 times the price I announced in my offer !) that it
> > > > becomes ridiculous...
> > > >
> > > > So what's the conclusion to this thing ? I'm not sure...
> > > > Actually, I came across that quote for uA726 as I was
> > > > looking for other parts, and I thought it could be
> > > > interesting to run a group order through the lists...
> > > >
> > > > It is clear that we've been acting as real newbies,
> > > > but was there any other way to run a group order ?
> > > > As a humble hobbyist, I wasn't going to invest $3000
> > > > before knowing exactly how many ppl would be interested,
> > > > and get stuck with 50 or more unsold chips...
> > > >
> > > > Sorry for disapointing you folks... I'm sure these chips
> > > > will reappear on the market sooner or later, but the price
> > > > won't be the same...
> > > >
> > > > jbv
> > >
> >
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