[volt-nuts] Making a Reference IC

Dave M dgminala at mediacombb.net
Mon Sep 14 18:45:22 EDT 2015

After making a mess in my garage while searching for it, it turns out that 
that my Fluke is a 731B.  It appears to use the same Voltage Reference IC as 
the 731A, so no big deal there.
I found a previous discussion about the 731/732 reference ICs.  Seems that 
the ICs are either from Motorola  (MCA1914/MCA1924/MCA1934) or GE (RA3). 
Doubtful that GE continued production of that IC very long, so my guess is 
that these are Motorola parts.  It's all moot, since none of the parts are 
still in production.  I'm afraid to contact Fluke for a quote on the 
IC/Resistor set.  Don't think my heart could stand the shock.

I'd really like to get this unit back in operation, but I don't want to 
break my bank account to do it.  I have a few LM399s on the shelf, so I 
guess that will be my best approach to a repair.

Thanks for the discussion,
Dave M

M K wrote:
> On 12/09/2015 23:12, Dave M wrote:
>> I realize that better references are available.
>> I was thinking of resurrecting a long-defunct Fluke 731 that I have
>> in the garage.  The reference IC is bad in it, and (1) I don't want
>> to throw it away without a meager attempt at repair, and (2) I don't
>> want to spend a lot of money on it because it's in pretty bad
>> physical condition.
>> I was hoping that someone could lend a touch of advice on those old
>> references.  I have a few 1N827A reference zeners, and a washtubful
>> of transistors.  Maybe something could be cobbled together that
>> would get the 731 back in operation.  Maybe not to original specs,
>> but close, which is better than nothing.
>> Thanks for your reply,
>> Dave M
>> Jack Mcmullen via volt-nuts wrote:
>>> Just thinking why would you reinvent a transistor/zener reference
>>> when the industry's voltage reference chips are in the $2.00 or less
>>> single quanities with performance far exceeding anything previously
>>> available in discrete components??
>>> -----Original Message-----
>>> From: Dave M <dgminala at mediacombb.net>
>>> To: FEBO Volt-Nuts <volt-nuts at febo.com>
>>> Sent: Sat, Sep 12, 2015 1:58 pm
>>> Subject: [volt-nuts] Making a Reference IC
>>> I was looking at the schematics for the Fluke 731 and 732 voltage
>>> references.  these, and several other brands and models of voltage
>>> references, use the same or similar reference ICs as their basis. The 
>>> reference ICs are a Zener/NPN transistor pair on a single
>>> substrate. Please view in a fixed-width font such
>>> as Courier.
>>>        |
>>>        |
>>>      C |
>>>        |
>>>          |
>>>          |
>>>           |----
>>>           |  B
>>>          /|
>>>         / |
>>>      E |
>>>        |
>>>        +---------------
>>>        |
>>>     /------/
>>>       /
>>>      ------
>>>        |
>>>        |
>>> Just thinking... would it be possible to make a reference with
>>> similar characteristics with discrete components (a low tempco
>>> Zener and a transistor)?  They would likely have to be closely
>>> coupled thermally and
>>> maintained at a constant temperature within an oven or by a peltier
>>> device.
>>> What criteria would apply to the selection of the parts?
>>> Dave M
> There has been some of those references available second hand from
> ebay, mostly pulled, but some may be counterfeit, so look for sellers
> with pictures showing it as old.

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