[time-nuts] Totally unrelated, but..

Bob Camp kb8tq at n1k.org
Wed Dec 7 16:11:53 EST 2016


Hi

There are a *bunch* of people making stuff like 78xx regulators. Even 
20 years ago, there was a lot of difference between brand M, brand T, 
and brand F on these devices. Today the spread is even larger. Toss in 
outfits that sub contract the work to who knows where this week ….
What you get today may not be what you got yesterday or what you 
get tomorrow.  At least 20 years ago you got the same thing when you
re-ordered. 

Crazy stuff 

Bob


> On Dec 7, 2016, at 3:16 PM, Clint Jay <cjaysharp at gmail.com> wrote:
> 
> I was looking for a low noise regulator to power a log amp/detector earlier
> this year and was rather surprised to find the 78xx regulators were
> considerably better than many of the "low noise" devices.
> 
> But!!
> 
> I've also had odd experiences with some brands of 78xx devices (and way
> before the 'net was anything more than SLIP dial up to a shell so I doubt
> they were Chinese fakes) ,  one was bad enough that it gave some very
> random voltage measurements on a digital meter,  turned out of the was
> creating all sorts of RF hash in the low VHF range up to and possible
> beyond the FM broadcast band.
> 
> On 7 Dec 2016 20:10, "Joe Leikhim" <jleikhim at leikhim.com> wrote:
> 
>> Could the low noise parts actually be counterfeit, relabeled as such?
>> 
>> Is the circuit the regulator feeds sensitive to a narrow band of voltage
>> that the "good regulator" is outside of?
>> 
>> Try replacing the regulator with a battery supply and resistor divider to
>> attain the working voltage. Move the voltage around. A good potentiometer
>> and stiff filter capacitors are recommended so as not to introduce "pot
>> noise".
>> 
>> Is something corrupting your test procedure?  I had a circuit that
>> misbehaved due to floating logic pins reacting to static electricity on the
>> work bench. Another time a diode was photosensitive.
>> 
>> 
>> 
>> --
>> Joe Leikhim
>> 
>> 
>> Leikhim and Associates
>> 
>> Communications Consultants
>> 
>> Oviedo, Florida
>> 
>> JLeikhim at Leikhim.com
>> 
>> 407-982-0446
>> 
>> WWW.LEIKHIM.COM
>> 
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