Mistakes

A "read the manual" recent blog post:

https://wb9kzy.blogspot.com/2025/06/read-manual.html 
 

I got an email from a customer with a kit problem at almost the same time as I was having trouble with something on the bench.  The customer had installed all the components on the circuit board but I suspect he never looked at the web page or any of the three pieces of documentation.  If he had checked the docs first, the diodes which burnt out (and burnt out a 2nd set as well) would NOT have been installed in the first place:

I thought that the red made things clear, maybe not ?

Simultaneously I was working on a Wien Bridge audio oscillator using the LM386.  I was having lots of trouble with the circuit oscillating at RF which looks like fuzz on the waveform:

the lower part of the wave looks like it grew a beard of oscillation ?

Finally I watched the start of a Youtube video on this circuit:

.

source: https://www.youtube.com/watch?v=WAIKevh38gU

where he mentions the somewhat unusual circuit which has two resistors for determing frequency which are 4.7k ohms and 47k ohms - usually these would both be the same in a normal opamp Wien bridge audio oscillator circuit.  As soon as I saw that I stopped the video and made the change and the circuit started to work:

this looks much better !

Moral for today: read the manual, Read The Manual, READ THE MANUAL !   :)

Update: incidentally there is a mistake in the frequency formula on that slide above, it should be:

 

frequency = 1 / (2 * Pi * SQRT(R1*R2*C1*C2))

 

 I tried plugging that formula from the slide above into a spreadsheet and it didn't work until I pulled the 2 times Pi out of the square root  :)

So "read but verify" is the 2nd moral for today ? 

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm