|Testing LM308N National Semiconductor
older (New Old Stock) ICs.
Testing them to make sure they are good
parts -- and..I will be experimenting a bit
with this circuit over the next little while. I
do own an electric guitar..and (who
knows!) ..the next Eric Clapton?????
|Someone who is a guitar enthusiast has shown interest in the LM308N (1984) vintage ICs that I have in my
collection. I have about 35 or so that I got given to me by several older ham radio guys who were downsizing
their parts collections. -- Alot of the stuff I get..seems to be of little interest BUT.. there are certain parts that
the audio gurus really like to use. They tend to like the older original parts and not the cheap knockoffs from
China. -- I have bought some good parts from China. They worked when I plugged them in to the circuit.. but I
have also bought some real junk. Any parts I buy from Asia..I test them before I sell them and send them out to
people. FOR THOSE INTERESTED IN MY PARTS THAT I SELL..HERE IS A LINK TO MY BIG SUPERLIST OF PARTS.
www.earlandrews.com (mirror sites- same content)
established in 2005 - Free ON LINE HAM MAGAZINE
and also I sell parts and do the odd repair.
In this article: (Aug 29th 2014) - I stray into Audio
circuitry work, prototype, expermentation and testing of
Audio components. (LM308N)
|Here is one of the circuit diagrams for this "RAT"distortion guitar fuzz machine! -- I know little to nothing about the
fuzz boxes but since 2005..I have had a fair number of audio people write me about Germanium Transistors (I do
sell some) and certain other parts associated with this equipment. So..today..I finished building the above circuit.
For my initial testing.. I left out the CLIPPING STAGE AND THE DIODES D1 AND D2 AND THE TONE CONTROL. All I
wanted to do today is plug some of the LM308N 8 pin ICs into the socket in my prototype circuit (breadboard) and
make sure THAT THEY WORK! -- Ive got the circuit working now and the first LM308N I plugged in works fine..see
the output amplified (and somewhat clipped) wave form. -- I used a Function Generator in my lab to generate the
input wave. Output was measured with an Oscilloscope at C7. I terminated R6 to ground for this initial testing.
|This old Heathkit Logic prototyping test facility gave me the necessary DC
voltages. For the +4.5 volts going to pin 3 of the IC..I used the +5volt and for
the +9 volt.. I used the +12volt DC voltage and dropped it to about +10volts or
so by using 3 series rectifier diodes.
ITs a bit of a lashup ...but it works. I am going to build a better more permanent
circuit in the near future on a proper electronic proto board and solder the
leads and make it much neater. I will be trying it with my electric guitar as well.
|I used this function generator set to around 2 khz and
the amplitude was very low to go to the input of this
distortion amplifier circuit.
|INPUT from the Function Generator
|OUTPUT from the circuit. - below
shown on the scope. Amplitude is
rounghly 7 times higher than the
Amplitude of the input.
Plenty of amplification and there is
distortion (which is what is desired
in the case of fuzz boxes).
|August 29th 2014... MUCH MORE TO COME. I plan to test all the LM308Ns (National Semiconductor ICs) (8 pin op amps) in my collection of parts.
I have about 35 or so and I will search for more. These are particularly interesting parts for use in these Distortion FUZZ boxes..which I know
very little about really.
I have been working with ham radio parts and radios..BUT..it never hurts to diversify and I could use a few extra dollars every now and then.
The Audio people have contacted me from time to time searching for old Germanium Transistors such as OC44s. They want certain ranges of
HFE and low leakage. -- I will be (this winter)..building a leakage tester for Germanium Transistors. There are plans on YOU TUBE and videos
about this sort of thing. --->>
This is the sort of work I do in my early retirement days. I am 61 and took an early retirement from a job in the Federal Government in 2005. I
have been collecting parts (mostly old ham radio parts) and have been working at fixing older solid state radios and I take the odd job (by mail
order) for my very modest $10 per hour shop rate! -- KEEPS me busy and I really enjoy working on stuff and talking with people and opening up
the boxes of goodies they send me (sometimes only for the cost of postage!). -- I DO TAKE DONATIONS OF OLD SOLID STATE PARTS AND
BROKEN HAM RADIOS AND STUFF LIKE THAT. I test the parts and keep some for myself and sell some here and there.
NOW.. I'm starting to work on these Guitar Fuzz boxes and learning about them. I do have a guitar. A cheap Electronic Guitar which I pick up
only occasionally and maim the thing! Im a very poor player and in fact..Id say..I cant play! -- NO matter.. I will start working on this RAT Fuzz
I plan to build the circuit (PROPERLY) into a little metal case with the pots and labels and make it a nice looking and hopefully very functional
|I TEST ALL MY PARTS.. AS
MUCH AS POSSIBLE.
I do have an IC tester that I
bought from EBay for around
$40. It tests quite a few OP AMP
types like 741 and 324s but not
the LM308. So..what I did is I
built the actual circuit to test the
35 parts I have.
I try and do this as often as
practical.. THAT IS.. TEST THE
PARTS BEFORE I SELL THEM..
Particularly in the case of NEW
OLD STOCK. NOS.
Sure ..they look new..but who
knows how long they have been
in storage or if they even work.
THATS WHY I TEST MY PARTS.
FOR VERY COMPLEX PARTS
SUCH AS 40 PIN
MICROPROCESSORS or certain
other complex linear ICs..I will
sell with a
Gentlemans Agreement. Try
the part in your circuit.
IF IT DOESNT work.. I will give
you a full refund.
Since 2005 I have only had to
issue 2 refunds. I have done
hundreds of small orders since
Its on the scale of a hobby at
this point. My expenses still
out-weigh my income. Thats a
hobby in my books. -- I only work
at this stuff in my spare time.
|end for today.. this page is going to be added to
very soon. Watch for more projects along these
lines this winter comming. Cheers...Earl