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Old 3rd June 2015, 11:25 PM   #1
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Default Zen Mod, I built the oscillation detector, question:

Ok, how do I use this thingy?

thanks for the schematic, (Still need to add wire at bottom...

Russellc
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Old 4th June 2015, 05:08 AM   #2
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I understand it goes across the speaker terminals, but then is music played, signal input, or amp just "sits there? That doesnt seem right....

Russellc
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Old 4th June 2015, 05:41 AM   #3
Zen Mod is offline Zen Mod  Serbia
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if you take calculation :

F=1/(2 x Pi x R x C) , where R=1K and C=4n7 , you'll figure that anything is going to happen starting from 34KHz and upwards

so ,put some signal in amp, just crank it and see is it lit

though , friend with a scope is much more useful and precise
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Old 4th June 2015, 06:14 AM   #4
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Alas, no scope. Have friend with one, hes a tube guy, sure he could measure for instabiliy I suppose. I only have test tones on cd, I will string this device between speaker outputs, put some tones through it and see what happens.
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Old 4th June 2015, 07:10 AM   #5
EUVL is offline EUVL  Europe
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A couple of stupid questions :

If someone has a bad oscillation with full swing (say +/-15V), will the LEDs survive the 130mA peak current ?
If they do not, depends on whether they die with a bang or silently, no light => no oscillation, all is well ?


Patrick
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Old 4th June 2015, 07:46 AM   #6
EUVL is offline EUVL  Europe
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BTW, this (UT 61E) costs 50 USD and will measure frequency between 10Hz ~ 40MHz, amplitude 400mVrms ~ 30Vrms.
http://www.amazon.com/UNI-T-Multimet.../dp/B007THZMWI
http://uni-trend.com/manual2/UT61English.pdf

It will also measure a lot of other things useful for power amp building, like temperature, capacitance, hfe for bipolar transistors, etc.


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Old 4th June 2015, 01:19 PM   #7
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Originally Posted by EUVL View Post
A couple of stupid questions :

If someone has a bad oscillation with full swing (say +/-15V), will the LEDs survive the 130mA peak current ?
If they do not, depends on whether they die with a bang or silently, no light => no oscillation, all is well ?


Patrick
I sort of figured if they lit up, there was a problem, if not, who knows...for sure anyway. Interesting device, appears to measure temp as well. For the price, one can always use another multi-meter. Whoops, this particular model seems to NOT have temp, but that's not point of interest here anyway.

Looking at manual, set for the up to 40 kHz I presume, hook up to outputs for speakers and just measure? I suppose a signal needs injected? I think I have some old tube signal generators around here somewhere, guess its time for a good one...need seems to pop up again and again.

Russellc
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Old 4th June 2015, 01:46 PM   #8
EUVL is offline EUVL  Europe
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There are many DMMs with frequency function.
You just need to look around.

I have proper scope.
So never use this particular one before.


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Old 4th June 2015, 03:24 PM   #9
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Russel , just feed amp with music or whatever you have on test CD ;

Patrick - this circ is collected from net , as handy tool

of course that it is just a crutch , comparing to scope and some mileage of operator

so -if it is lit up , you're in trouble

if it is not lit up , and you're having problems with amp , you're in trouble

in both cases - you need help from someone who's having more mileage
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Old 4th June 2015, 05:00 PM   #10
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Quote:
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Russel , just feed amp with music or whatever you have on test CD ;

Patrick - this circ is collected from net , as handy tool

of course that it is just a crutch , comparing to scope and some mileage of operator

so -if it is lit up , you're in trouble

if it is not lit up , and you're having problems with amp , you're in trouble

in both cases - you need help from someone who's having more mileage
That's what I thought. Still, if it lights something is way wrong. That volume pot I got for BA-3 pre has a bad spot on it, sometimes just a mild pop at the same place, once in a while, volume goes up on this bad spot and some oddness as you go past this point. Hooked up to F-5 ( one with previous humm issue that tanned resistor) it "got odd" on that spot, caused resistor to tan a touch more. Hit it with IR thermometer, over 100C and it melted the plastic push button hook on things I was measuring bias with!

That channel just does not handle hum and noise well...rebuilding, have two Daniels boards with 5 watt Mills in the "tan" position and Caddocks in the more critical sound positions. New mosfets, I dont have any more IRFs left, only old Toshibas I bought a while back and some of the original Fairchild Mosfets that were originally called for. May just get set from Ha_, I like the IRFs!

I need to break down and get scope, I'll see what someone in my position needs ( not much more than job at hand, only a part time hobby Ya know) and I dont want to spend a bunch of cash, but want something up to task, assume at least 100MHZ?

Will try little device tonight.

Russellc
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Last edited by Russellc; 4th June 2015 at 05:03 PM.
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