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Testing Recievers with Oscope

pjf610

pjf610

Active Member
I am a newbie and want to check the outputs using an Oscope, I have a tecktronics 2232 OS, a Fluke 6070A signal generator, and a HP 8116 function generator, these units was handed down to me from my uncle. My question is what type of connector do i use? I have a bnc to rca but it is not split only 1 rca at the end, so my question is when i plug the bnc into the signal gen. i plug the rca into the aux.how do i read 2 channels or do i have to switch the rca to each right and left every time i what to see each channel. I watch the videos on YT and they can switch from left to right on the OS do they use a bnc cable with 2 rca plugs on the end???
 
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Hi , I do this a lot and have two answers/approaches for you. 1. You can split the input to two outputs with a bnc splitter and then put an rca on each end of a cable to each channel input , I usually use Aux. or 2. you can use a two channel function generator as I do which has a lot of advantages. I use a HP 3300a that I recapped and only spent about $80 total. I did not read up on the 8116 but I will look to see if it has two channels. The third possibility would be as you say switch each channel. I am sure you know but its worth mentioning you would want to do this testing into a dummy load. If you would like more specifics let me know and I can outline the procedure.
 
WOW thanks a lot i really appreciate this, any learning experience i can get would be great, I have bnc splitters so that answers that question you say do testing on dummy load what is meant by that??? Can you see if what i am doing is correct,
1st connect the SG to aux on receiver
2nd connect both channels on the OS to the speaker left right
3rd feed a 1K signal to the receiver
4th see results on OS
does this seem right to you???

Thanks Pat
 
A dummy load is a large resistor of 4ohms or 8 ohms (depending on what speakers you want to emulate) that you hook into the speaker terminals in place of speakers when testing an amp. The amp needs a load to test it, and these lend a constant load as well as preventing damage to speakers. These get hot quickly with large amps. You should have one for each channel. They come rated in Watts, and you want considerably more than you plan to test so they don’t get too hot. I use 200 watt 8 ohm dummy loads like the one in this link. You could get 100 watt for about half the price if you are working on lower power receivers.
Steve

https://www.parts-express.com/8-ohm-200w-non-inductive-dummy-load-resistor--019-030
 
OK I see what you are saying, so do i hook up the scope to the ends of the dummy load??? Do i need to purchase 2 of them???
 
Yes and yes, but you need to be careful when connecting an oscilloscope to the output of a receiver/amplifier as not all have the so called ground connection for the speaker at ground.

This has been posted before, but it is good information for someone just starting out with an oscilloscope.

 
Let me ask you this i watched the you tube videos from blueglow and Brad Freeman ( working on a 2250B) they show that they hooked up there SG to the aux inputs on the unit and show the Oscope with the sign wave on it, are they using a dummy load unit with it?? they do not say they are or are not, so i am a bit confused
 
I am a noob to the oscope world also, so I don’t always know the theory behind what I am doing (trying to learn). I don’t know if there are tests you could run without a dummy load, but if you want to know what your amp is doing with a signal at various power (volume) levels (clipping, etc.), you need to be able to make the amp work under stress (load). Otherwise, when turning up the volume, you aren’t loading the amp and getting a true picture of what it is putting out in actual use. So, if you are testing the unit without speakers, I would guess you normally need dummy loads. If you just want to see your input signal and outup signal at the same time on a single channel - at lower listening levels - you can do that with speakers attached and Oscope across the speaker terminals. For power tests, etc, you would damage your speakers turning the volume up to clipping, so dummy loads required. I hope I have all of that right.
 
I have been using oscopes so for 40 years....

My best advice for a beginner.... Get a hand held battery powered unit.....

I own 4 scopes... A Tek , a pc based, a heath kit and the hand held....


Which one is used by far the most?

By far .... The hand held..... And you don't have to worry about grounding issues.....at all....

But they each have limitations.

Johnk
 
For audio? Just fine for me.

Not for high speed stuff....

Some of the newer ones are actually pretty good...
 
So yes lots of good advice here ! I have a tektronix 2245 I like a lot and my setup is to send a 1000 hz signal out of the signal generator and in your case then split it with the BNC splitter then two BNC cables to RCA adapters to AUX in on the amp. I have the speaker terminals hooked up positive and negative to a 200 watt 8 ohm resistor on each channel and I set the oscilloscope for 50v. I take the grounding clips on the probes to the chassis ground on the receiver via a wire and hook my probes set on 10x to each positive speaker terminal of the front speaker set. I then hook a voltmeter up on one channel and set it to AC voltage. So once its hooked up as above I turn the volume up and monitor the oscilloscope to see when it first clips. The voltage should be around 24VAC for a 2270 at this point. The math is: take the voltage, square it and divide by the resistance to equal watts. So in this case 24 squared is 576 and divided by the 8 ohm dummy loads is 72 watts.
 
Thanks a million for all your help, once i do it it will be one thing less i have to ask about
 
No problem, its how we all learn this stuff unless we are EE's which I am not but would like to have been along the way. I am happy to answer any further questions you may have either here or in a PM. I have restored about 200 items and only really began fully testing them about halfway through after learning how to chase the signal through the circuit. Its FUN !!!
 
Your scope is a 2 channel scope and can measure and display both channels at the same time.
 
Organic chemist here, been building kits and goofing around since my youth before Radio Electronics magazine and heath kits went away. Picked this back up about 5 years ago in between jobs and closed an estate of unbelievable magnitude. The guy collected his whole life and filled his house and two double garages floor to ceiling with audio gear. I fixed everything from tube gear fishers to solid state sansui stuff ! I finally got the bug to get a scope to troubleshoot more effectively. I am now insane enough I plan to learn how to do FM alignment although cheating a bit by using sound technology gear to make it easy. Never used a handheld scope but sounds quite interesting !
 
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