Oscilloscope output distortion pic

[deiseldave]

Hello. I just got a 465M Oscilloscope, and am trying to read up on it, and dink around a bit. The attachment is a measurement of the speaker out with my Plexi6v6 dialed a little past AC/DC type distortion. I have a 440hz mp3 wave going into the input.
Does the waveform look pretty normal to you? Or, should it be more square than saw?
The pre-distortion sine looks normal to me. But this seemed a little pointy compared to other screen shots that I've seen.
Thanks.

[VacuumVoodoo]

The slanting ceiling and floor of the waveform show that the amps bandwidth doesn't extend down to DC but has a high pass characteristic. This perfectly normal. Measure how much the ceiling drops during its half period, then google for formula how to use this to calculate -3db low end bandwidth limit.

[deiseldave]

Thanks. I think I will need to do a bit more study to know how to do this. But, thanks for pointing me in the right direction.

[LOUDthud]

Does the amp have a Master Volume that is not all the way up. I'm not seeing the power supply ripple (thickening of the top and bottom of the wave) that is indicative of power amp clipping.

Are you using an X10 probe? Do you know how to adjust the probe compensation? What does the display look like when you connect the probe to the Calibrator output on the front of the scope?

[Phil_S]

If you look on youtube, there are many instructional videos. The problem is that some are done by blowhards -- people who like to talk but don't tell you anything useful and have trouble getting to the point. Don't wait too long to move on from these. I once found one that was about 15 minutes and told me just about everything I needed to know to get started. I wish I had bookmarked that one!

Congratulations on your new (old) Tek scope. That one is a beauty. And congratulations on getting it to work!

This one is a little hokey, but I like it. No BS.
https://www.youtube.com/watch?v=zQDuZ3a6HAE

[deiseldave]

Loudthud - Yes it has a Lar-Mar PPIMV, that I thought was all the way up. I had the probe on 10X, not sure what the volt/div knob was on. I will have to learn how to calibrate the probe.
Phil_S - Thanks for the link. I was just dinking with my new toy. But, now it looks like I need to get down to some studying on it. Thanks again.

[LOUDthud]

On closer examination, I can see just a hint of ripple on the tops and bottom of waves. If the power amp is clipping, it has a high degree of filtering on the B+. A waveform like the one shown is not uncommon from a preamp into an unclipped power amp. Normally when a power amp is clipping the amplitude at the top and bottom of the wave will waver about 5% as the B+ ripples up and down.

An X10 scope probe must be adjusted to compensate for the input capacitance of the oscilloscope's input. There should be a small variable capacitor accessable near the tip of the probe or on the connector end where it plugs into the scope. The procedure is to touch the tip of the probe to the calibrator output on the front of the scope, adjust the scope sensitivity until you have a nice big signal displayed and adjust the variable cap until you have a nice square squarewave.

[sepulchre]

Nice scope. Wave looks like it sounds good to me.

[katopan]

Was this with a speaker or a resistive load connected?

Looks fairly standard for 6V6s and that type of amp.

[deiseldave]

Was this with a speaker or a resistive load connected?

Looks fairly standard for 6V6s and that type of amp.

Resistive load.

Loudthump - Thanks for the calibration tutorial. The manual is pretty in depth.