Piezo Electric Effect in Tektronix 5110?

[BlownUpCapacitor]

Hey y'all. I'm having some trouble with the noise my Tek 5110 produces. At certain time base sweep speeds, my 5110 will emit loud very much so audible tones. The frequency varies when I vary the sweep speed using the actual time base rotary switch and the red sweep speed variable knob of my 5B10N.

So I have concluded the tone is related to the sweep generator.

The noise, however, seems to be coming from the CRT. Or at least the actual main frame and not any of the plug-ins.

Has anyone encountered a similar problem?

[MarkT]

You have discovered magnetic deflection in CRTs - yes it will be audible sometimes as the large coils on the CRT neck are going to vibrate at the scan frequency and its harmonics and couple acoustically into the tube.

[CaptDon]

Mark T It is an oscilloscope. The 5110 is electrostatic deflection. There can be mechanical resonances in the C.R.T. excited by the sweep voltage applied to the deflection plates which cause the plates to be electrostatically attracted to or repelled from nearby elements like the G2 accelerator grid. If this is what is actually happening the effect should be reduced if you have the ability to reduce the sweep width and therefore the deflection differential voltage. You may also try to observe the effect of horizontally moving the trace with the H Position control to the extreme left or right side. Let us know what you find. Cheers.

[Alex Eisenhut]

My 547 does that at some sweep rates. Best I can figure is magnetostriction or electrostriction in some component. It's all discrete parts in there.

https://en.wikipedia.org/wiki/Magnetostriction
https://en.wikipedia.org/wiki/Electrostriction

[CaptDon]

When you look at the neck area of the C.R.T. you see those white hollow ceramic insulator sleeves on many of the leads between the grids and support structures. Those insulators move about slightly when you hold the C.R.T. in your hand and tilt it face down and face up. They make a bit of a high pitched clinking sound. Similar to the pitch heard at certain sweep rates. I always figured it was those insulators 'singing' at certain mechanical resonances excited by similar sweep frequencies or the very rapid voltage gradient during horizontal retrace. Wish we had some old guys from the Tektronix C.R.T. development lab to chime in!!! Tektronix in house built C.R.T.'s were so far ahead of their time!! I think about some of the Tek scopes from even back in the 70's where the beam could be so pin point focused and so bright it looked like a green laser beam!! 453, 454, SC502, SC504 come to mind. How about the compact 'storage' C.R.T.'s like in the SC503!! Tek really nailed it as the C.R.T. king of the hill!!!

[coppercone2]

they are the roswell aliens

[BlownUpCapacitor]

You may also try to observe the effect of horizontally moving the trace with the H Position control to the extreme left or right side. Let us know what you find.

I found that the noise decreases when the trace is horizontally shifted.

Also I managed to get rid of the noise almost completely by tightening some screws. It's still existent and still seems to be coming from the CRT. What I think was happening was the CRT was making vibrations from the deflection plates, and the vibrations transferred to metal plates that were just loose enough to vibrate a lot.

Not too sure how to describe the loose metal and vibrating part, but if you have an electric toothbrush, and lightly press it against a mirror, depending on the pressure you put, the noise will increase and decrese. Too much presure and the noise is there, but not very loud, a sweet spot of pressure, and it's very loud, not touching it at all, then yo just got your toothbrush.