Tubes and microphonics

[nhuwar]

I know that ceramic tubes aren't really like in audio that much and I'm not going to use them but I was wondering would they be less susceptibly to microphonics?

Just curious.

Nick

 

[SY]

After having built (conservatively) over a hundred tube amps, I have never experienced a problem with microphonics in output tubes (where you usually see ceramics). Now, I caveat this by noting that all but one of my designs used indirectly heated cathodes- filament tubes might be a different story.

 

[nhuwar]

Ok now just for my clarification microphonics sre the so to say singing of the internal structure of the tube and there in causing changes in the output of the tube's signal.

Nick

 

[SY]

Yup, that's what I'm talking about. Output tubes just don't seem to have a huge problem, much due, of course, to the larger distances and higher signal levels compared with small-signal tubes. The measures used to ruggedize power tubes also help suppress microphony.

 

[nhuwar]

I always thought it was the output tube but I never stuck my ear to the tubes on my old fender super amp but I alway's thought it was cool when I turned the volume down and here the tubes sing.

Little did I know I was only a teenager.

Thanks Nick

 

[SY]

Actually, that may have been the output transformer- I know that my old Fender amp played the Magnestriction Polka on a regular basis.

 

[nhuwar]

The output xfrm really I never would have though it but now that you said it in old high power am radio transmitter I mean old owns made by westinghouse in the 30's you could actually hear the broadcast by standing by the modulation xfmr.

Nick

 

[frank754]

I just noticed in the amp I built last month, and even in my pre-amp, when hooked up to it, if you turn the gain completely down on both, so that theoretically there should be no sound, I hear a faint tinny version of the music when I'm testing them with a transistor radio plugged into the input jack. As a matter of fact, this secondary throughput seems to be independent of the amplification, and I can hear it in the background as I turn the gain up on both, and it stays the same faint volume level.
Is this what you are talking about, and if not, what is this symptom called?

 

[Wavebourn]

I just noticed in the amp I built last month, and even in my pre-amp, when hooked up to it, if you turn the gain completely down on both, so that theoretically there should be no sound, I hear a faint tinny version of the music when I'm testing them with a transistor radio plugged into the input jack. As a matter of fact, this secondary throughput seems to be independent of the amplification, and I can hear it in the background as I turn the gain up on both, and it stays the same faint volume level.
Is this what you are talking about, and if not, what is this symptom called?

Cables?

 

[frank754]

I'm just using a hodgepodge of cheap RCA-jack-ended cables that came from earlier stereos from the 70's, not shielded, plus often cheap Radio Shack converter plugs that go from 1/4" mono to gender changers, etc. and I test this out on the living room foor on the rug, once they make it out of my workroom upstairs. Once I get my ideal rig components built they will be permanent on my stereo shelf area, and the solid state stuff will bite the dust. So you could be right, bad cabling.

 

[Wavebourn]

Some cables have piezo effect. Also, segneto-electric ceramic caps may sing.

 

[rdf]

Can't speak to ceramics but my attempts to drive a trioded EL84 with another failed due to microphonics. I believe Pete Millet ran into the same issue using EL34s as active loads in his 'Low-Mu' preamp design.

 

[Brian Beck]

If you've ever hooked a big solid-state amp up to a dummy load and played music through it, you can sometimes hear a very faint signal coming from the output transistors, especially the older ones. Probably piezoelectric forces in the silicon dice.

 

[Wavebourn]

If you've ever hooked a big solid-state amp up to a dummy load and played music through it, you can sometimes hear a very faint signal coming from the output transistors, especially the older ones. Probably piezoelectric forces in the silicon dice.

I heard that. Though 12L6 trioded driving output transistors don't sing. I like 12L6 tubes, they are as if especially designed to drive power transistors: very clean sound and no microphonics.