matta
There is alot of talk these days about 'microphonic' tubes, though few know what to look/listen for.
It seems many of the mass made production values, in particular certain brands/types are more susceptible than others to this phenomena, but again, how to we know if a valve is microphonic in practice?
Well the good guys over at Tube Depot (www.tubedepot.com) have made this nifty little video to illustrate a "microphonic" tube.
Enjoy
Matt
Squonk
Thanks Matt for all this Amp Stuff. ?
Good stuff for clueless people like me ?
FatBoy
Thanks for that, now I know what it sounds like!
Karel-Mars
If your amp has a microphonic tube in say the input tube of the pre-amp, how does it sound? To a muso's ears it sounds like a note is added to the music. Could sound cool if you play in Sonic Youth but usually this note is out of tune with your lead solo. Sounds like you are playing wrong notes. Not cool.
The classic test is done with a wooden pencil. Remove the screen can around the pre-amp tube before you switch on the amp.
Tap the tube with the pencil (while the amp is switched on off course). If it goes "ping"
If the tube is badly microphonic, it goes "boing"
What causes microphony?
A tube is actually a lot of metal bits spot welded together separated by mica. You can see the mica biscuit inside the glass above and below the grey plates. Note all the mounting rods protrude through the mica.
But mica is brittle - when you dangle the tube next to a speaker inside a combo, the mica starts to disintegrate and the metal parts can move around. When you have strong magnetic fields in the tube (electrons flying about in fields generated by hundreds of volts) the metal bits wants to vibrate and this has an audible effect - microphonics.
Shawnvs
I like the sound of that tele.mm.
Attila
Hi Matt,
Great info to know,
Now a doff question from a newbie tube amp owner..... when your amp is power up (off standby) with or without a guit plugged in and you bump the amp head with something like your headstock (or brandy and coke ) and it makes a "micro phonic" noise like echo-ish Not like in the video
Is this the start of my woes or is this the nature of the beast - 1970 Elk Viking other than that it work very nicely
Attila
???
Gearhead
Does your amp have a reverb channel? Sounds to me like it does and if so, this sound comes from the reverb springs hitting the enclosure, each other and so forth. These springs are strung at a very low tension and supposed to only vibrate along their length. The guitar signal is fed to the one end and the signal from the other end is blended in by means of the reverb knob.
Attila
Thanks GH,
Yes it does have a reverb channel, I will have to open up and see what it is you are talking about....... A
Gearhead
There's no reason to open up your amp? It's perfectly normal for a spring reverb to induce some noises while you move the amp around, especially when it's on. Anyway, in most amps there will be a casing around the springs and this casing tends to be away from the chassis as well. If you want to know what they look like, browse the web. For instance www.cedist.com, click on 'reverb tanks'.
Sebastian
sigh... Yep my amp has started making that noise.... and funnily enough now the amp has a "useable" volume even when the two volumes (superlead channel-jumping vibe) are on zero.
