My SVT is making a bit of a ringing noise, oddly it seems to be something amplified. Without the amp plugged in, I think I know what is going on, but don’t have a clue why, or what part is causing. The video tells the story much better than I can.
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Odd microphonic noise in my SVT.
- Thread starter Bulltrout
- Start date
Yes. Turn your amp on, volume up, guitar volume down. Tap each tube lightly with a pencil or chopstick. You’ll find the “ringers”, the microphonic tube(s).
Usually on a vintage SVT it’s the 6C4. I’d start there if you’re going to be chopstick testing.
They’re cheap enough, I’d buy a couple a see which one is quietest. I have a handful in my tube drawer for this exact reason.
www.amplifiedparts.com
They’re cheap enough, I’d buy a couple a see which one is quietest. I have a handful in my tube drawer for this exact reason.
6100 / 6C4WA, Triode, Medium-MU Vacuum Tube | Amplified Parts
The 6100 / 6C4WA is a heater-cathode type medium-mu triode of miniature construction, suitable for use as a class C amplifier and oscillator. This type is characterized by long life and stable performance.
www.amplifiedparts.com
Thanks everyone. I’ve had microphonic tubes before, but never like this; you learn something every day. Changing a tube is easy enough, but making sure it matches the set and biases properly is something else. Off for a quick trip to my tech.
Preamp tubes are biased by the fixed resistors in circuit. No biasing needed. On the odd chance it isn't a tube, some caps, usually ceramic, have been known to become microphonic.
True, my mind immediately went to the power tubes, when you guys are mostly talking about the preamp tubes. I should learn to listen better…my wife might be on to something.
I think the pitch of that is more likely to indicate a power tube, it might be too low to be a preamp tube. I'd expect a preamp tube to have a higher pitch than that and probably not as loud. Could be wrong though. And yes, the 6C4 is famous for being microphonic. If it turns out to be that one, better buy a bunch and hope there's one or 2 of them that isn't microphonic.
If you want to rule out the preamp pull the 6C4 and try slapping the amp again like in your first video. The 6C4 sums the two preamp channels together. If that tube is out and the percussive maintenance still gives you the ringing then definitely somewhere in the PI, driver, and power tubes. The ringing like that when subjected to vibration/mechanical impact does sound like a microphonic tube to me.
Given the noisy nature of 6C4 in general a rough smack with the chopstick like in your second video might just be accentuating noise in an inherently noisy tube. I only listened once and mostly heard the crackling and thump of the impact, but does it produce the same ringing noise when tapping the 6C4?
Given the noisy nature of 6C4 in general a rough smack with the chopstick like in your second video might just be accentuating noise in an inherently noisy tube. I only listened once and mostly heard the crackling and thump of the impact, but does it produce the same ringing noise when tapping the 6C4?
IMHO based on the video, it does not appear the 6C4 is the source of your problem. Otherwise, you should get the exact same ringing sound when you tap 6C4.
The 6C4 in my skunk rattles if I place the amp on some of my cabs. . I researched to learn which 6C4 variants are the best bet. Bought several and none of them are great. All of them are microphonic to some degree and all of them inject a tink sound if I do the chop stick test. Based on what I have read, this is normal for a 6C4. I definitely have a better option than the tube in the amp, but none are great. My solution was to put the amp on a different set of cabs that does not cause the tube to rattle.
How did you make out after? More importantly, is it spring in Edmonton yet? Because we still have snow on the ground in St. John's.
