Wednesday, May 21, 2008

Don’t Let Tube Rattle Rob Your Tube Amp Tone

Tube amp technology has not changed much in 50 years because the tone still can’t be beat. This is not all good news as 50 year old technology comes with quirks such as tube rattle.

I was playing through my Marhsall DSL 401 amp and started to notice an unpleasant background tone occurring on certain notes after the amp had warmed up. It was a metallic rattling/squeaky sound; like when the wheel bearing started going out on my ’66 Plymouth Fury. I could understand something being loose inside amp but the rattling was amplified!

I now know an amp tech and he had me bring it on over for a listen and he said "Oh, that sound?" “Yep!” I say with a dawning realization that this was going to turn out to be one of those obvious things everyone knows but me. “Tube Rattle” he says.

If a vacuum tube starts going microphonic (certain frequencies cause it to vibrate internally) the sound will be amplified through the system. The amp tech opened the back panel and tapped on each of the preamp tubes. Sure enough, once he reached the second one it reproduced the exact sound. A couple of new preamp tubes later (if replacing power tubes replace all at once with a matched set) the irritating sound is gone.

If your tube amp starts to issue a metallic rattling effect it may not be your playing or your wireless access point or your power outlet grounding or your effects pedals.... [oops, gave away some of the rookie things I checked]. Just do the tap test (observing caution of course, don’t dig around inside the guts of your amp, use a pencil to do the tapping) and enjoy your pure tube tone!

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