Do I hear tube rattle or what?

[emisilly]

Yesterday I put a new speaker in my Ampeg Jet reissue. Well, its a pretty small cabinet, and the new speaker is actually just making contact w/ the chassis. The EL-84's are also sticking out of the bottom of the chassis about 1/2 inch from where the contact is. I noticed when I played low notes with the neck pickup (bassy) that I could hear a rattling sound coming from the speaker. With the bridge p/up there was zero noise. With the middle selected, only a tiny bit, and it wasn't always present. It didn't sound like the reverb springs, it was more "tinny". Am I hearing the power tube fillaments rattling? The tubes are mounted with a very solid and strong retainer, but I doubt this does anything to reduce vibration.

I did notice that when I brought the amp to my house later that day that the sound couldn't be heard. In fact, it sounded fantastic. I only heard it at my office, where the electrical system is pretty old and has caused my tube amps to sound funky at times (pops and general quirkiness I couldn't hear at home or elsewhere).

Just want to make sure I'm not killing my tubes and setting myself for a sudden failure when I least want or expect it.

[sixty4fairlane]

no worries, mate. Sometimes goofy things like that happen.

[Telecluster]

here's an excerpt from another post i did about testing for tube ratttle or "microphonic" tubes ---hope it helps

3) Check for microphonic tubes For smaller pre-amp and/or phase inverter tubes like 12ax7 or 12at7, I use just a plain old thin lead mechanical pencil like a .05 mm lead extended about an inch or 1.5 inches (you would have a hell of a time writing with it that way without breaking the lead, but is perfect for checking small tubes) Tap gently on each of the tubes while the amp is turned on at a good volume, but without a guitar or anything else plugged into it. As you GENTLY tap, you should hear nothing more than just a very gentle hint of a tap thru the speaker. Especially listen for the kind of rattle or jingle that you are trying to chase down. For larger tubes like 6l6 or EL34 use something larger like the sharpened tip of a regular wood pencil (be sure it's a #2 if you have Scan-Tron tubes) some people like to use wood chinese food chopsticks to tap on tubes. (season the tubes accordingly with MSG, ginger root or sea urchin paste)--------ANYWAY---- Listen for any rattles or jingles THROUGH THE SPEAKER. If they seem to match the bad sound that you are trying to chase down, then it is a very good bet to change out the tube that responds badly to your tapping.

4) It helps to compare the tap response between LIKE tubes within any given amp because ALL TUBES have AT LEAST SOME microphonic properties(and that's a BIG part of what gives them character). What I always listen for is something that stands out like a sore thumb on any given tube among a jury of its peers.

5) save up all your rattling and jingling microphonic tubes that you acquire over the years and start a percussion band in which the musicians all stand BEHIND the amplifiers and tap away at all of thier microphonic tubes with pencils and chopsticks.

Hope you get your Shake Rattle and Roll shaking rattling and rolling in a way that is sonically pleasant to ya!
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[emisilly]

Well, I checked for microphonics ( thanks for the advice!)....none to be heard there. Played some more, at home, and the sound came back. Switched speakers, sound came back. I made every single screw as tight as could be and searched in the chassis and on the board for anything loose...nothing. Now, I know EL-84's can get kind of noisy/rattly in a small cabinet combo, but I've had a couple of Blues Jr's and never heard this. I'm guessing the power tubes just may be going bad? This is a pretty fair assumption since after the amp is on for about 15 minutes notes start to get a little fuzzy and semi-overdriven in a non-musical way, even at low volumes. Once she cools off and is fired up again the fuzz isn't there, until you play for another 15 minutes and there it is.

[zook]

The power tuibes aren't going bad, some EL84s rattle in the bottle, it's an unfortunate fact about them. Try a couple others to see if you can find quieter ones.

Winnie

[Telecluster]

Well, it's almost certainly a problem directly related to heat. A good way to test for components in your amp (capacitors, resistors) that might be MARGINAL at cool temps but thrown over the line once the heat from the tube filiments makes it's way to them is to simply put an ordinary portable house fan behind the amp and see if you get more than the 15 minutes that you described out of the amp before it sounds fuzzy. audio tubes with anomalies usually have problems as soon as they reach operating temp (only about 1 or 2 or maybe three minutes, but not 15 minutes). I am not familier with the Ampeg you are describing, but if it has a tube rectifier, (not to be confused with a tube inverter) then It could possibly be a power tube---It ALSO could be another component after getting heated up by the tubes---Try the fan test. If nothing else, It's always nice to play to an audience of your fans. I'm not suggesting this as a permanent fix, just a diagnostic aid.

[brendan780]

Originally Posted by sixty4fairlane

no worries, mate. Sometimes goofy things like that happen.

ha shreveport eh? me too well.. benton