Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jeff on December 29, 2010, 08:47:56 pm
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Is there a problem with placing a tube too close to the speakers magnetic field? I built a little 6V6 combo amp and the tube wound up right behind the speaker magnet, pretty close. When I play real loud I can hear a wierd sound. I tried 3-4 diffrent 6V6's but it happens on all of them. It doesn't happen when the amp is out of the cabinet.
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Describe said sound.
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It's a rattly sound. It seems to jump out more at certian pitches. I first thought it was because it's a combo. It does not do this with the chassis out of the cab. I tried everything I could think of to dampen vibrations. rubber rings on tube, rubber mounted socket, rubber mounted chassis. I thought I had a "rattly" tube but it does it with every tube I've tried (3-4). I know they make combos so I was just wondering if the problem is the tube is too close to the speaker. Could the electrons flowing through the tube be influnced by the magnet.
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Jeff,
Do you have another speaker cabinet you can set it on? Disconnect your internal speaker and run it to your extension. If the vibrations still cause the noise it may be ALL the tubes have a problem. Are they from the same order/lot? If the noise goes away, you may need to build a bigger combo cabinet! How close are we talking? Is this a new transformer? Or, what if you set the chassis on top of your combo cabinet (using your combo speaker). What happens then?
Jim
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Ah transformer, didn't think of that. The tubes are all different brands NOS RCA, Jan Phillip, Electroharmonix and I did try different 12AX7's too. The 6V6 is right behind the speaker magnet.
I'll try setting it on top of the cab and see what happens. Thanks.