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Post subject: Superchamp XD "static"
Posted: Thu Jan 05, 2012 4:06 pm
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I am a newbie to this list, and a student level player. Been playing for maybe 4 years.

Apologies of this has been covered elsewhere. I did a search on super champ XD, and read as much as I could stand, but am having trouble with much of the terminology (tube rattle? (wtf?)), so a solution may have been described and I just don't get it.

The superchamp XD is my first/only amp.

As the topic/subject line indicates, I am getting what I can best describe as "static" when playing either channel of this amp now. It started a couple days ago. I have tightened up the speaker, and all other screws I can find. Have removed and re-seated the tubes. All to no avail. I may not be describing it correctly, but "static" is what it sounds like.

Any help?


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Post subject: Re: Superchamp XD "static"
Posted: Fri Jan 06, 2012 9:59 am
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If you mean a kind of am radio static in a storm sound, it's very possibly a tube problem, esp. if you've had the amp for 4 years. Take a pencil & lightly tap on the tubes w/the eraser end. If the crackling gets worse as you tap, you'll need to replace the tube or tubes. If it's the 12ax7 you can get by w/just replacing that. If it's one of the power tubes, you'll need to replace both w/a matched pair, & rebias. Or better yet, replace all 3. If you don't know how to bias, you should take it to an amp tech. It could be some other problem, but this test will tell you if it's a tube. BTW are you unplugging the amp when you are touching the tubes? There's a danger of shock while the amp is plugged in. Please be careful :!: If you want more info, try searching for tube problems in general, not specifically for the SCXD. All tube amps have these kind of problems. good luck


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Post subject: Re: Superchamp XD "static"
Posted: Fri Jan 06, 2012 10:55 am
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You may want to also try contact cleaner. Spray a SMALL amount into the sockets and input jack, any EFX jacks, and the speaker output. I like Caig Deoxit GN5 Gold. It's rated to a higher temp than the plain red Caig D5.

BTW... this product works well for "scratchy" pots, too.

Good luck!


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Post subject: Re: Superchamp XD "static"
Posted: Fri Jan 06, 2012 7:56 pm
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Mojjett, you are describing what I am hearing perfectly. It is an AM Radio static kind of a sound. I haven't tried tapping on the tubes, but tapping lightly on the cabinet increaes the static, and it follows the tapping - if you get what I am saying.

So maybe I'll replace all 3 tubes. I don't know how to rebias, but I have read about it. I need to see if there is a tech in my area, or learn how to do it myself. Do you (or does anyone) know if there are any online DIY guides for rebiasing?

Also not tapping tubes with power on. Me very scared of elec shock.

Will also try the contact cleaner thing, I probably need to pull a mahor PM on the amp. have had it for awhile....


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Post subject: Re: Superchamp XD "static"
Posted: Fri Jan 06, 2012 9:09 pm
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Pulling tubes and spraying contact cleaner usually solves a lot of crackling, scratchy, static sounds. Really... that been my experience. Even with brand new tools (like a Dremel) that turn on-&-off on its own. Contact cleaner where it contacts to the battery solved that issue. It's worth a try.

If that doesn't work. And you decide to try new tubes. Rule-of-thumb is the gain stage 9-pin miniature tubes DO NOT require re-biasing (the tubes usually under aluminum covers). Only the output power tubes need bias adjustment. Whether you replace the output tubes or the rectifier tube, if the amp has one.


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Post subject: Re: Superchamp XD "static"
Posted: Sat Jan 07, 2012 12:28 am
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sdoolin, To be certain, I would try the test as I described w/a pencil directly on the tubes. For this, the amp needs to be turned on. It's safe enough as long as you don't try handling the tubes w/the power on & the amp plugged in. It does sound to me that's where the problem is. I had the exact same symptom w/my DRRI. 1st time was 2 of the 12ax7s. When I tapped on them, they gave a kind of ringing sound (harmonic). Then I replaced all the tubes w/JJs & one of the new power tubes was bad. And that gave a popping sound when I tapped on that. In both cases the amp was crackling when it was on. By all means, try the contact cleaner first. Maybe you'll save some $$. As far as biasing, there are tutorials on the internet. That's how I did mine. IMO it's something worth knowing. Just google "tube biasing". The better (safer) way is w/a pair of bias probes, & a multi meter. Just be sure you thoroughly read up first. There's some good youtube vids as well. Maybe you can find one specifically for the SCXD. cheers


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Post subject: Re: Superchamp XD "static"
Posted: Sat Jan 07, 2012 6:56 am
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Thanks for the tips. I am going to try both contact cleaner and tube tapping later today, will read up on tube biasing, seems like something I need to know how to do.

Traveling next week, so will let y'all know how it goes later.


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Post subject: Re: Superchamp XD "static"
Posted: Sat Jan 07, 2012 7:55 am
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Sdoolin,
take your amp to the dealer and see if they will let you check out some new tubes. If you still have a mom and pop shop in your area ( please support mom and pop music shops :-), most of them will be happy to help you and probably have a set of good tubes that you can test. Good luck!


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Post subject: Re: Superchamp XD "static"
Posted: Sat Jan 07, 2012 8:09 am
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There is a "mom & pop" locally. That is where I bought the amp. I coulda bought it o nline, but I do like to support local businesses. I just haven't had much luck with them on other items. They are staffed by some really smart folks, but they like to tell you how smart they are.

I'm gonna try to do this on my own (with help from the forum obviously).


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Post subject: Re: Superchamp XD "static"
Posted: Sun Jan 15, 2012 11:56 am
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OK, finally back to work on this again. Tapping on the two larger tubes with a pencil eraser (very very lightly) does produce the "static" noise. So from what y'all say hear, that means replacing those 2 tubes, and re-biasing. I am up for that. I suppose I should replace all three tubes while I am at it?

I'd really like to keep this amp working. I have ordered a new amp from another mfg, but I'd like to keep this SCXD around. It is versatile, and I can keep one amp for indoor (quiet) practice, and another (my new one) out in my barn/shop/studio for making real noise.

As always all help appreciated, I am gonna shop around for tubes....


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Post subject: Re: Superchamp XD "static"
Posted: Sat Jan 21, 2012 10:58 am
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Quick update for anyone that cares. I purcahsed all 3 tubes from thetubestore.com. That is 2 of the 6V6's and a single 12AX7. The power tubes are Tung-Sol "GT". I ordered them as a "matched set", and they showed up very quickly, both power tubes marked with a "20" on the box.

I read up on biasing them (there is a thread on this site with seemingly exact instructions for the SCXD), but I couldn't quite sort that out. Something about reading 40 mV at pin 8. I either don't know how to read my multi-meter (which is VERY possible), or it doesn't read mV. Also says to adjust bias with the blue "knob" on the circuit board. I see the blue knob, but am unsure if I adjust that for one, or both tubes? I am going to try again with biasing them, will read up some more.

For now, everything back to normal with my SCXD, and it sounds great. Sounds better actually.


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