Fender Super Champ XD Geiger Counter

[PatrickTeaneck]

I have been loving my new-to-me Super Champ XD, but while I was playing it a couple nights ago with my Tele, from out of nowhere it just started making a very loud crackling sound, like a geiger counter. Volume knob didn't change volume of sound, makes sound with or without guitar cable plugged in. The only things I could find online about this sound suggested it was a cell phone or some kind of interference, like a florescent light. It's not either of these things. It's very loud. I have only turned the amp on one other time since to record the sound, because I was worried I might cause further damage. Any ideas? It has fairly new JJ tubes with low milage. I tried to attach an mp3 file but forum doesn't seem to allow it. Thanks!

 

[Jbnaxx]

I have the SCXD. It is not unusual for mine to make some crackling sounds when I first turn it on. Mine usually clears up when it gets warmed up.

You might try to put in some tubes if you have some laying around. There are some knowledgeable folks on here that might be more help.

 

[PatrickTeaneck]

I have the SCXD. It is not unusual for mine to make some crackling sounds when I first turn it on. Mine usually clears up when it gets warmed up.

You might try to put in some tubes if you have some laying around. There are some knowledgeable folks on here that might be more help.

This went from dead quiet to full volume crackling. When I had the problem you mention with other amps, usually the volume knob can control it. But I did have one that would whine and pop for about 1 minute, then it was great. That was a Crate vfx 5212

 

[tubeToaster]

Sounds like a bad solder joint. You can poke around with a chop stick with the amp on and possibly find the bad joint. But if you are not familiar with the inner workings of a tube amp you should take it to a tech. There is 350+ volts in there.

 

[JL_LI]

I retired my SCXD years ago so I'm going from memory here. I believe that the volume control is really gain with the amp operating as if a volume control was set to max. If the crackling doesn't change as rotate the volume dial, you may have be a power tube problem. Replace it, especially if the amp is "new to you". You have no way of knowing how the amp was maintained before you bought it. Board level failures usually result in a complete failure. Cold solder joints sometimes begin to work when the amp heats up and metals expand. Your problem doesn't strike me as either of those. Good luck. I always hate it when something inexplicably stops working.

 

[Blue Bill]

90% of problems like this in a tube amp are due to tubes going flooey. Try switching the preamp tube with a new one, here's a good chance the problem will be gone. The other thing to check is your guitar output jack and cable. These can get crackly from being moved around. Solder joints, generally speaking, don't fail, sitting still, without being physically knocked around.

 

[Jbnaxx]

I’m not an amp tech... but if the volume had no effect couldn’t still be an output tube?

 

[PatrickTeaneck]

90% of problems like this in a tube amp are due to tubes going flooey. Try switching the preamp tube with a new one, here's a good chance the problem will be gone. The other thing to check is your guitar output jack and cable. These can get crackly from being moved around. Solder joints, generally speaking, don't fail, sitting still, without being physically knocked around.

I tried it again this morning on another power outlet in another room. Same issue, but now I notice some fireworks going on inside one of the power tubes. I am going to replace that tube. Do I need to get a matched pair of 6V6's for this model? Or can I just replace one?

 

[Randypttt]

Is there a Ham Radio guy/gal in your neighborhood close by? Maybe practicing their Morse code?

Had a couple retirees living next to me with a Ham radio. Every once in awhile they would broadcast something that ripped through my stereo speakers. Annoying

Just a thought

 

[PatrickTeaneck]

I retired my SCXD years ago so I'm going from memory here. I believe that the volume control is really gain with the amp operating as if a volume control was set to max. If the crackling doesn't change as rotate the volume dial, you may have be a power tube problem. Replace it, especially if the amp is "new to you". You have no way of knowing how the amp was maintained before you bought it. Board level failures usually result in a complete failure. Cold solder joints sometimes begin to work when the amp heats up and metals expand. Your problem doesn't strike me as either of those. Good luck. I always hate it when something inexplicably stops working.

Me too! I am a fairly new guitarist, and just dipping my toe into the tube amp world. I love the sounds I get, but they seem to be pretty finicky! I just bought a '74 Pro Reverb for $270 because when I went to try it out, it was making a deafening rattling noise. Neither the seller nor I knew what it was and I low balled, hoping it was not going to be an expensive fix. Brought it home and it's quiet as a mouse!

 

[archetype]

I tried it again this morning on another power outlet in another room. Same issue, but now I notice some fireworks going on inside one of the power tubes. I am going to replace that tube. Do I need to get a matched pair of 6V6's for this model? Or can I just replace one?

The Long Answer:

If there are fireworks, shut it off and don't turn it on until you replace both power tubes and set the bias. You don't want one of them to short internally and maybe take other components along for the ride. Be disciplined and shut it off.

A matched set of 6V6-GT or GTA is best. We spent a few decades shoving whatever tubes we had into our amps and generally were lucky, but matching prevents a pair from having wildly differing current draws and one of them redplating while the other is fine. The SCXD has a single source of bias voltage that's the sum of the voltage for both tubes. You can't bias individually, at least without replacing a fixed resistor, so a matched pair is best. You will need to check and set the bias voltage. If you're comfortable working in a chassis with LETHAL VOLTAGE that's live, then you can set the bias with a multimeter. If not, take it to a tech. The Fender spec for the sum of the two tubes is 40 mV. Old stock tubes from the US, EU, UK, and Japan can take 45-50 mV, usually. Bias by ear between 40 and 50 mV and set it where it sounds good to you. A JJ 6V6S set can take 45-50 mV. They're a bit more defined and bright than a 6V6-GT.

A used, matched set that tests good, from a proper tube dealer, will likely last for the life of the amp if it isn't gigged. NOS is fine, as well. If you're looking to save some money, you can get a mixed, matched set as long as they match well. Example: A GE 6V6-GT with a top-getter can coexist with an RCA (rebranded "Conn Organ") 6V6-GT with a side-getter.

Current production tubes? Some are good and some are crap. There are some reilable sources that test and weed out the crap and you'll pay a bit of a premium for that service. My experience is that NOS or used OS last longer, often sound better and I'll pay the price for that.

Here are reliable dealers I've bought from multiple times. There are other, good dealers. I've listed my tube choices, per my experience with blasting an SCX2 (same circuit as yours) pretty loud. There are subtle differences at both low and high volumes, but all will sound good.

KCA Nos Tubes
The owner is a member over on Strat-Talk. From their 6V6 page,

GE 6V6-GTA. $95.00 for a matched pair. Good all-around tube.

Philips JAN 6V6-GT. $84.00 matched pair. Military tube. Stays a bit more defined when cranked. A good price.

Sylvania JAN 6V6-GT. $95.00 matched pair. Military tube. Stays a bit more defined when cranked. Basically the same tube as the Philips, so I'd get the Philips because of the lower price.


Audio Tubes
The owner is Brent Jessee. It's best to order over the phone. Prices tend to be a bit better on the non-holy-grail tubes than KCA pricing. The 6V6 page.

6V6GTY JAN military type brownbase, all USA made brands. $70.00 for a matched pair. Mixed brands and/or markings. That's not a problem.

6V6GT General Electric. $50.00 for a matched pair. Relabled with multiple brands. Good all-around tubes.

6V6GT Sylvania blackplate 1950s greyglass or clearglass. $70.00 for a matched pair. A bit brighter.

6V6GTA RCA clearglass. $80.00 for a matched pair.

The Short Answer:

If there are fireworks, shut it off and don't turn it on until you replace both power tubes and set the bias. You don't want one of them to short internally and maybe take other components along for the ride. Be disciplined and shut it off.

Take it to an amp tech.

By The Way:

Get an inexpensive NOS or used OS 12AX7. You might as well put it in to replace the OEM tube the amp came with. Save the one you take out.

 

[PatrickTeaneck]

The Long Answer:

If there are fireworks, shut it off and don't turn it on until you replace both power tubes and set the bias. You don't want one of them to short internally and maybe take other components along for the ride. Be disciplined and shut it off.

A matched set of 6V6-GT or GTA is best. We spent a few decades shoving whatever tubes we had into our amps and generally were lucky, but matching prevents a pair from having wildly differing current draws and one of them redplating while the other is fine. The SCXD has a single source of bias voltage that's the sum of the voltage for both tubes. You can't bias individually, at least without replacing a fixed resistor, so a matched pair is best. You will need to check and set the bias voltage. If you're comfortable working in a chassis with LETHAL VOLTAGE that's live, then you can set the bias with a multimeter. If not, take it to a tech. The Fender spec for the sum of the two tubes is 40 mV. Old stock tubes from the US, EU, UK, and Japan can take 45-50 mV, usually. Bias by ear between 40 and 50 mV and set it where it sounds good to you. A JJ 6V6S set can take 45-50 mV. They're a bit more defined and bright than a 6V6-GT.

A used, matched set that tests good, from a proper tube dealer, will likely last for the life of the amp if it isn't gigged. NOS is fine, as well. If you're looking to save some money, you can get a mixed, matched set as long as they match well. Example: A GE 6V6-GT with a top-getter can coexist with an RCA (rebranded "Conn Organ") 6V6-GT with a side-getter.

Current production tubes? Some are good and some are crap. There are some reilable sources that test and weed out the crap and you'll pay a bit of a premium for that service. My experience is that NOS or used OS last longer, often sound better and I'll pay the price for that.

Here are reliable dealers I've bought from multiple times. There are other, good dealers. I've listed my tube choices, per my experience with blasting an SCX2 (same circuit as yours) pretty loud. There are subtle differences at both low and high volumes, but all will sound good.

KCA Nos Tubes
The owner is a member over on Strat-Talk. From their 6V6 page,

GE 6V6-GTA. $95.00 for a matched pair. Good all-around tube.

Philips JAN 6V6-GT. $84.00 matched pair. Military tube. Stays a bit more defined when cranked. A good price.

Sylvania JAN 6V6-GT. $95.00 matched pair. Military tube. Stays a bit more defined when cranked. Basically the same tube as the Philips, so I'd get the Philips because of the lower price.


Audio Tubes
The owner is Brent Jessee. It's best to order over the phone. Prices tend to be a bit better on the non-holy-grail tubes than KCA pricing. The 6V6 page.

6V6GTY JAN military type brownbase, all USA made brands. $70.00 for a matched pair. Mixed brands and/or markings. That's not a problem.

6V6GT General Electric. $50.00 for a matched pair. Relabled with multiple brands. Good all-around tubes.

6V6GT Sylvania blackplate 1950s greyglass or clearglass. $70.00 for a matched pair. A bit brighter.

6V6GTA RCA clearglass. $80.00 for a matched pair.

The Short Answer:

If there are fireworks, shut it off and don't turn it on until you replace both power tubes and set the bias. You don't want one of them to short internally and maybe take other components along for the ride. Be disciplined and shut it off.

Take it to an amp tech.

By The Way:

Get an inexpensive NOS or used OS 12AX7. You might as well put it in to replace the OEM tube the amp came with. Save the one you take out.

thanks for the knowledge! Before I read this I took it to my local guitar shop and they put a used Russian tube in. (Sovtek?) Cost $15. He said it shouldn't matter than they aren't matched. I will check out the pages you recommended though. I just wanted to confirm it was a tube issue and not something else. And yes, I immediately shut it off when I heard the sound. Only flipped on a couple times after that to demonstrate it to someone.

 

[Willie Johnson]

Is there a Ham Radio guy/gal in your neighborhood close by? Maybe practicing their Morse code?

Had a couple retirees living next to me with a Ham radio. Every once in awhile they would broadcast something that ripped through my stereo speakers. Annoying

Just a thought

I was getting British-accented religious programming through my Champion 600 around Christmas. Or maybe OP's neighborhood soup enthusiasts are running their electric can opener at the same time?

 

[Blue Bill]

I tried it again this morning on another power outlet in another room. Same issue, but now I notice some fireworks going on inside one of the power tubes. I am going to replace that tube. Do I need to get a matched pair of 6V6's for this model? Or can I just replace one?

Mis-matched tubes usually works fine. Sometimes, the mismatch causes the amp to sound slightly different, but it's unpredictable; the only way to tell is to try them out. Good luck, I love my SCXD!