Do you think my Super Champ XD can be resurrected?

[Mr Perch]

My SCXD just up and quit on me. I was playing along peacefully at low volume, and the sound just stopped. I examined it; it appears that all three tubes are glowing. The speaker is plugged in tightly. Changing guitar cords had no effect. I tried running a line out to my power amp -- nothing there. Both channels, same problem. The red light on the console that indicates that channel 2 is on no longer works, either when I press the little console button or from the footswitch (although the footswitch light goes on.) I'm thinking that I just lost the modeling and effects chip. Any suggestions?

[celeste]

The SCXD is well known for failure of the DSP board, that is pretty much the whole preamp. Under warranty the fix is an amp replacement, it was not worth trying to fix the small signal portion of the amp. I don't know or anyone and have not heard of anyone being successful repairing the front end of those amps.

If I could get one or some cheap, I would like to try some conversions away from the digital front end

[kleuck]

One fun thing is that tube amps are often described as "fragile"...by people who did not ever owned one i suppose.

[telex76]

Another one bites the dust.

[AirBagTester]

I hope mine doesn't bust... if it does I guess I still have a 1x10 speaker cabinet to use though.

[JimInMO]

Somewhere around these forums are detailed instructions, with photos, for a line in mod. I think the premise was to have an effects loop. With a line in and a multi fx unit from Line6, Zoom or Digitech you would still have a nice tube power amp. I think it was originally posted on the Agile forum but I couldn't find it with a search.

[celeste]

Originally Posted by JimInMO

Somewhere around these forums are detailed instructions, with photos, for a line in mod. I think the premise was to have an effects loop. With a line in and a multi fx unit from Line6, Zoom or Digitech you would still have a nice tube power amp. I think it was originally posted on the Agile forum but I couldn't find it with a search.

Yeah, that would be an excellent way to go, separate outboard pre, just use it as a power amp speaker combo.

[Gnobuddy]

Originally Posted by celeste

Yeah, that would be an excellent way to go, separate outboard pre, just use it as a power amp speaker combo.

I agree, I made exactly the same suggestion on a different thread (SCXD owners club thread).

It would also be worth experimenting with the feedback resistor - Fender put in lots of negative feedback in the tube power amp section of the SCXD to make it extremely clean, as all the distortion is supposed to come from the DSP front-end. Increasing that resistor will most likely make the tube power amp sound more "tubey".

-Gnobuddy

[Mr Perch]

Gnobuddy, do you live anywhere near Glendale? I might make my deceased amp available to you as a guinea pig.

[keithb7]

Sounds to me like a great opportunity to build a tube amp from the chassis. cabinet and speaker!

[printer2]

I would not mind coming across a fried XD, doubt it will happen any time soon. Not like this link will help me though.

http://www.thegearpage.net/board/sho...php?p=12192203



http://support.fender.com/schematics..._schematic.pdf

I would change R5 to 1M. Actually isf you take the signal after the second IC and feed a tone stack you could probably then send it to the power amp section. Maybe even into IC-3 then if the analog stuff is working and the digital is not.

[Gnobuddy]

Originally Posted by Mr Perch

Gnobuddy, do you live anywhere near Glendale? I might make my deceased amp available to you as a guinea pig.

Mr Perch, thanks for the offer; I do indeed live not far from Glendale (maybe 15 minutes on the freeway in good traffic). I would not feel right taking that amp off your hands for nothing, but I'll contact you by PM and we can discuss this further...it would be cool if I can bring that amp back to life and get it back to you, no? :)

-Gnobuddy

[Gnobuddy]

Originally Posted by kleuck

One fun thing is that tube amps are often described as "fragile"...by people who did not ever owned one i suppose.

Tubes and transistors are fragile in different ways.

Tubes are much more robust when it comes to momentary electrical overload. You can overload a tube till it "red plates", and if you then cut the power and fix the problem that caused the overload, chances are the tube will be fine.

Transistors and their relatives, on the other hand, die virtually instantly if electrically overloaded. Poof. Gone. Dead.

But when it comes to physical overload - shock and vibration - tubes are fragile and transistors are tough. Drop a tube ten feet down onto concrete and we all know what happens. Drop a transistor the same way and it won't even notice it. They make solid-state circuitry that is built into cannon shells and fired from big naval cannons - and it survives even those incredible accelerations. It's not hard to guess how a vacuum tube would fare under those circumstances.

Overall, there is no contest; solid-state circuits are far, far, far more reliable. The computer I'm typing this on has something like a billion MOSFET's in it altogether (between the CPU and the graphics card), and every one of them has to work to keep the machine running. It's been working flawlessly for years now, and continues to do so.

By contrast, back in the early days of computing, US engineers built computers with several thousand vacuum tubes in them. Those computers would die every few days because one of those thousands of tubes had failed and needed to be replaced.

So the devices in the modern solid-state computer are literally more than a million times more reliable than those vacuum tubes, since the modern PC contains a million times more MOSFETs and still doesn't die every few days.

Unfortunately, reliable and efficient though they are, solid state devices still don't sound as good in a guitar amp as ancient, fragile, obsolete vacuum tubes do. That's the only logical reason why ancient tube technology continues to be popular with us electric guitarists.

Just to be clear, I love tube guitar amps!

-Gnobuddy

[kleuck]

Practically speaking, that is all false when it comes to Guitar amps, i never saw a dead tube amp -and BTW i do not drop my tubes but i am not a gentle guy with amps, i saw tons of dead transistor amp on the contrary.
Tubes fragile ?
Yeah, cannons, jets and radars need transistors, actually, WWII did not happen due to the lack of suitable technology at the time 5881 were not designed for landing gear servomotor control, no tube in a MIG25...
Know what ? I own a Mazda 12AX7SH "AIR", witch was used in the French Mirage.
Do you know why tube did not entirely disappear during the 80's ?
Because of their military use : they can stand an EMP where transistors can't without a huge shielding.
And...just drop your computer from ten feet down onto concrete just to know what happens.

[printer2]

You guys, quit dropping your equipment! It is making me cringe.

[Mr Perch]

Originally Posted by kleuck

Do you know why tube did not entirely disappear during the 80's ?
Because of their military use : they can stand an EMP where transistors can't without a huge shielding.

A Soviet MIG pilot defected and landed his plane in Japan. US intelligence analysts dissected it and were puzzled to find tubes instead of transistors, until they realized that with tubes, the electronics in the plane would continue to work under conditions of nuclear war. Presumably the pilot also played through a tube amp for the same reason.

[AirBagTester]

Originally Posted by Mr Perch

A Soviet MIG pilot defected and landed his plane in Japan. US intelligence analysts dissected it and were puzzled to find tubes instead of transistors, until they realized that with tubes, the electronics in the plane would continue to work under conditions of nuclear war. Presumably the pilot also played through a tube amp for the same reason.

Yeah, but then the pilot has to steer with his knees while he's playing it.

[Gnobuddy]

Originally Posted by kleuck

Practically speaking, that is all false when it comes to Guitar amps

Come on, my friend, the tubes in a guitar amp are no different than any other tube, and subject to the same physics. They are basically modified light bulbs, and that means there are delicate filaments and delicate mechanical structures inside them. The filaments run colder than a light bulb, so they last much longer, but they are still delicate glass bulbs filled with delicate mechanical structures.

That's why some tubes are microphonic - the internal mechanical bits are delicate and not 100% stiff, so they can move a little bit under the influence of external vibrations, causing the microphonic behaviour.

Ever seen a microphonic transistor?

Originally Posted by kleuck

I never saw a dead tube amp

Ask any tube amp technician. He (or she) sees dead tube amps every day, and makes a living fixing them!

Originally Posted by kleuck

I saw tons of dead transistor amp on the contrary.

Yes, transistors die too, especially when overloaded. In the early days of transistors (1960's and 1970's) they were extremely unreliable, like every new technology is at first. Today they are extremely reliable. Of course no technology is ever 100% reliable.

However today your life is full of solid-state electronics containing literally millions of transistors (MOSFETs) - your phone, your computer(s), your TV, your home-theatre amplifier, the smoke-detectors and fire alarms in your house, your remote controls, your digital camera, your mp3 player, and on and on and on. Your car contains millions of MOSFET's too, in the dozens of little computers that control the fuel injection, the transmission, the traction control system, and who knows what else. If you bought a good brand, chances are all of these solid-state devices are extremely, extremely reliable.

How about solid state amps for musicians, even guitars? Sure! The vast majority of bass guitar players use solid state amps. The vast majority of live "acoustic" guitar players use solid state amps to amplify their onboard pickups. Any band that uses a P.A. today is using solid state amps. You use monitor speakers when playing live? They're driven by solid-state amps. How about the keyboard player? She (or he) is using a solid state keyboard amp. The vocalists? Solid state amplification.

In fact today solid state amps have replaced tube amps for every purpose except amps for electric guitars, and a tiny handful of audiophile home stereo amps. The simple fact is that solid state amps are better than tubes at just about every amplification job except amplifying certain types of electric guitars in certain types of music. In those few areas, nobody has yet come up with an affordable solid state amp that sounds as good as a good tube amp.

I have no emotional investment in either tubes or solid-state devices. Both are fascinating bits of human technology, both are the result of centuries of slowly accumulating enough scientific knowledge to control electrons, both have served humanity well. Whichever one works better, that's the logical one to use for that function.

Originally Posted by kleuck

Yeah, cannons, jets and radars need transistors, actually, WWII did not happen due to the lack of suitable technology at the time

Sure, tubes served humanity well - more than half a century ago. Why do you suppose the armed forces don't use tubes in their newest jet fighters and tanks and ships? Why doesn't Airbus and Boeing and Douglas fill their current airliners with vacuum tubes? Why is the medical electronics in the hospital emergency room not built with vacuum tubes? Lives depend on these things working, if tubes are more reliable than transistors, why aren't tubes being used?

Originally Posted by kleuck

Do you know why tube did not entirely disappear during the 80's ?
Because of their military use : they can stand an EMP where transistors can't without a huge shielding.

Yes, I knew that. As I said, tubes and transistors are fragile in different ways. Tubes can handle huge electrical overloads and nuclear EMP better than transistors can. It's a fact.

Originally Posted by kleuck

And...just drop your computer from ten feet down onto concrete just to know what happens.

You know what? I have repaired computers for many of my friends, and I have actually seen computer which were dropped on the floor (usually fell off a desk).

When this happens, mechanical parts may fail. Sometimes the hard-drive dies. Sometimes the weight of the heat-sink damages the motherboard (circuit board).

But the solid state devices - the CPU, the memory, the chips on the mother board and graphics card - they are never hurt in the slightest by the fall!

So go ahead and drop your computer ten feet onto concrete - you won't damage any of the solid state devices! (But you will probably damage the case, destroy the hard drives, tear up the motherboard, and do other expensive damage!)

I can see that you love tubes, and I respect that; they are wonderful things that took us into the age of electronics, and they still serve us guitarists well. I love them too. But my love isn't blind - I can see that they have flaws as well as virtues, like every other technology.

-Gnobuddy

[printer2]

Yeah. but nothing keeps ticking like pneumatics.

[Gnobuddy]

Originally Posted by printer2

Yeah. but nothing keeps ticking like pneumatics.

Hydraulics are pretty good too. I have one of those hydraulic gizmos beating away inside my chest. It's been working nonstop for around four and a half decades now, with zero maintainence. And yes, it's been dropped on the floor a few times over the years, along with the rest of me!

Did you know hydraulic and/or pneumatic circuits have actually been used to perform the same functions as electronic circuits? This field of engineering is called Fluidics.

-Gnobuddy