Fender Champion 600 Problem

[Michael070]

Hi everyone, anyone. I am new to the forum and to tube amplifiers, which will all be evident in about 13 seconds. I recently picked up a champion 600, secondhand, and had read about the modifications and upgrades online. I like to , I believe the scientific term is "fidget," with such things but normally, only within my comfort range. I figured I was addressing the easiest of any of the modifications when I replaced the 12ax7 and the 6v6 and upgraded to the weber speaker. I'm not a moron, I've been and in around guitars and amps for over 25 years just never took to messing with the amps I owned and mainly stayed on the acoustic side of the fence anyway. Anyhow, I backed out the 12ax7 and replaced with a 12ax7, I backed out the 6v6 and replaced it with a 6v6 and then I backed out the fender speaker and replaced it with the weber speaker. I didn't get a chance to immediately try it out but when I did come back to it two days later, I plugged it in, I lit it up, and ...nothing. Jewel lights up, 12ax7 lights up, 6v6 lights up but no sound. I can hear in the speaker that the amp is on but no fluctuation when I adjust the volume. I plugged the speaker into an outside source and it plays. I checked the fuse and it's good. I called the local amp repair shop to feel him out for a clue but of course he was swamped and all I could get out of him, after I explained what had happened, was "sounds like it's in the preamp," but they're 3 weeks backed up and at $65.00 to troubleshoot and $65 an hour, which I can't imagine would take any time for someone with experience to take this thing apart and put it back together, but still, I don't want to keep dishing out money when I could just go buy another one. So screw all that, I want this one. I've looked over the board and the schematics but transistors and cathodes and resistors, I have no idea what that means. But I do know what R11 and R12 mean and I know how to solder and I know not to go stabbing a soldering iron or screw driver into the back of the amp to kill myself, they'll be plenty of time for that at the end. So if there's anyone out there who can kindergarten walk me through the troubleshooting process, that would be lovely. Oh, and also, the first thing I did after there was no sound was back everything out and put all the stock pieces back in place and got the same result. I checked my guitars and my cables and they all work fine on other amps. I purchased and wired a new volume pot, figuring that is starting at square 1 but I really don't know where to go from here. ANY HELP would be greatly appreciated. Thanks in advance!

[eschertron]

Hi Michael, welcome to the place!

I picked up a Fender Champion 600 a few years ago, and have had great fun tweaking and playing it. It is an excellent choice for trying your hand at this kind kind of modding.

I'm glad to hear that you replaced all the original components when you discovered the 'no sound' problem. Good diagnostic technique

A couple questions so that we're on the same page.
Before you did any modifications, it worked just fine - good sound, no excessive noise, static or rattle?
Besides swapping out tubes and speaker, did you do anything else to modify the amp before discovering the problem?
At this point, with the amp on, you can hear a hum, or slight buzz with the amp on, but no guitar signal?
The guitar and cord work in another amp (silly question, I know!)?

With the amp on and the volume all the way up to 12, can your hear any change in the sound the amp makes by turning the tone knob from one extreme to the other? If you plug a guitar cable into the input jack (try each one) is there any kind of crackle as the plug is inserted or removed?

[Michael070]

Hi Eschertron and thank you for responding. To start with your questions, I had only had the amp a couple of weeks and only got to plug into it a couple of times but yes, the amp worked fine, sounded good, nice and clean and there were no apparent signs this was about to happen. The tubes and speaker were the only thing I touched, up to that point, and would have probably been about the end of it but now there's obviously more that needs to be done. I can hear power and sometimes a hum in the speaker but it does not seem to adjust with the volume and although you'd think it's a silly question but it was about 24 hours before the light bulb went off and I rushed downstairs to plug into another amp and fortunately but unfortunately, The guitar and the cable are fine. Even with multiple guitars and multiple cables.. And not sure if this would factor but for informational purposes, I replaced the 6v6 with a Ruby and I replaced the 12ax7 with a vintage Sylvania 12ax7. Oh and no crackle from the input jacks with a cable inserted.

[Justin Thomas]

PCB-mounted everything. If you're new to tube amps, is there a chance a solder joint/trace on the board was broken/cracked? Rough handling can do that. I'm not blaming - it's just that fragility of things that should not suffer it is an unintended side effect of our disposable society. I remember having to be quite forceful in removing the tubes from my first tube amp... it's totally NOT your fault if you don't know any better!

Justin

[DrGonz78]

Have you tried putting the original tubes back in the unit to see if that makes it work again? Perhaps that old sylvania tube has a bad preamp stage and is not passing signal.

[Michael070]

Justin - I have considered that and it's still possible but one of the first things I did when I got the chassis out was look at the solder connections in and around the 12ax7 and I dont see anything that stands out to me but that doesn't mean it isn't there. I'll try to get some detailed pictures up today to see if you guys see anything I do not.
Dr. Gonz - Faster than you could say "OH s41t MY AMP ISN'T WORKING!" That was the first thing I did when I finished scratching my head and picked my jaw up off the floor.

[Michael070]

Not sure if these will help. I centered on and around the 12ax7. Not sure if the previous owner changed anything or not.

[eschertron]

Justin brings up a good point, if the only thing that was done to the amp was pulling/pushing tubes, then could be mechanical stress on the PCB. Also the wires to the speaker? I don't recall if they go to push-on connectors, but if they don't, perhaps a stress fracture there?

I like the fact that 4 screws and the chassis slips out. Be sure to take caution about high voltage with the chassis out, read up on power supply cap discharge before poking around on the board. Speaking of poking, an honest-to-goodness bamboo chopstick is good for testing wires and flexing the board; checking for cracked solder or intermittent opens. If you decide to power up outside of the cabinet, be extra careful. There's no good way to support the chassis in a workable position without building a service jig out of some available wooden boards (for example, but clearly something non-conductive). Stability is key to avoiding damage to the amp and yourself.

The next troubleshooting excercise is arguably to measure voltages on the amp. If you don't have the test equipment and are not familiar with it's use, find a buddy with some experience around high volts. No kidding.
http://support.fender.com/schematics..._schematic.pdf
The test points with the voltages labeled DC would be the first to check off the list. Write down (preferably directly onto a printout of the schem) exactly what is measured. Later in the troubleshooting process you'll be thanking yourself.

Also you mentioned a volume pot. Is this something that you've added/changed on the amp at this point? If the amp is not totally stock, let us know so we can be advised.

edit:
I just saw your last post. Great shots! Good and clear

I'm curious about the funky blemishes around the edge of the board. Salt deposits? PCB substrate peeling away? Can you inspect and shed some light on that? It's probably nothing, but worth consideration.

[g1]

Seeing as you mentioned you are new to tube amps, you said the 12AX7 was lit, but are both halves of it lit?