Wow, it's been a while since I posted anything on here. I did get the parts for my mods. I changed my approach a little but I must say I'm satisfied with the results.
I'll start with the first preamp stage. I had taken out the cathode bypass capacitor as per a recommendation but I noticed a loss in gain. I discovered why when I studied tube amp design. The capacitor has no effect on the DC circuit so the cathode bias primarily controlled by the cathode resistor is unchanged. But for the guitar signal's AC the capacitor makes it act like the cathode is connected directly to ground so that the gain will not be limited by the cathode resistor. I took the direction that I had been recommended in one of the websites I visited and changed the plate resistor, cathode resistor and placed a new cathode bypass capacitor in the first preamp circuit. The plate resistor (R8) was 100k ohms 1/2 watt. I replaced it with a 1 watt 220k resistor. The cathode resistor (R2) was 1.5k 1/4 watt. I replaced it with a 1/2 watt 3k resistor. By the way, I did not check my bias current which could be bad. I had to stray a little bit for the recommended resistor values. This could effect the life of the tube. The original bypass capacitor was a 22uF/25V electrolytic. I read that such a high capacitance provides a flat gain throughout the guitar's entire frequency range. The replacement is a .68uF/630V Solen "Fast" Cap. The lower capacitance provides a bass rolloff that was recommended. The entire circuit change was to change the shape of the guitar signal away from the stock Fender shape. If that is an issue don't do it. But don't cut out C3 unless you want lower gain out of the first preamp stage.
The tone stack after the first preamp was the big gain killer. I had been recommended bypassing the entire circuit with a 0.22uF capacitor so I bought a switch to choose either circuit. I opted instead to keep the tone stack in place and just boost the gain by doubling the value of the midrange resistor (R19). I replaced a 15k 1/4 watt resistor with a 31k 1/2 watt resistor. Also, I replaced the treble capacitor (250pF) with a silver mica capacitor of the same value. I was recommended certain types of capacitors for improving tone. I also read though that Fenders used ceramic caps in their tone stacks. I can't recall if the original was ceramic but since I already took out the Fender "tone" it didn't matter. Since I was no longer bypassing the tone stack I took my new orange drop 0.22uF capacitor and replaced the second preamp output capacitor with it for improved tone. By doubling the resistance of R19 I got a noticeable gain boost and I like how the distortion sounds at the higher volume. Success.
This will conclude my guitar amp project for a while. I'm still up in the air about the speaker. Lots of people swear by replacing it. I don't know if I want to deal with a 6 inch speaker or just plug a 12 inch speaker in a cabinet into the speaker jack in the amp. Anyway I'm happy for now.
Note: Sharing this information was not to tell you step by step what to do to make better sounds out of a Fender Champion 600 amp. It is only telling you what I did. The risks taken by me to make these these mods are my responsibility. Doing any mods to your own amp is your responsibility. If your amp is under warranty it will not be afterwards. I was an electronics technician for seventeen years. Tube amplifiers use higher voltages than what comes out of your wall. Capacitors charge up and discharging a cap with your body can be dangerous. A proper soldering iron and some soldering experience is necessary to keep from damaging the printed circuit board. Don't look at what I did to be any better than the others who modified their amps. And so on...
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