Champion 600 Mods

[dbharris]

Hi All,

I've been reading the site for about a decade, built several pedals over the years, and now decided the time was right to venture into the amp world. To start that journey, I wanted to mod my old practice amp a Fender Champion 600. My goal was really to just gain some experience, not expecting huge changes in tone. I wanted to keep the stock pcb and transformers (for now). I previously upgraded tubes, currently using a Mesa Boogie 12ax7 and Tung Sol 6v6GT or JJ 6v6S. Also changed the speaker for a Jensen Mod 6, and the grill cloth for Fender style oxblood. Those alone were big improvements.

Stock schematic https://www.google.com/url?sa=t&source= ... gMFGdvqhz6

For this set of mods I replaced all resistors (other than the metal oxide resistors) with 1/2 watt carbon film. But for the plates of the 12ax7 I used 1/2 watt metal film. Caps in the tone stack and coupling are 716p Orange Drops. Treble caps are silver mica (might swap for ceramics sometime). Cathode bypass caps are 10uf non-polarized electrolytics, I think they are Nichicon.

I wanted to do something a little different than the usual mods. So, I chose to insert a Brownface Pro 6g5 tone stack http://www.prowessamplifiers.com/schema ... matic.html. Hoping for something a little more rude than the Blackface tonestack that's stock, but keeping some clean headroom too. Treble and Bass pots were a must. The stock amp is nearly unusable with humbuckers due to the little speaker. I also reduced the size of the coupling cap before the tone stack and the cathode bypass caps to help cut some bass. Additional mods are a "character" switch to change the treble cap and slope resistor simultaneously between Fender and Marshall values (labeled USA / UK) and a global negative feedback switch (center off) to go from stock value to no negative feedback to less negative feedback (about 3x stock resistor value).

Here is the schematic for the mods:

IMAG1841.jpg

I had to do some trouble shooting for a wiring error but figured it out. Amp is working and behaves as it should. The treble and bass pots are great for dialing in a good sound from clean to mean and between guitars. The only issue I'm having is that my bass pot works like a cut. Do I just need to swap leads on lugs 1 and 3? I did that before and it did not change but that was prior to sorting out the wiring issue.

Voltages:
B+ 358.3

6v6 pins
1 about 5mv
2 3.275 vac
3 346.1
4 349.5
5 9.5 mv
6 about 1 mv
7 3.270 vac
8 21.95

12ax7 pins
1 211.9
2 0
3 1.692
4 3.278 vac
5 3.277 vac
6 211.7
7 0
8 1.745
9 3.273 vac

Before and progress pics:

IMAG1813.jpg

IMAG1815.jpg

IMAG1816.jpg

IMAG1817.jpg

More pics below

Thanks for reading!

-Dan

[dbharris]

IMAG1833.jpg

IMAG1834.jpg

IMAG1836.jpg

And finished product:

IMAG1835.jpg

IMAG1837.jpg

[bluesky1958]

I modded mine by ripping out the stock tone stack and replacing it with a Tweed 5F2A tone stack. I mounted the pot in place of the low level input jack. I also used a Weber 6" ALNICO speaker and a thin brown grille cloth. It's quite loud.

[Stevem]

For added tonal enhancement I would audition getting two Orange drop caps, a .22 and a .022 both at a 600 volt rating and wire them in parallel and then wire them across the first node of the power supply .

You can wire them to a DPDT mini switch and have them both in circuit, or just either one.

I would audition them first on as I stated the first node, and then on the last preamp node to see which provides the most benefit to your ear and importantly in low volume and cranked out.

Just note that a 630 volt .22uf cap is some 4 bucks!

[dbharris]

Hi bluesky, that sounds like a nice little amp with the Alnico. They are quite loud! For fun the other day I plugged mine into a 2x12 cab with WGS green berets and it can really move some air.

Stevem, do you mean to wire those caps in parallel with the first dropping resistor or before it between the B+ node and ground? I have some extra 716p orange drops kicking around. But not sure of the values. I still need to rewire the bass pot, so I may try this while I have her open anyways.

-Dan

[Stevem]

No, wire from the filter positive to ground/ across the filter.

[dbharris]

OK, thanks!

[bluesky1958]

Hi bluesky, that sounds like a nice little amp with the Alnico. They are quite loud! For fun the other day I plugged mine into a 2x12 cab with WGS green berets and it can really move some air.

-Dan

It almost seems louder and have more bass than the 5F1 Champ I built with an 8" ALNICO speaker and 5F2A tonestack! I plugged the 600 into an old cab I had with a 12" speaker (forgot the brand) and it rocked.