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Old 02-08-2008, 02:16 PM   #1
the.spine.surfs
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Fender Champ 600 Mods?

Has anyone tried working on or modding a Fender Champ 600? disregarding speaker and tube swaps, has anyone tinkered with differnt valued resistors anywhere on it? I've read that the lifting/lowering the value of r19 increases output, at risk of the OT. Anything else? Thanks.
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Old 02-08-2008, 05:10 PM   #2
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It's a Champ. Look for Champ mods.

You could add more filtering, add a tonestack, change the biasing of the tubes etc.
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Old 02-08-2008, 11:18 PM   #3
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Quote:
Originally Posted by mr_hankey
It's a Champ. Look for Champ mods.

You could add more filtering, add a tonestack, change the biasing of the tubes etc.

Looked! Searched through a few pages of google. I was hoping to meet someone who had opened one themselves.

It's auto biasing anyway. Poo.
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Old 02-08-2008, 11:34 PM   #4
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Change the 4.8K resistor in the tonestack circut for a 15K - 25K pot for a mid knob.
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Old 02-09-2008, 02:56 AM   #5
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Quote:
Originally Posted by mr_hankey
It's a Champ. Look for Champ mods.

You could add more filtering, add a tonestack, change the biasing of the tubes etc.
It's not exactly a Champ.

1 - It uses a smaller PT and a solidstate rectifier instead of a 5Y3 tube.

2 - It has an 8 ohm speaker and secondary on the OT, instead of a 4 ohm.

3 - The NFB resistor in the Champion 600 is 2.7k, not 2.2k 2.2k, not 2.7k.

4 - It has grid-stopper resistors (15k on the preamp sections, 1.5k on the 6V6) that don't exist on the Champ.

5 - It HAS a tonestack. But it has all fixed value resistors, instead of pots.
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Old 02-09-2008, 04:05 AM   #6
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SYK, could you tell me which resistors make up the tonestack, other than the one Kurt mentioned, so I could experiment with putting pots at those locations?

Thanks, Kurt.
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Old 02-09-2008, 05:30 AM   #7
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Picture, thousand words, blah, blah, blah ...

First pic is a schematic of the Champion 600 tone shaping
and components on the circuit board.
I don't have a pic of the foil pattern,
so I can't tell which ends of the resistors are connected to what.
Not a big deal, you should be able to figure that out.

The second drawing is a couple of Fender schematics with tonestacks.

To make things a bit easier for you, I put things in colour according to the following:

Treble
Bass
Middle



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Old 02-09-2008, 11:55 AM   #8
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SYK ftw.

A pretty good idea is just to run the Champion to a bigger cab.
Solves its boxiness.
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Old 02-09-2008, 12:29 PM   #9
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WHo they are using a 15K for mids....whatever you can still add pots to all of them. You might want to change C8 to 0.15mF for better clearer bass response. Also on vintage Fenders C1 was 270pF....change from 250pF to 270pF you will probbly not hear a thing but Im juts putting it out there.

SYK how would you add a NFB switch?
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Old 02-09-2008, 12:51 PM   #10
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Quote:
Originally Posted by forsaknazrael
SYK ftw.

A pretty good idea is just to run the Champion to a bigger cab.
Solves its boxiness.

Ah, definitely. I'd buy him a beer...if I were 21. Shame.

And I'm also thinking about getting a 2x12" cab built. I'll probably use it with the speaker in my Palomino V16 until the cab is built. Is there any chance of upgrading the speaker? I know a cab would be better, but it would be nice to be able get some nice tone out of it without dragging a cab around.

Thanks again, everyone. I'll be tearing it open as soon as I get back home.
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Old 02-09-2008, 12:53 PM   #11
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I think before you do anythng to the amp internally you should try this amp with a 212.
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Old 02-09-2008, 12:53 PM   #12
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It's a 6", right?
Tedweber.com sells an affordable 6" replacement. They seem to think their Signature 6 kicks ass in the Champion 600. I can't speak from experience, so you'll have to check out reviews.
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Old 02-09-2008, 02:53 PM   #13
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Quote:
Originally Posted by kurtlives91
I think before you do anythng to the amp internally you should try this amp with a 212.

Well, I can try it with a Marshall 1960, a Peavey 4x12", and the speakers in a couple 1x12" Fender and Palomino combos. I'll be sure to do that tommorow.

forsaknazrael, thanks for the info. I hadn't found any 6" speakers anywhere! I heard scuttlebut about some guys stuffing 8" speakers in it, but I really don't want to even pretend that I'm making this into anything but a small quiet practice/recording amp.
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Old 02-09-2008, 02:55 PM   #14
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Yeah, Weber reckons their Alnico Sig 6 is pretty good. Hence their (humorous) advert.
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Old 02-09-2008, 03:41 PM   #15
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Mesa Boogie mark something?

Sorry wrong amp, got mixed up with the princeton
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Old 02-09-2008, 03:57 PM   #16
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Quote:
Originally Posted by kurtlives91
SYK how would you add a NFB switch?
Either of two methods will work.

You can short the node that the red arrow points to,

OR you can put a switch between that node and the 2700 ohm resistor, to disconnect it.


Quote:
Originally Posted by the.spine.surfs
Well, I can try it with a Marshall 1960, a Peavey 4x12", and the speakers in a couple 1x12" Fender and Palomino combos. I'll be sure to do that tommorow.

forsaknazrael, thanks for the info. I hadn't found any 6" speakers anywhere! I heard scuttlebut about some guys stuffing 8" speakers in it, but I really don't want to even pretend that I'm making this into anything but a small quiet practice/recording amp.
It always gets a bit dicey when you try to increase the size of a speaker.
Sometimes you can shoehorn one in, other times you just need a bigger shoe.

That said, there's a big difference between the cone area of a 6 and an 8.
(about twice as much)
Other things being equal, that will get you a ton more low end.
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Old 02-09-2008, 09:56 PM   #17
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Quote:
Originally Posted by SomeoneYouKnew
3 - The NFB resistor is 2.7k, not 2.2k

5 - It HAS a tonestack. But it has all fixed value resistors, instead of pots.


Well, I didn't know about that.

I suggest disconnecting the NFB loop, and bypassing the tonestack with a small cap, like .02uF. It'll get you much closer to the tweed Champ sound, and will give you more gain.
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Old 02-09-2008, 11:53 PM   #18
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What's this node?
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Old 02-10-2008, 09:03 AM   #19
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Here's another one (one I would definitely do): rip the pcb out, and rewire everything on an eyelet/turretboard. It's a very simple amp and you can just go by old Champ layout, so it shouldn't be very hard. It'll improve the reliability quite a bit, and further mods will be much easier.
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Old 02-10-2008, 10:10 AM   #20
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Quote:
Originally Posted by mr_hankey
Here's another one (one I would definitely do): rip the pcb out, and rewire everything on an eyelet/turretboard. It's a very simple amp and you can just go by old Champ layout, so it shouldn't be very hard. It'll improve the reliability quite a bit, and further mods will be much easier.

That's quite tempting. Could I still use some of the original components (tube sockets, transformer, etc.), or would they need to go?
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