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Post subject: Re: My Modded Champion 600
Posted: Thu Nov 03, 2011 6:22 pm
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stratele52 wrote:
My poor American reading


Compounded by my poor American writing. :lol:

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Post subject: Re: My Modded Champion 600
Posted: Fri Nov 04, 2011 4:50 pm
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Well, I am now proud to say that this little amp is dynamite: Loud, smooth distortion, very touch sensitve. Goes from clean to very dirty with a touch of the volume control or a dig with the pick. :D

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Post subject: Re: My Modded Champion 600
Posted: Fri Nov 04, 2011 5:37 pm
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Was there ever a doubt? :lol:

Good job bluesky636, we'll make a tech out of you yet. :lol:

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Post subject: Re: My Modded Champion 600
Posted: Fri Nov 04, 2011 5:48 pm
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shimmilou wrote:
Good job bluesky636, we'll make a tech out of you yet. :lol:


LMFAO

Bill could likely teach us all a thing or two.

:mrgreen:

Arjay

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Post subject: Re: My Modded Champion 600
Posted: Fri Nov 04, 2011 7:10 pm
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Retroverbial wrote:
shimmilou wrote:
Good job bluesky636, we'll make a tech out of you yet. :lol:


LMFAO

Bill could likely teach us all a thing or two.

:mrgreen:

Arjay


I've learned more about tube guitar amps from you guys than I did in college 35 years ago. :D

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Post subject: Re: My Modded Champion 600
Posted: Thu Nov 17, 2011 11:06 pm
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I made one last mod to the little beastie tonight.

I removed the cathode bypass cap (C3) on the first half of the preamp tube (I had already removed the cap (C10) on the second half). As expected, the gain dropped by about 5 to 6 dB. To compensate, I replaced the 5751 with a JJ 12AX7 which brought the overall gain back up to just about where it was previously. The amp cleaned up just a little bit and the overdrive with the amp and guitar volume controls dimed was a little thicker with slightly more midrange and less "fizz" on the overdrive. I like it a lot, so it will stay this way. This mod brings the circuit more in line with the Champ 5F1 circuit:

http://ampwares.com/schematics/champ_5f1.pdf

I also experimented with replacing the power supply divider resistors (R11 and R12) with the same value resistors used in the 5F1 power supply. I first replaced the 10K R12 (C600 schematic in my first post) with a 22K, 2 watt resistor as used in the 5F1 circuit. This dropped the plate voltage to the 12AX7 with the result that the gain dropped enough to make it difficult to get any overdrive at max volume settings. The amp was just too clean, so I swapped back to the stock 10K ohm resistor. I decided not to try replacing R11 as the screen voltage in the C600 is already set by a 470 ohm screen resistor. I felt it didn't need to be dropped any more.

The bottom line now is that with the exception of the power supply and a couple of grid and screen resistors, the C600 circuit is virtually identical to the 5F1 circuit. The overdrive is great. Bass response is much improved over stock. The amp cleans up very nicely with the guitar volume control. I'm very happy with the amp in this final configuration.

Now what do I do? I'm bored. :lol: :lol: :lol:

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Post subject: Re: My Modded Champion 600
Posted: Thu Nov 17, 2011 11:33 pm
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bluesky636 wrote:
Now what do I do? I'm bored.


Build a 5E3 clone......?

:mrgreen:

Arjay

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Post subject: Re: My Modded Champion 600
Posted: Fri Nov 18, 2011 12:16 am
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This one looks cool, and decent price. Scroll down to "New Deluxe Head". I'm looking at 6V6 heads and ran across this.

http://www.stf-electronics.com/

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Post subject: Re: My Modded Champion 600
Posted: Fri Nov 18, 2011 7:51 pm
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I am seriously contemplating building something next year when more funds are available. In the meantime, I have ordered this book:

http://www.amazon.com/Circuit-Analysis- ... 047&sr=8-1

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Post subject: Re: My Modded Champion 600
Posted: Sat Nov 19, 2011 3:05 am
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Look to be a useful book


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Post subject: Re: My Modded Champion 600
Posted: Sat Nov 19, 2011 7:15 am
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stratele52 wrote:
Look to be a useful book


It should satisfy the engineer half of my brain. :lol:

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Post subject: Re: My Modded Champion 600
Posted: Sat Mar 03, 2012 8:16 pm
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Well, now that my Weber 5F6A is all dialed in I had some spare time tonight so I took a second look at my modded C600. I ended up taking it all the way to a PCB based 5F1 circuit.

To do so I removed the following resistors and replaced them with short jumpers: R14, R17, R25, and R26.

I also removed R11 and moved the 10K ohm resitor in R12 to that position. I then put a 22K ohm, 2 watt resistor into the R12 position.

http://support.fender.com/schematics/gu ... ematic.pdf

The net result circuit wise is this:

http://ampwares.com/schematics/champ_5f1.pdf

I did keep the solid state rectifier and stock power supply caps, though. The amp is just a little bit quieter now due to the reduced voltage to the tubes, but the overdrive is smoother with no fizz or other noise. It cleans up really well with a lighter pick attack or rolling back of the guitar volume. The amp is dead quiet too. I'll post some sound samples later.

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Post subject: Re: My Modded Champion 600
Posted: Sat Mar 31, 2012 11:00 pm
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I started playing my modded C600 through a Raven 1x12 cabinet that I bought used at Guitar Center recently. I swapped the 8 ohm Celestion G12P-80 for a 4-ohm Fender/Eminence speaker. The 12" speaker instantly made the little 5 watter sound much bigger. The only problem was that the low bass was rather muddy sounding with the 5F1 circuit, particularly with humbuckers. So I decided to do a little surgery to the amp to make it more compatible with the 12" cab.

I first replaced the two 0.022 mfd coupling caps that I installed after pulling out the tone stack, with two 0.0022 mfd coupling caps. The 0.022 mfd caps have a low frequency -3 dB point of 7 hz, way too low for any useful bass. The 0.0022 mfd caps have a -3 dB point of 70 hz, much more in keeping with the 82 hz low E string of a guitar.

When I plugged things back together, I found that the low bass did indeed sound cleaner and less muddy, particularly when pushing the little amp hard. However, it seemed that the overall gain dropped slightly. To compensate, I reinstalled C3, the 22 mfd cathode bypass cap for the first half of the 12AX7 (I left the second half unbypassed). I plugged in again and BINGO! The gain was back up and the amp sounds fantastic through the 12" cab. It is still a little mid-rangey sounding, but the overall tone is brighter and less woofy with humbuckers and it sounds very clear and clean with single coils/stacked humbuckers. It overdrives very nicely with no more muddy bass.

The amp is now a hybrid of 5E1 and 5F1 circuits. I highly recommend this mod to those playing through a 12" external cabinet.

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Post subject: Re: My Modded Champion 600
Posted: Thu Apr 12, 2012 5:08 pm
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After much testing and listening, I finally settled on keeping the 8-ohm 12" Celestian in the cab and going back to the 5F1 configuration with the smaller coupling caps (no cathode bypass cap on the first half of the 12AX7). The Eminence speaker sounded good with single coils but was way too muddy with humbuckers. The Celestian works best with all. It also seems louder than the Eminence.

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Last edited by bluesky636 on Fri Apr 13, 2012 2:10 pm, edited 1 time in total.

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Post subject: Re: My Modded Champion 600
Posted: Fri Apr 13, 2012 12:32 pm
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bluesky636 wrote:
After much testign an listening, I finally settled on keeping the 8-ohm 12" Celestian in the cab and going back to the 5F1 configuration with the smaller coupling caps (no cathode bypass cap on the first half of the 12AX7). The Eminence speaker sounded good with single coils but was way too muddy with humbuckers. The Celestian works best with all. It also seems louder than the Eminence.


I was going to ask you if an 8" speaker would fit in the cab but I like the external 12" method more.

Cheers,

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