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 Post subject: My Modded Champion 600
PostPosted: Sun Oct 30, 2011 1:37 pm 
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A few weeks ago I posted about the new Champion 600 amp that I had picked up and the mods plans I had for it:

viewtopic.php?f=13&t=62533

Well, all of the mods are complete and the little bugger sounds fantastic. I'll try to summarize the mods here (with photos and schematics), so if you bore easily you should leave now as this will be a bit lengthy. :lol:

The Champion 600 schematic is basically the same as the Silverface Champ amp, except the tone stack in the Champ 600 is fixed.

Champion 600 schematic:

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

Silverface Champ schematic (AA764):

http://ampwares.com/schematics/champ_aa764.pdf

I did a fair amount of research on the Web and found a lot of interesting mods for the Champion 600. In the end, I basically converted my amp to the schematic of 1956 Tweed Champ.

1956 Tweed Champ schematic (5E1):

http://ampwares.com/schematics/champ_5e1.pdf

The basic Champion 600 is a pretty well built little amp, with a decent tone right out of the box. But there is room for improvement. On the plus side, the cabinet and chassis/PCB are well built. It just exudes "cool" in its looks. On the negative side, the amp is stuck with cheap Chinese tubes, a cheap Chinese speaker, and a thick, opaque grille cloth that muffles whatever sound the speaker is able to generate. To refresh everyone's memory, here is the stock Champion 600:

Image

The first thing I did was rip out the stock grille cloth and speaker. The grille cloth was replaced with a dark brown, acoustically transparent cloth:

Image

The stock speaker was replaced with a 6" Jensen Mod speaker:

Image

That was the easy stuff. On to the harder stuff (the electronics). I should note that it was not necessary to remove the main PCB from the chassis to do any of the circuit mods. The component mounting holes are plated through, so it was easy to unsolder/solder components from the top side of the board. The input PCB did have to be removed to replace the volume pot and add the revoicing capacitor to the low level input, though.

The first mod to the main PCB was the removal of all components that make up the tone stack (C1, C8, C9, and R18, R19, R20, R21, R22). Once those components were removed the two halves of V2 were coupled with a 0.022mF DC blocking capacitor. (I used a Mallory 150M type cap. I also used the same type cap to replace the cheap coupling cap used in C2).

Next, I removed the cathode bypass cap (C10) from the second half of the preamp tube. I also removed R3 and R23 from that circuit. A jumper wire was installed where R3 was, and a 1.5K 1/2 watt resistor was installed where R23 was. This simplifies the cathode circuit and brings the feedback resistor into the proper point in the circuit. The feedback resistor (R7) was replaced with a 22K ohm 1/2 watt resistor. Here is a photo of the modded main PCB:

Image

Then I moved on to the input PCB. The input PCB was removed and a Dremel tool was used to slice off the portion of the board that held the cheap plastic volume control. A 0.022 mF Orange Drop cap was soldered across R5. This rolls off the bass a bit on the low level input and keeps humbuckers from sounding too muddy through the amp. To mount the cap I just bent up the legs of the cap and slipped them under the leads of R5. I then squeezed them shut and soldered the cap to R5. Here is a photo of the modded board:

Image

Nothing was done to the chassis:

Image

Finally, the chassis was installed in the cabinet for a trial run:

Image

After the initial checkout, I experimented with preamp tubes. For the power tube, I used a JJ 6V6S. I had a choice of tubes for the preamp:

1. NOS JAN GE 12AY7
2. NOS JAN Philips 5751
3. JJ 12AX7
4. JJ high-gain 12AX7

One thing to note is that the removal of the tone stack results in a significant increase in gain through the amp, so it is a lot easier to send the tubes into overdrive. To steal a line from "Goldilocks and the Three Bears", I found the two JJ 12AX7s to be too hot (the amp broke up way to early which made it hard to get a clean tone), the 12AY7 was too cold (the amp stayed clean with the amp volume dimed and the guitar volume almost so), but the 5751 was "just right". I was able to dime the amp, turn the guitar down and get a nice loud clean tone, or turn the guitar up all the way up for some sweet overdrive.

Before buttoning everything up, I measured the bias setting of the 6V6S. Using my bias probe and DVM I measured the cathode current at 43 mA and plate voltage at 324VDC. Using the Weber bias calculator, the plate current was approximated at 41 mA. Taking into consideration the tolerance of all the measurements, the % of max plate dissipation for the JJ 6V6S is about 93% - 95%. A bit hot, but there is no sign of redplating and the tube sounds really good. I'll probably spend some time looking into ways to reduce the bias levels down to around 90%.

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Last edited by bluesky636 on Sat Nov 03, 2012 4:32 pm, edited 1 time in total.

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 Post subject: Re: My Modded Champion 600
PostPosted: Sun Oct 30, 2011 1:48 pm 
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So, how does the amp sound now? Terriffic! The gain is significantly increased by removal of the tone stack. Changing the feedback circuit cleans the sound up a bit while keeping a nice "edge" to things. Bass response is greatly improved and farting eliminated. The amp actually sounds quieter than stock. Hiss is almost non-existant and hum is also reduced (you have to put your ear up to the amp to hear any hiss or hum). I can easily overdrive the the amp with any guitar I own (I run an Electro-Harmonix LPB-1 set at 9:00 in front of the amp if I really want to crank things), yet it cleans up nicely while staying at a decent loudness just by rolling back on the guitar volume. All in all I am very pleased with the results. The mods were fairly easy and took about 6 hours to complete.

Oh, I don't have any recording capabilities, so I can't let you hear what the amp sounds like (I have a hand held digital recorder on my Xmas wish list 8) ). Besides, you really don't want to hear what I sound like, so you'll just have to take my word. :lol:

Hope you all enjoyed my little saga. :D

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 Post subject: Re: My Modded Champion 600
PostPosted: Sun Oct 30, 2011 4:15 pm 
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Damn fine job, Bill!

Significant sonic, cosmetic, and reliability improvements all around -- what did the total for these upgrades run?

RAWK ON!

8) 8) 8)

Arjay

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 Post subject: Re: My Modded Champion 600
PostPosted: Sun Oct 30, 2011 6:15 pm 
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Retroverbial wrote:
Damn fine job, Bill!

Significant sonic, cosmetic, and reliability improvements all around -- what did the total for these upgrades run?

RAWK ON!

8) 8) 8)

Arjay


Thanks, Arjay.

Speaker, caps, volume pot, chicken head knob to fit the pot was about $32 with shipping. The grille cloth was about $15 but half of that was shipping. Most of the tubes I had all ready but the 6V6S was $15 plus shipping. I figure I spent less than $75 with a few additional odds and ends. The amp cost me about $140 on sale.

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 Post subject: Re: My Modded Champion 600
PostPosted: Sun Oct 30, 2011 6:45 pm 
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Not bad......not bad at all!

8)

Arjay

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 Post subject: Re: My Modded Champion 600
PostPosted: Sun Oct 30, 2011 9:49 pm 
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Found one minor problem tonight. The amp is now loud enough that certain notes cause the elements of the 6V6S to rattle. I know that's what it is as I was able to hit those notes and touch the tube with my finger tip. You can really feel the tube shake. I have ordered one of the large tube damper rings from Eurotubes as well as an extra 6V6S (just in case). Hopefully that will solve the problem. I also noticed that with the back on the cabinet a lot of air pressure builds up which may be aggravating the tube vibration. I'll try playing without the back and see if that helps. If it does, I may cut the back up so that there is a larger opening which should allow for better air flow. That little 6" Jensen can really move a lot of air. :lol:

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 Post subject: Re: My Modded Champion 600
PostPosted: Sun Oct 30, 2011 10:47 pm 
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A couple of one-inch holes directly to the rear of the speaker should solve that, Bill.

HTH

Arjay

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 Post subject: Re: My Modded Champion 600
PostPosted: Mon Oct 31, 2011 2:01 am 
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Great job.


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 Post subject: Re: My Modded Champion 600
PostPosted: Mon Oct 31, 2011 10:17 am 
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Solders are in metallic "via" from PCB top to bottom, that good for reliability ! :lol:

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 Post subject: Re: My Modded Champion 600
PostPosted: Mon Oct 31, 2011 12:10 pm 
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Very cool bluesky636

I like what you did with the input board, the jacks are pretty good actually, and no stress on the solder joints since the board isn't mounted to the chassis.

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 Post subject: Re: My Modded Champion 600
PostPosted: Mon Oct 31, 2011 6:58 pm 
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Retroverbial wrote:
A couple of one-inch holes directly to the rear of the speaker should solve that, Bill.

HTH

Arjay


Well, the amp comes standard with a 2 3/4" x 4 3/4" hole directly behind the speaker already. :lol:

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 Post subject: Re: My Modded Champion 600
PostPosted: Mon Oct 31, 2011 6:58 pm 
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stratele52 wrote:
Great job.


Thanks. :D

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 Post subject: Re: My Modded Champion 600
PostPosted: Mon Oct 31, 2011 6:59 pm 
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Tis-san wrote:
Solders are in metallic "via" from PCB top to bottom, that good for reliability ! :lol:


Not sure I understand your comment. :?: :?: :?:

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 Post subject: Re: My Modded Champion 600
PostPosted: Mon Oct 31, 2011 7:01 pm 
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shimmilou wrote:
Very cool bluesky636

I like what you did with the input board, the jacks are pretty good actually, and no stress on the solder joints since the board isn't mounted to the chassis.


Yeah, I decided it would be more trouble than it was worth to replace the jacks with metal ones.

I ordered a vibration damping ring and 6V6S tube (just in case) from Eurotubes this morning. Hopefully that will eliminate the need to cut up the back panel.

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 Post subject: Re: My Modded Champion 600
PostPosted: Mon Oct 31, 2011 7:41 pm 
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bluesky636 wrote:
Tis-san wrote:
Solders are in metallic "via" from PCB top to bottom, that good for reliability ! :lol:


Not sure I understand your comment. :?: :?: :?:


Maybe referring to "through-hole" plating on the construction of the solder connections. Very solid. :idea:

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