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Post subject: Re: My Modded Champion 600
Posted: Fri Apr 13, 2012 2:11 pm
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mhowell wrote:
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.

Definitely preferable. :D

Cheers,


5/10/12: I failed to write a response and have now forgotten what it was I was going to say. :oops: :lol:

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Post subject: Re: My Modded Champion 600
Posted: Wed May 23, 2012 7:13 pm
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bluesky636 wrote:
The input PCB did have to be removed to replace the volume pot

Didn't find any details on the volume pot mod. Anything special about that mod or impedance you selected?

Comtemplating putting a 250k 'Treble' pot to replace R21 and R20 in the Tone Stack. The Tone Stack will be switchable from bypassed to a 'modified' Tone Stack curcuit. I will be following your Cathode Bias mod specs, if that helps. So curious if you have any thoughts or comments about a Treble control.

I did find this regarding the bias and R10;
Quote:
We have found that the installation of a 200 Ohm to 240 Ohm 2W resistor in series with the factory installed 470 Ohm resister in R10 will achieve approximately 12W to 13W power dissipation.

Is this relevent to your concern about the bias level?


regards,
Robert


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Post subject: Re: My Modded Champion 600
Posted: Wed May 23, 2012 9:40 pm
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sanctuary wrote:
bluesky636 wrote:
The input PCB did have to be removed to replace the volume pot

Didn't find any details on the volume pot mod. Anything special about that mod or impedance you selected?

Comtemplating putting a 250k 'Treble' pot to replace R21 and R20 in the Tone Stack. The Tone Stack will be switchable from bypassed to a 'modified' Tone Stack curcuit. I will be following your Cathode Bias mod specs, if that helps. So curious if you have any thoughts or comments about a Treble control.

I did find this regarding the bias and R10;
Quote:
We have found that the installation of a 200 Ohm to 240 Ohm 2W resistor in series with the factory installed 470 Ohm resister in R10 will achieve approximately 12W to 13W power dissipation.

Is this relevent to your concern about the bias level?


regards,
Robert


The cheap plastic volume pot was just replaced with a 1M Ohm, audio taper Alpha pot and the wiring modified as shown in the photo.

You could add a treble control if you like, although I'm not sure of the value of doing so. The amp is plenty bright with single coils while keeping a nice midrange bite. Adding the 0.022 mfd cap across the low input 68K ohm resistor creates a "bright" channel for additional treble with humbuckers. I decreased the cap to 0.015 mfd when I switched to the 12" cab and I am going to try a 0.01 mfd cap with slightly larger coupling caps to tune things for a better bass/treble compromise when switching between the 6" speaker and the 12" cab.

After making the power supply mods I rechecked the bias and found it to be at 86% max plate dissipation which is darn near perfect (class A amps are usually biased at about 90% max plate dissipation) so no other changes were necessary.

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Post subject: Re: My Modded Champion 600
Posted: Thu May 24, 2012 6:43 am
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bluesky636 wrote:
sanctuary wrote:
bluesky636 wrote:
The input PCB did have to be removed to replace the volume pot

Didn't find any details on the volume pot mod. Anything special about that mod or impedance you selected?

Comtemplating putting a 250k 'Treble' pot to replace R21 and R20 in the Tone Stack. The Tone Stack will be switchable from bypassed to a 'modified' Tone Stack curcuit. I will be following your Cathode Bias mod specs, if that helps. So curious if you have any thoughts or comments about a Treble control.

I did find this regarding the bias and R10;
Quote:
We have found that the installation of a 200 Ohm to 240 Ohm 2W resistor in series with the factory installed 470 Ohm resister in R10 will achieve approximately 12W to 13W power dissipation.

Is this relevent to your concern about the bias level?


regards,
Robert


The cheap plastic volume pot was just replaced with a 1M Ohm, audio taper Alpha pot and the wiring modified as shown in the photo.

You could add a treble control if you like, although I'm not sure of the value of doing so. The amp is plenty bright with single coils while keeping a nice midrange bite. Adding the 0.022 mfd cap across the low input 68K ohm resistor creates a "bright" channel for additional treble with humbuckers. I decreased the cap to 0.015 mfd when I switched to the 12" cab and I am going to try a 0.01 mfd cap with slightly larger coupling caps to tune things for a better bass/treble compromise when switching between the 6" speaker and the 12" cab.

After making the power supply mods I rechecked the bias and found it to be at 86% max plate dissipation which is darn near perfect (class A amps are usually biased at about 90% max plate dissipation) so no other changes were necessary.


Get 1M audio taper pot, check!
No need to mod R10, check!
Hold off on the Treble control mod

I am doing the Input Voicing mod so that should help with humbuckers in the new 'bright' or Low input. You're finding too much bass through the 12" so that's why you're going with lower cap values across R5? Is this through both channels or are you concentrating on the 'bright' channel here. It would be nice to switch between a 6" & 12" speaker for single coils and humbuckers so keep us posted on your results.

More Q's to follow as I prepare the shopping list. Finding that I can do some crazy mods on this amp and that's including a Fender Style 15W Output Transformer with 5K & 8K Ohm Primary to 4/8/16 Ohm Secondary for around $60. That includes Orange Drops, Mallory and Silva-Mica type caps and even carbon comp resistors.

Currently this Champ has Tong-Sol tubes (6V6 & 12AX7), a Jensen Mod6 speaker and oxblood grill cloth.

thank you,
Robert


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Post subject: Re: My Modded Champion 600
Posted: Thu May 24, 2012 7:21 am
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Below are the mods and values that I have found during my research so looking for any comments or suggestions. Wasn't sure how one mod would affect another so listed them all in this post. The notes or comments are for my benefit as I was researching to better understand the components and their effect. I freely plagarized the notes so let me know if there are any inaccuracies.

Input Invoice Mod
• R5 Orange Drop .047uf (416P) 600v cap across R5
Higher values will give a bit more low end, smaller values cut more low end so they sound brighter. With the cap in place the "low" input gets a big volume boost for everything but the bass frequencies making it sound more like another channel rather than a lower volume input. The effect is more dramatic for the "low" input but does affect the “high’ input too.

• Volume Control Replace with 1M Ohm audio taper Alpha pot


Cathode Bias Mod
• C10** (22 25w) Remove **
• R3 (1.5k) Replace with jumper wire
• R23 (47) Replace with 1.5k .5w
• R7* (2.2k) Replace with 22k .5w ( for NFL Mod switch)
• R9 (100k .5w) Change to: (200k .5w Carbon Film)


Preamp Stage Gain Mod (Switchable)
1. R2 (1.5k) Change to: (2.7k .5w Carbon Composition)
2. R8 (100k .5w) Change to: (200k .5w Carbon Film)
3. C3 (22uf 25v) Change to: (Spraque Atom 2uf 50v) with SPST switch (Gain)

Steps 1, 2, and 3 raise the preamp stage gain and apply a Marshall-style voicing to the preamp.

Step 3, replacing the ubiquitous 22uF cathode cap (C3) on the front end, rolls off the bass frequencies and tightens up the amp response.

• C10** (22uf 25v) Remove or do Cathode Bypass Mod with SPST switch or change to: (Spraque Atom 2uf 50v) with SPST switch (Gain)

C3 is the 1st half of the preamp (12AX7)
C10 is the 2nd half (cathode bypass capacitor)

What about 2 SPST switches or a 4 position rotary knob to switch C3 & C10 On or Off?


Tone Stack Mod (Switchable)
Mallory 150M .1uf 630v (CP-M150-1-630v) This is a coupling cap for the tone stack.

• R19 (15k) Change to: (33k 1w Carbon Composition)

R19 is 15k resistor acting as a fixed midrange control. Doubling the value to 30k gives a nice gain boost and fattens the tone by increasing mids.

• C1 (250uf) Change to: (500uf 500v Silver-Mica)
At the top of the tone stack this cap controls treble pass. The treble ‘control’ is fixed at about ‘3’ via 2 resistors. This is fine. Any more treble and the tone would be too ‘frazzy. Replacing this cap shifts the treble corner frequency down an octave to also pass the upper-mids, yielding a nice, biting attack.

• C2 (.022uf 400v) Change to: Orange Drop .022uf (716P) 600v or Mallory 150M .1uf 630v (CP-M150-1-630v)

• C8 (.1uf 400v) Change to: Orange Drop .022uf (716P) 600v
• C9 (.47uf 400v) Change to: Orange Drop .022uf (716P) 600v or Orange Drop .047uf (418P) 600v

By installing .022uF caps at C8 & C9, you shift the response of the tone stack up as well, further cleaning up the low end and letting those mids punch out more.


Any help will be greatly appreciated!

regards,
Robert


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Post subject: Re: My Modded Champion 600
Posted: Thu May 24, 2012 8:17 am
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I took a look at everything you listed. I am not going to try and address each item one by one.

In my opinion, if you are considering doing ALL of these mods or some combination of them, you are making a mistake. The C600 is a very simple amp. Trying to turn it into an "everything" amp will result in an amp in which no single "voice" sounds its best. You will not make this into a Marshall or Vox or whatever sounding amp. Yes, you will alter the frequency response and gain of the amp but what it will end up sounding like is debatable. My suggestion would be to pick a type or year of amp to emulate and follow through on that.

The amp is already in the basic configuration of a Silverface Champ with a fixed tone stack. If you want to add functioning tone controls, great. The basic C600 configuration already has a fair amount of gain and a working tone stack would be useful. I chose to emulate a 5E1/5F1 Champ. In that configuration the amp sounds fantastic. The tweaks I am experimenting with now are primarily to make the amp compatible with either the internal 6" speaker or an external 12" speaker. These changes are only intended to make very minor changes to gain and frequency response, not to make the amp sound like a Marshall or somethign else it is not.

If you have a specific mod you would like advice on, I will be happy to help. However, I am not going to take the time to search through a barrel of apples looking for the one rotten one that will spoil the entire harvest.

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Post subject: Re: My Modded Champion 600
Posted: Thu May 24, 2012 8:36 am
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bluesky636 wrote:
I took a look at everything you listed. I am not going to try and address each item one by one.

In my opinion, if you are considering doing ALL of these mods or some combination of them, you are making a mistake. The C600 is a very simple amp. Trying to turn it into an "everything" amp will result in an amp in which no single "voice" sounds its best. You will not make this into a Marshall or Vox or whatever sounding amp. Yes, you will alter the frequency response and gain of the amp but what it will end up sounding like is debatable. My suggestion would be to pick a type or year of amp to emulate and follow through on that.

The amp is already in the basic configuration of a Silverface Champ with a fixed tone stack. If you want to add functioning tone controls, great. The basic C600 configuration already has a fair amount of gain and a working tone stack would be useful. I chose to emulate a 5E1/5F1 Champ. In that configuration the amp sounds fantastic. The tweaks I am experimenting with now are primarily to make the amp compatible with either the internal 6" speaker or an external 12" speaker. These changes are only intended to make very minor changes to gain and frequency response, not to make the amp sound like a Marshall or somethign else it is not.

If you have a specific mod you would like advice on, I will be happy to help. However, I am not going to take the time to search through a barrel of apples looking for the one rotten one that will spoil the entire harvest.


Thought I might be getting a little carried away with these mods. Found so many ideas out there! The intent was to have a complete set of mods planned and then work through them. Think I will take your lead and go with the 5E1/5F1 configuration. Good advice, this amp is what it is and shouldn't try to turn it into something else.

Will stick to specific questions moving forward.


thanks for your time,
Robert


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Post subject: Re: My Modded Champion 600
Posted: Thu May 24, 2012 10:52 am
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sanctuary wrote:
Thought I might be getting a little carried away with these mods. Found so many ideas out there! The intent was to have a complete set of mods planned and then work through them. Think I will take your lead and go with the 5E1/5F1 configuration. Good advice, this amp is what it is and shouldn't try to turn it into something else.

Will stick to specific questions moving forward.


thanks for your time,
Robert


Cool. 8)

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Post subject: Re: My Modded Champion 600
Posted: Thu May 24, 2012 10:57 am
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That is way too cool.

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Post subject: Re: My Modded Champion 600
Posted: Thu May 24, 2012 9:50 pm
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I made the final tweeks to my heavily modded C600 and it now works and sounds fantastic when using either the 6" Jensen Mod speaker or the cab with the 12" Celestion.

I finally settled on two 0.0033 mFd caps as the coupling caps (vice the 5F1 values of 0.022 mFd), and a bright cap on the low gain input of 0.01 mFd. The 0.0033 mFd coupling caps give a -3dB point for the low end of about 50 Hz vs the stock 0.022 mFd -3dB point of 7 Hz (What was Leo thinking? A 7 Hz low end with a 6"speaker? :shock: :lol: ). The bright cap of 0.01 mFd starts rolling the low end off at about 560 Hz making the 82 Hz 6th string down by about 12 - 15 dB from 1000 Hz.

The net result is a good solid bass with either a humbucker or single coil using either the 6"speaker or 12" speaker. When using the 6" speaker a humbucker or single coil guitar can be plugged into the high level input (the natural rolloff of the little speaker helps to clean up the bottom end which is now better controlled with a 50 Ha rolloff). When using the 12" cab, a humbucker plugs into the revoiced low gain input while a single coil plugs into the high gain input. Sounds great. I will try and make a few recordings of the various configurations this weekend.

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Post subject: Re: My Modded Champion 600
Posted: Sun May 27, 2012 5:25 am
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Would love to hear some clips Bill! :wink:

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Post subject: Re: My Modded Champion 600
Posted: Sun May 27, 2012 6:52 am
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Finally? I don't believe that you know the meaning of "final" do you? :lol: I'll be waiting for next week's revision. :lol: 8)

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Post subject: Re: My Modded Champion 600
Posted: Sun May 27, 2012 8:28 am
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tyronne wrote:
Would love to hear some clips Bill! :wink:


I hope to get a few posted this weekend. Word of warning, though, my amp skills are far better than my playing skills. :lol:

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Post subject: Re: My Modded Champion 600
Posted: Sun May 27, 2012 8:30 am
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shimmilou wrote:
Finally? I don't believe that you know the meaning of "final" do you? :lol: I'll be waiting for next week's revision. :lol: 8)


Well, you know what they say about us engineers: The enemy of the engineer is "I can make it better". :lol: :lol: :lol:

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Post subject: Re: My Modded Champion 600
Posted: Sun May 27, 2012 8:39 am
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I heard it as; "If it ain't broke.....you can prolly still fix it!" :shock:

Now, all that you need is a catchy name for your amp mod/building services and you're set.

Cool none-the-less. 8)

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