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Vintage threads from the first ten years

Silverface champ

11/14/1997 8:46 AM
Roger	Silverface champ How can I get my silverface champ to sound like a late tweed era champ. Roger

11/14/1997 9:19 AM
Whit	Hi Roger, Try comparing Champ schematics (some on this site, Pittman's book, elsewhere). See where the differences lie, and change that which you feel comfortable with. I love Champs myself, and a Silverface is a good place to tinker, since it wasn't altered extensively by CBS, and it has little "vintage" value (except to Champ afficiandos like myself). Speaker selection should not be overlooked either. I've just put 8 different types in my Champ project amp over the last week and each one has a different character. (It sounds great thru a 4-12 Marshall cab by the way) Ask yourself if you're aiming for an exact duplicate of a Tweed, or a sound which pleases you. I say this since my favorite mod to a Champ is to remove the feedback loop from OT to the 6V6 (usually via a switch). Not exactly "tweed" but it really stokes the fire! And define "sound like a late tweed era champ". (I ask retorically) There's tweed-when-new and tweed-after- a-few-decades-of-aging. But most of all, enjoy! There's a lot of great sounds to be had from the "little amp that can"... And stay tuned to this bulletin board, 'cause a few more knowledgable people than I may make my response look pitiful. ... Whit

11/14/1997 9:19 AM

Whit

Hi Roger,

Try comparing Champ schematics (some on
this site, Pittman's book, elsewhere).

See where the differences lie, and change
that which you feel comfortable with.

I love Champs myself, and a Silverface is
a good place to tinker, since it wasn't
altered extensively by CBS, and it has little
"vintage" value (except to Champ afficiandos
like myself).

Speaker selection should not be overlooked
either. I've just put 8 different types in
my Champ project amp over the last week
and each one has a different character.
(It sounds great thru a 4-12 Marshall cab
by the way)

Ask yourself if you're aiming for an
exact duplicate of a Tweed, or a sound
which pleases you. I say this since my
favorite mod to a Champ is to remove the
feedback loop from OT to the 6V6 (usually
via a switch). Not exactly "tweed" but it
really stokes the fire!

And define "sound like a late
tweed era champ". (I ask retorically)
There's tweed-when-new and tweed-after-
a-few-decades-of-aging.

But most of all, enjoy! There's a lot
of great sounds to be had from the "little
amp that can"...

And stay tuned to this bulletin board,
'cause a few more knowledgable people
than I may make my response look pitiful.

... Whit

11/14/1997 1:18 PM
Roger	The plate voltage is almost 100v higher in the silverface. Would it be a good idea to lower the plate voltages? I would like a champ that has some headroom ( not totally clipping but warm with good sustain ). Also the old champ has a 22k feedbk. res. , the newer has a 2700. Why the big difference in value? Roger.

11/15/1997 9:36 AM
Tony Taliaferro	These mod's are right out of Gerald Weber's book TUBE AMP TALK for the GUITARIST and TECH. I personally performed them on my silver face vibro champ and it now sounds awesome and very tweedy. I might not agree with some of his theory, like carbon composition resistors sounding better than metal film (golden ears?), but when it comes to quality of construction, materials and modifications he's pretty dam good. I hope I'm not breaking some sort of copyright laws or something but what the hell I bought both his books and its all in the name of TONE. Step 1; Get rid of the tone controls, they're designed to scoop mids and they reduce gain. Looking at the volume pot from the back, remove the wire from the right lead of the pot and tape it off. You can reverse these steps later if you don't like the sound or if you want it back to original spec's for selling or whatever. Now remove the wire from the right lead of the treble pot and solder it to the now empty right lead of the volume pot. Next, looking at board and coming off pin 1 of the first 12AX7 (there are two 12AX7's if you've got a vibro champ), you'll find a 250pf capacitor connected to two 100k ohm resistors. Change the 250pf capacitor to a 0.02uf cap rated for at least 400V if not more and remove the 100k ohm resistor that is mounted horizontally on the terminal board. It's the one that originally connected the 250pf cap to the 0.047uf and 0.10uf caps. Step 2; Change the feedback loop. From the speaker jack, there will be a wire running th the board connected to a 2700 ohm resistor. This is the feedback resistor. Change it to a 22k ohm resistor. One end still connects to the speaker connection eyelet but the other end now goes to pin 8 of the first preamp tube (12AX7). NOTE, there is already a wire on pin 8 so don't remove it. Step 3; Change one of the power resistors. On the far end of the terminal board near the multi-capacitor can terminals, there's a 10k 1-watt resistor. Change it to a 22k 1/2-watt resistor. That's it conversion to tweed complete! Enjoy! PS-If there's too much gain, remove (or even switch in and out for versatility) the electrolytic capacitor that's connected to pin 8 of the first preamp tube. It was put there to compensate for the loss due to the tone control circuit.

11/15/1997 9:36 AM

Tony Taliaferro

These mod's are right out of Gerald Weber's book TUBE AMP TALK for the GUITARIST and TECH. I personally performed them on my silver face vibro champ and it now sounds awesome and very tweedy. I might not agree with some of his theory, like carbon composition resistors sounding better than metal film (golden ears?), but when it comes to quality of construction, materials and modifications he's pretty dam good. I hope I'm not breaking some sort of copyright laws or something but what the hell I bought both his books and its all in the name of TONE.
Step 1; Get rid of the tone controls, they're designed to scoop mids and they reduce gain. Looking at the volume pot from the back, remove the wire from the right lead of the pot and tape it off. You can reverse these steps later if you don't like the sound or if you want it back to original spec's for selling or whatever. Now remove the wire from the right lead of the treble pot and solder it to the now empty right lead of the volume pot. Next, looking at board and coming off pin 1 of the first 12AX7 (there are two 12AX7's if you've got a vibro champ), you'll find a 250pf capacitor connected to two 100k ohm resistors. Change the 250pf capacitor to a 0.02uf cap rated for at least 400V if not more and remove the 100k ohm resistor that is mounted horizontally on the terminal board. It's the one that originally connected the 250pf cap to the 0.047uf and 0.10uf caps.
Step 2; Change the feedback loop. From the speaker jack, there will be a wire running th the board connected to a 2700 ohm resistor. This is the feedback resistor. Change it to a 22k ohm resistor. One end still connects to the speaker connection eyelet but the other end now goes to pin 8 of the first preamp tube (12AX7). NOTE, there is already a wire on pin 8 so don't remove it.
Step 3; Change one of the power resistors. On the far end of the terminal board near the multi-capacitor can terminals, there's a 10k 1-watt resistor. Change it to a 22k 1/2-watt resistor.
That's it conversion to tweed complete! Enjoy!
PS-If there's too much gain, remove (or even switch in and out for versatility) the electrolytic capacitor that's connected to pin 8 of the first preamp tube. It was put there to compensate for the loss due to the tone control circuit.

11/15/1997 10:36 AM
Roger	Thanks Tony, Does it say anything about lowering the B+? With lower plate voltages wouldn't it make the amp have a sweeter distortion ? Roger

11/15/1997 8:40 PM
Tony Taliaferro	That's why the 10k 1-watt resistor was changed to a 22k 1/2-watt resistor. Let me know how it turns out! Good Luck!

11/16/1997 6:02 AM
Roger	That 22K might take care of the preamp tube but I would think that 420v B+ should need to come down to about 350v(same as tweed). In the Q&A section of Gerald Weber's newer book he talks about lowering these voltages with a 56v zener diode connected between the plate winding center tap and ground in a Vibrolux. I wonder if this is safe to do in a Champ?

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