champ amp tubes/speaker???

rexious · April 9th, 2008, 03:12 AM

someone told me that you could replace the tubes in a silverface champ amp without biasing them or anything, just pop them on in. is this true??? also i was thinking about replacing the original speaker of my champ with a better sounding speaker if anyone has any suggestions it would be appreciated.

kp8 · April 9th, 2008, 03:53 AM

I have one of them Italian jensens in mine. Not the Mod series but the Special Design ones.... great sounding speaker! It is still a 8" speaker and the small enclosure doesn't help, but that is about as good as an 8" speaker is gonna sound iffin you axe me.

Sidney Vicious · April 9th, 2008, 06:38 AM

Quote:

Originally Posted by rexious

someone told me that you could replace the tubes in a silverface champ amp without biasing them or anything, just pop them on in. is this true??? also i was thinking about replacing the original speaker of my champ with a better sounding speaker if anyone has any suggestions it would be appreciated.

Yes.

Weber Sigs are good - and cheap.

eugenedunn · April 9th, 2008, 11:23 AM

Depends on what kind of an amp tone you're chasing.

I have a 79 Champ that has been optimized for more clean headroom, but still have overdrive and punch when dimed and guitar volume dimed.

I asked Ted Weber what speaker would maximize clean headroom in the 8-inch 3.2 ohm format..... he recommended the 8F125. It is super beefy compared to the stock speaker. Takes a bit of wailing away to break-in, but it is so sweet now. Check my member gallery for pictures of the install. The speaker fits perfectly.

I have tried many different tubes in my Champ. Depending where you want to go, you have many preamp tube choices. 12AX7, 5751, 12AT7, and my favorite lower gain tube in V1 is the 12AY7. Anything lower, I have found to be too anemic sounding, and you lose punch.

Geno

bradpdx · April 9th, 2008, 04:16 PM

I use a Weber Sig8S in a BF Champ that works really well. Cheap, too - about $40 as I recall.

The biasing question has come up recently on TDPRI. Champs technically do not require biasing - the simple feedback circuit will adjust itself to most typical 6V6s you put in there. However, many BF/SF Champs do run the 6V6 right at the edge of self-destruction, with unacceptably high power dissipation.

This isn't really due to the bias scheme per se - I have tested dozens of 6V6s on Champs and found that they all "self bias" to within a very close margin of one another. The problem is the high plate voltages that result in excessive power in the tube with the simple biasing scheme.

BF/SF Champs are supposed to run the 6V6 at a plate-cathode drop of about 330VDC and a plate current of about 40mA. That produces a power dissipation of 330 x 0.040 = 13.3 watts, which is very close to the rated maximum of 14 watts. That is fine for a single-ended class A amp.

In fact, many BF/SF Champs run the plates much higher. My '66 BF Champ was running at about 410VDC B+ when stock, which translated into a power dissipation of 17.4 watts (!!) - quite a bit too high. The result was reduced tube life and a harsh, constricted sound.

I cannot be certain about this, but I have a hunch that this is one of the key reasons why the old tweed Champs are preferred to BF/SF ones - yes, the tone circuit is radically different, but tweeds just don't run the 6V6 at these insane levels. I should do some more research into that.

The best solution is to reduce the plate voltage back into the neighborhood of 350VDC. This requires a modification of the power supply, using either zener diodes or dropping resistors. My old '66 Champ now runs the plate at around 350VDC and the difference in sound is striking - open and dynamic with much smoother and more useful overdrive. I have tested it with many 6V6s and now the self-biasing scheme works as intended - all of them land in a perfectly acceptable spot and sound great.

rexious · April 10th, 2008, 03:58 AM

bradpdx thanks for the great info, could you possibly explain how to do the modification(the best and easiest of the two). im not much of an electrical wizz just a dumbie that can use a soldering iron and follow directions. hope this isnt a ridiculous question to ask of someone but if it is just overlook it. thanks for your help..

Scott S · April 10th, 2008, 04:06 AM

For what it's worth, the max rated dissipation for a 6V6 is actually 12W. The 14W 6V6GTAs and JJs were a later development.

BTW, I'm nursing a friend's '66 Champ back to health -- I should check its idle dissipation, just for kicks.

- Scott

April 9th, 2008, 03:12 AM	#1 (permalink)
rexious TDPRI Member Join Date: Mar 2008 Location: new orleans Age: 21 Posts: 17	champ amp tubes/speaker??? someone told me that you could replace the tubes in a silverface champ amp without biasing them or anything, just pop them on in. is this true??? also i was thinking about replacing the original speaker of my champ with a better sounding speaker if anyone has any suggestions it would be appreciated.

April 9th, 2008, 11:23 AM	#4 (permalink)
eugenedunn Tele-Holic Join Date: Dec 2006 Location: Sacramento, CA Age: 55 Posts: 803 37 Photos	Depends on what kind of an amp tone you're chasing. I have a 79 Champ that has been optimized for more clean headroom, but still have overdrive and punch when dimed and guitar volume dimed. I asked Ted Weber what speaker would maximize clean headroom in the 8-inch 3.2 ohm format..... he recommended the 8F125. It is super beefy compared to the stock speaker. Takes a bit of wailing away to break-in, but it is so sweet now. Check my member gallery for pictures of the install. The speaker fits perfectly. I have tried many different tubes in my Champ. Depending where you want to go, you have many preamp tube choices. 12AX7, 5751, 12AT7, and my favorite lower gain tube in V1 is the 12AY7. Anything lower, I have found to be too anemic sounding, and you lose punch. Geno __________________ Ono Boy says "good n' swampy....."

April 9th, 2008, 04:16 PM	#5 (permalink)
bradpdx Tele-Holic Join Date: Jul 2006 Location: Portland, OR Age: 50 Posts: 872 1 Photos	I use a Weber Sig8S in a BF Champ that works really well. Cheap, too - about $40 as I recall. The biasing question has come up recently on TDPRI. Champs technically do not require biasing - the simple feedback circuit will adjust itself to most typical 6V6s you put in there. However, many BF/SF Champs do run the 6V6 right at the edge of self-destruction, with unacceptably high power dissipation. This isn't really due to the bias scheme per se - I have tested dozens of 6V6s on Champs and found that they all "self bias" to within a very close margin of one another. The problem is the high plate voltages that result in excessive power in the tube with the simple biasing scheme. BF/SF Champs are supposed to run the 6V6 at a plate-cathode drop of about 330VDC and a plate current of about 40mA. That produces a power dissipation of 330 x 0.040 = 13.3 watts, which is very close to the rated maximum of 14 watts. That is fine for a single-ended class A amp. In fact, many BF/SF Champs run the plates much higher. My '66 BF Champ was running at about 410VDC B+ when stock, which translated into a power dissipation of 17.4 watts (!!) - quite a bit too high. The result was reduced tube life and a harsh, constricted sound. I cannot be certain about this, but I have a hunch that this is one of the key reasons why the old tweed Champs are preferred to BF/SF ones - yes, the tone circuit is radically different, but tweeds just don't run the 6V6 at these insane levels. I should do some more research into that. The best solution is to reduce the plate voltage back into the neighborhood of 350VDC. This requires a modification of the power supply, using either zener diodes or dropping resistors. My old '66 Champ now runs the plate at around 350VDC and the difference in sound is striking - open and dynamic with much smoother and more useful overdrive. I have tested it with many 6V6s and now the self-biasing scheme works as intended - all of them land in a perfectly acceptable spot and sound great. __________________ ---------- Tech Geek and Sensitive Artiste String bender ordinare!

April 9th, 2008, 03:53 AM	#2 (permalink)
kp8 Friend of Leo's Join Date: Aug 2004 Location: Charlottesville, VA Posts: 2,801	I have one of them Italian jensens in mine. Not the Mod series but the Special Design ones.... great sounding speaker! It is still a 8" speaker and the small enclosure doesn't help, but that is about as good as an 8" speaker is gonna sound iffin you axe me.

April 10th, 2008, 03:58 AM	#6 (permalink)
rexious TDPRI Member Join Date: Mar 2008 Location: new orleans Age: 21 Posts: 17	bradpdx thanks for the great info, could you possibly explain how to do the modification(the best and easiest of the two). im not much of an electrical wizz just a dumbie that can use a soldering iron and follow directions. hope this isnt a ridiculous question to ask of someone but if it is just overlook it. thanks for your help..

April 10th, 2008, 04:06 AM	#7 (permalink)
Scott S Tele-Afflicted Join Date: Dec 2005 Location: SW CR IA US NA PE Age: 28 Posts: 1,721	For what it's worth, the max rated dissipation for a 6V6 is actually 12W. The 14W 6V6GTAs and JJs were a later development. BTW, I'm nursing a friend's '66 Champ back to health -- I should check its idle dissipation, just for kicks. - Scott