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Post subject: SF Champ - Weber speaker question
Posted: Fri May 21, 2010 8:36 pm
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I'm going to be ordering a replacement speaker for my SF Champ soon. I've read all the internet stuff and I'm going with the Weber 8A125. Now, the question I have is, does anyone know the real difference in tone between the 8A125 and the 8A125-O? The "O" description says it breaks up earlier - is that a good thing? I'm trying to get more gain out of my Champ so I'm thinking that's what I'd want, right?

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Posted: Fri May 21, 2010 9:44 pm
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You need a 4Ω speaker for that Champ, PTM.

The original actually was wound to 3.4 ohms but I don't think anybody makes those anymore.

If you use an 8Ω speaker in that amp you'll get substantially LESS volume, not more.

HTH

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Posted: Fri May 21, 2010 10:06 pm
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The "8" in 8A125 refers to the size, not ohms. They make them in 3.2 and 4 ohm.

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Posted: Fri May 21, 2010 10:39 pm
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Yeah, if you want earlier distotion, then the "O" is the way to go. It's my experience, that the Weber's take about 20hrs of variable playing to break in. Art

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Posted: Sat May 22, 2010 12:34 am
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Yes, 3.2Ω. Sorry, my bad.

I think Art's right about using the "O" Weber. You might also consider exchanging the amp's V1 12AX7 for a 12AT7 if earlier breakup is the goal.

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Arjay


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Posted: Sat May 22, 2010 9:00 am
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About the 3.2 ohms speaker.

I read in a book about Fender amps this speaker is a real 4 ohms, but somebody at ( fender ?) that time mesure it with ohmeter and read 3.2 ohms and write this mesure on Fender schematic.

I don't know if this story is true.

But to me it make sense because output transformer at this time are 8 ohms or 4 ohms.
We know 8 ohms speaker exist. So why, Jensen or others build a 3.2 ohms speakers ?


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Posted: Sat May 22, 2010 12:49 pm
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Retroverbial wrote:
Yes, 3.2Ω. Sorry, my bad.

I think Art's right about using the "O" Weber. You might also consider exchanging the amp's V1 12AX7 for a 12AT7 if earlier breakup is the goal.

HTH

Arjay


Well, my thought is that you aren't going to get great clean headroom out of a 5W amp, so I might as well get it to go a really good overdriven sound.

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Posted: Sat May 22, 2010 1:35 pm
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Champ are single ended amplifier ( one output tube) and this kind of amp, in my opinion, cannot have much headroom like a push pull output ( 2 tubes) amp.


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Posted: Sat May 22, 2010 1:42 pm
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/Users/louislafleur/Pictures/iPhoto Library/Originals/2010/10-05-16/DSCN2198.JPG


Sorry, I make a test


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Posted: Sat May 22, 2010 2:04 pm
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Powdered Toast Man wrote:
Retroverbial wrote:
Yes, 3.2Ω. Sorry, my bad.

I think Art's right about using the "O" Weber. You might also consider exchanging the amp's V1 12AX7 for a 12AT7 if earlier breakup is the goal.

HTH

Arjay


Well, my thought is that you aren't going to get great clean headroom out of a 5W amp, so I might as well get it to go a really good overdriven sound.


Twew dat, PTM. BTW I just tried the 12AT7 swap for V1 in my Bronco -- it did not seem to make much of a difference. It's possible you might have better luck with your Champ though.

I think the only method to really "supercharge" a Champ for loads of clean headroom would be to make major mods to the P/S and output stage. But it would of course "corrupt" a vintage amp -- for that much work it'd be better to start with a bare chassis kit and build something from scratch. Or take the next logical step and move up to a Princeton.

Arjay


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Posted: Sat May 22, 2010 2:22 pm
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Retroverbial wrote:
Powdered Toast Man wrote:
Retroverbial wrote:
Yes, 3.2Ω. Sorry, my bad.

I think Art's right about using the "O" Weber. You might also consider exchanging the amp's V1 12AX7 for a 12AT7 if earlier breakup is the goal.

HTH

Arjay


Well, my thought is that you aren't going to get great clean headroom out of a 5W amp, so I might as well get it to go a really good overdriven sound.


Twew dat, PTM. BTW I just tried the 12AT7 swap for V1 in my Bronco -- it did not seem to make much of a difference. It's possible you might have better luck with your Champ though.

I think the only method to really "supercharge" a Champ for loads of clean headroom would be to make major mods to the P/S and output stage. But it would of course "corrupt" a vintage amp -- for that much work it'd be better to start with a bare chassis kit and build something from scratch. Or take the next logical step and move up to a Princeton.

Arjay


I'm getting some JJ's and I'm ordering a hotter spec 12AX7 for the preamp. Should give me a bit more breakup.

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Posted: Sat May 22, 2010 4:44 pm
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12AY7 will make much difference the gain of this tube is 45
12AT7 gain is 70 and 12AX7 gain is 100


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