#1
I just got a tube amp from eBay and I want to change the preamp tube (12AX7) from the General Electric that it is now, to a different one. Tungsol probably.

Will I need to get my amp re biased? I have little experience with tube amps and doubt I could do it myself. But, if I just change it to another 12AX7, do I need to re bias?

Thanks
Last edited by travistag at Feb 3, 2009,
#4
It was hand made. It is an (almost) exact copy of a Fender Champ AA764, the only difference is the Sprague. It runs off of a 6V6 with a 5Y3 rectifier and a single 12AX7 pre-amp. So, just 3 tubes. VERY simple. Only volume, treble and bass, with a standby.

Sorry for leaving that out...
#6
Quote by kurtlives91
Its cathode biased...

Replace new power tube and rawk out...


Sorry, I don't know what that means... Does it mean that it doesn't need to be re biased? Or that I also need to replace the power tube?
#9
you only need to rebias power tubes. no worry on the preamp tube (which are indeed cathode bias).

Don't like the sound of the GE? Is it worn out? GEs have sounded pretty good in my past experience...Tung Sols sound good too.
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#11
Quote by kurtlives91
^He doesn't need to rebias his power tube though.

Hes got a Champ, single ended cathode bias.


Sorry, will edit for clarity:

"You only need to rebias power tubes that are fixed bias. Seeing as how you are replacing a preamp tube, which is not a power tube running fixed bias, you don't need to rebias".
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#12
OK great, I just got that same info from the seller. Yeah, I think the GE might be worn out. Actually, I'm not sure. But, I'm getting almost no overdrive at all, would that be the pre-amp or power?
#13
Preamp... but... I mean you bought a replica fender for its overdrive?
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#14
Quote by travistag
OK great, I just got that same info from the seller. Yeah, I think the GE might be worn out. Actually, I'm not sure. But, I'm getting almost no overdrive at all, would that be the pre-amp or power?



like he said^ preamp.

You mean its not overdriving when you turn it up? Cause you said it was one channel clean. That would be because those champ amps are VERY clean. My friend has one and I turned it up to 10 with relatively high output humbuckers and only got light crunch.
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#15
Right now, it goes 12AX7 > Tone Stack > 12AX7 > 6V6. If you were to make that 12AX7 > 12AX7 > TS > 6V6 you could get a fair bit of drive out of it.

You should be able to get a nice sounding overdrive as it is if you crank the MV and start hitting the 6V6 more...gets a bit loud then though, depending on your living situation.
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Last edited by DLrocket89 at Feb 3, 2009,
#16
Oh ok. I thought the pre-amp might be out. I read someone saying they thought the blew their pre-amp tubes 'cause the overdrive went out. I guess you guys are right, Champs are VERY clean. I was just expecting at least SOME crunch at full volume just because it's a tube amp. It's got none. The tone is great, though. Thanks guys, you answered my question, sorry if I ask stupid questions. I still might change the tubes just to experiment.

I guess I ignored the fact that it's a replica champ b/c the seller said "It has some good creamy distortion ala blues if you max the volume on the amp and guitar." I did so, and got next to none. I'll just settle for pedals. Great amp though, I love it.
Last edited by travistag at Feb 3, 2009,
#17
Quote by travistag
Oh ok. I thought the pre-amp might be out. I read someone saying they thought the blew their pre-amp tubes 'cause the overdrive went out. I guess you guys are right, Champs are VERY clean. I was just expecting at least SOME crunch at full volume just because it's a tube amp. It's got none. The tone is great, though. Thanks guys, you answered my question, sorry if I ask stupid questions. I still might change the tubes just to experiment.

I guess I ignored the fact that it's a replica champ b/c the seller said "It has some good creamy distortion ala blues if you max the volume on the amp and guitar." I did so, and got next to none. I'll just settle for pedals. Great amp though, I love it.



if you crank the MV, you should be able to overdrive the 6V6 really well, in a creamy sort of way. Your 12AX7 might very well be bad... *Shrugs*
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#18
Ok, yeah I'm getting clean from full volume on guitar and amp.

Thanks guys.