tube alternatives

[basscooker]

so being totally new to tubes, i would like help deciding on things to try. my vintage tooby has a single 12ax7 and 2 6v6gt's. i like where i'm at tone wise, with my geb-7 pedal front-ending it, boosted. are there alternatives to add more breakup, like a 12at7, ..au7...ax7a...? what are the differences there? or are these going to work in reverse and be more difficult to overdrive? is a significant amount of breakup coming from the power tubes? am i spinning my wheels? just wanting to play around with tones, without frying anything.

[1958Bassman]

Originally Posted by basscooker

so being totally new to tubes, i would like help deciding on things to try. my vintage tooby has a single 12ax7 and 2 6v6gt's. i like where i'm at tone wise, with my geb-7 pedal front-ending it, boosted. are there alternatives to add more breakup, like a 12at7, ..au7...ax7a...? what are the differences there? or are these going to work in reverse and be more difficult to overdrive? is a significant amount of breakup coming from the power tubes? am i spinning my wheels? just wanting to play around with tones, without frying anything.

The difference is mainly in the gain of the tube. A lower gain tube like a 12AY7 in the first position (usually called V1) will avoid breakup and the volume will be a bit less than some of the others. The 12AX7 is the highest gain of these. If you want less breakup, don't use a 12AX7 unless your pickups are low output or you decrease the volume control setting.

[basscooker]

i'm actually seeking out more breakup. so the 12ax7's are the easiest to drive? ok i'll stick with that. like i said, all new to me. i've just seen the others and didn't know the difference.

[TylerDurdenPSSC]

I've read that passive Fender type basses driving a 12AX7 and 12AT7 in front of KT-88's or 6550's yields good, early, and aggressive break-up... At least I think I regurgitated that properly...

[basscooker]

my amp only has a single 12ax7, a pair of 6v6's and a 5y3. so i'm seeking ways to maximize the overdrive. am i right in thinking the only way to do it is boosting the signal before the amp? also there are ZERO controls (not even a volume) on the amp- it's a chassis ripped out of a powered movie projector speaker cab from the 40's or 50's. for a pic of it search Ampro in forum titles, it's a project i'm pretty proud of.

[BassmanPaul]

That configuration will only garner you in the range of ten watts, fifteen at the most. As the single 12AX7 is doing all the amplification as well as acting as the phase splitter you'll not get much gain from it. If you want to overdrive the unit you'll have to add amplification in front of it. I question whether the OPT will be capable of withstanding the abuse.

Edit: Or the power transformer for that matter.

[BassmanPaul]

Originally Posted by TylerDurdenPSSC

I've read that passive Fender type basses driving a 12AX7 and 12AT7 in front of KT-88's or 6550's yields good, early, and aggressive break-up... At least I think I regurgitated that properly...

If you are suggesting changing out the 6V6GTs for KT88s or 6550s this cannot be done. The increased heater current will toast the power transformer in short order.

[B-string]

Antique Electronic Supply yellow jacket P--YJ20 6BQ5/EL84's should provide earlier break up.

[staindbass]

i dont think you can get more gain than the 12xa7 in that socket. to use other power tubes would require extensive modification. most single 12ax7 amps are low gain, i find to get a good distorted tone i need at least two 12ax7 in the preamp stage.

[B-string]

Originally Posted by staindbass

i dont think you can get more gain than the 12xa7 in that socket. to use other power tubes would require extensive modification. most single 12ax7 amps are low gain, i find to get a good distorted tone i need at least two 12ax7 in the preamp stage.

See post #8 it is easier these days to try other power tubes.