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Tube question?

BassGreaser

BassGreaser

Aug 22, 2002
4,013
1,663
Austin, TX
#1
I'm about ready to buy a late 60's Fender Bassman (50watt) head. It has a pair of "GrooveTube" KT66's in her. From what I understand these are really just relabeled Saratovs tubes. My question is should I plan on changing these tubes out for 6L6's or maybe even a pair of EL34? Which tube type will give me the most CLEAN power before distortion? I have already played the amp with matching tall 2x12, and I love the sound. So if anyone has any info please let me know:hmm:
 
#2
BassGreaser said:
I'm about ready to buy a late 60's Fender Bassman (50watt) head. It has a pair of "GrooveTube" KT66's in her. From what I understand these are really just relabeled Saratovs tubes. My question is should I plan on changing these tubes out for 6L6's or maybe even a pair of EL34? Which tube type will give me the most CLEAN power before distortion? I have already played the amp with matching tall 2x12, and I love the sound. So if anyone has any info please let me know:hmm:
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I think the KT66's and 6L6GC tubes are both 30 watt tubes, so if you like the way the amp sounds now, you wouldn't really be gaining anything by changing them. Don't know about the EL34's.
If I remember rightly it's best to bias the amp slightly on the cold side if you want max headroom before distortion. This also makes the tubes last longer. Bassmans sound great! :)
 
#3
There's a pretty good chance that the person who put the KT66s in there is a guitarist. It sounds like a guitar mod to me.

The amp was designed for 6L6s, so I think it sounds best with them. It should be re-biased, of course. And you might as well throw in some new preamp tubes while you're at it.

I LOVE Fender Bassmans for low-volume work. Very phat and toneful. Good luck!
 
#4
It's been my experience that if you want a cleaner vintage bassman, you need to change the 12ax7 preamp tubes to 12au7's. Works for me anyway...
 
#5
Chef said:
It's been my experience that if you want a cleaner vintage bassman, you need to change the 12ax7 preamp tubes to 12au7's. Works for me anyway...
Click to expand...

That'd be a great idea if you are you are using an active bass with a hot output; for example, my EB Stingray flattens my input valves into distortion and it sounds terrible. 12AU's would take a lot more to make them distort that 12AX7's I think.

When bassman amps were invented, basses were all passive electronics and their input sensititivity was matched accordingly. If you use 12AU7's with a passive bass, I'd doubt you'd get much volume unless it has very hot P/U's. :hmm:
 
#6
You can see from my sig line what I play. Passive PBass, and tele's drove the bassman into distortion very fast, say 2 on volume, and it was not possible to trun the bass pot on the amp up much. With the 12au7's (whic are a relative 40 gain tructure to the ax7's, I think), I can now run 5-6 volume, and pot the bass all the way up. It is also possible to substitute higher gain structure tubes, that distort less, and later, for the 6L6's if that's important to you...
 

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