How to bias JJ E34Ls in a 20th Shiva? 6550s?

[richedie]

I currenty have SED EL34s in my 20th Shiva biased at 36ma and I know that is hot....might be why I get a little bit of mud in the tone. Bogner recommended 29ma but I think that is low.

I have a set of JJE34Ls and I want to try em tonight but need to know how much hotter to bias them over regular EL34s???? Thoughts?

I also want to try 6550s. Anyone know what I do to get 6550s to work in a 20th Shiva?

Thanks!

 

[se7en]

Yeah, that's why I was telling you about the bias drift. 36 ma might sound good at lower volumes, but once you turn it up it may get muddy. 29 ma sounds right. As far as where to bias your tubes? Here's an easy way to calculate plate dissipation: http://www.webervst.com/tubes1/calcbias.htm. I always found 34L's to be a bit muddy naturally, so not sure they'd be your best bet.

 

[richedie]

Yeah, that's why I was telling you about the bias drift. 36 ma might sound good at lower volumes, but once you turn it up it may get muddy. 29 ma sounds right. As far as where to bias your tubes? Here's an easy way to calculate plate dissipation: http://www.webervst.com/tubes1/calcbias.htm. I always found 34L's to be a bit muddy naturally, so not sure they'd be your best bet.

Really? Eurotubes says the E34Ls will be more aggressive and fuller sounding, bigger sounding. Maybe I should leave the SED Winged Cs in place.

Still confused on the bias drift because all amps do that and most manufacturers bias EL34s much higher.
Maybe I will do 30-32?

 

[se7en]

Yeah, that's why I was telling you about the bias drift. 36 ma might sound good at lower volumes, but once you turn it up it may get muddy. 29 ma sounds right. As far as where to bias your tubes? Here's an easy way to calculate plate dissipation: http://www.webervst.com/tubes1/calcbias.htm. I always found 34L's to be a bit muddy naturally, so not sure they'd be your best bet.

Really? Eurotubes says the E34Ls will be more aggressive and fuller sounding, bigger sounding. Maybe I should leave the SED Winged Cs in place.

Still confused on the bias drift because all amps do that and most manufacturers bias EL34s much higher.
Maybe I will do 30-32?

I'd agree with that. JJ's in general sound muddier to me in dark amps. In bright amps they make more sense to me.

I'd just try something lower and test it out 'at volume'....adjust it till it's where you want it...how hard can it be?

 

[richedie]

True, maybe I can just adjust and play, LOL.

Maybe Bogner knows best, they are the ones who sent me the amp with Winged Cs.
I know Tung Sol EL34s are killer though!