Stereo 2:50 12AX7 tubes/EL34 questions

[scubidru]

A few questions here...First, has anyone noticed a singnificant difference in character with a particular type of 12AX7's when replacing the 3 tubes in the front end of the 2:50? Also, do I need to use and adapter like the THD Yellow Jackets to use EL34's? If an adapter is used do I need to select EL34 on the bias switch on the rear panel? Can I run 6L6's on one side and EL34's like a Carvin T100? I read the manual, but it says next to nothing about tube selection and the previous questions. I don't even know if EL34's will fit the same socket as a 6L6. Any help is appreciated.

 

[mr_fender]

In this application, you probably won't notice much difference, but it depends on how hot you run your preamp output. The preamp stage in the 2:50 is going to stay fairly linear (i.e. clean), unless you push it with a really large signal from your preamp. That said, different preamp tubes can always make some difference in the tone. Just don't expect it to be a night and day difference in this case.

As for using EL34's, no adapters are needed. They have the same pinout as 6L6's. Just switch the bias select switch to EL34's and plug them in. Make sure you always keep this switch in the correct position, matching the type of tubes you are using. Having it set wrong might damage the amp after a while.

Also, the bias select works for both channels at the same time. This means you have to put either all EL34's or all 6L6's. You can't mix tubes between channels in the 2:50.