Changing EL-34's to 6550 or Kt-88's


I have a Conrad-Johnson Premier 4. It has 8 EL-34's with individual bias contols for each tube, It is a large amp that wieghs 82pounds and is 100wpc. I have seen adds of amps for sale and they say that the amp can take EL-34's, 6550's or kt-88 and soforth. So is it as simple as just switching the tubes and resetting the bias? What is the benifet of switching, more power? or better sound?

I can't address your amp specifically as I have no experience with CJ, but my Quicksilver Mini Mono's can take all the tubes you mention and are auto-biasing. As a broad generalization you can count on getting a bit more UMPH in the low end with KT88's and generally a fuller sound. Going back to EL-34's may be difficult at first as they may sound 'thin' in direct comparison, but can be very musical and detailed at the same time. Which is "better"? That is really up to you. YMMV and your preferences and room and system will have tremendous impact on which works best for your ears. For me, I prefer the KT88's in my Mini-Mono's. If your amp is manual biasing then you obviously you would have to re-bias for the different tube (or for any tube change for that matter). But do check someone who knows your amp to make sure that the circuit is designed to use all those tubes since many amps are not.

Contact CJ. They tend to have a very strong opinion about which tubes their amps were designed for.
Keep in mind that changing to different EL34s will change the sound too.
I agree with Elevick. My Jadis JA80s are auto-biasing and can accept all of the tubes you mention, but not all amps can do the same; I don't think the CJs you have can take other types of tubes, but they can give you the answer better than I.
I have had the PR. 5's which are the monoblock version of PR. 4. It can only take EL34's in stock form. You would not want to switch anyway - EL34 is far more musical than 6550s and the like. In fact, CJ offers a mod on their top of the line Premier 8 to convert it to EL34s (this is an upgrade... their normal configuration is 6550s), for an extra few grand $.

Send it to Bill Thalmann (orig. designer from CJ, ) and have him do his magic on it. It will be much improved vs. stock. Change out the 5751s and 6CG7 for nice minty NOS tubes and you will have quite a decent amp overall.

If the power of EL34 is adequate, you will find them to be a bit more pure sounding and musical than KT88 and 6550, or, at least I have in my experience. If the power is not adequate then EL34 will sound thin, and you'll need KT88 or 6550 powered amp. These can produce excellent sound as well.

I am using the conrad johnson Premier 4 to drive the ribbon mids and tweets on my Infinity RS-1b's. So basicly the El-34's are my best bet for sound quality since I have another amp driving my woofers.

Thanks for the help.