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KT-88 vs. EL34

Hi. I have a modified Jolida 502 amp (not my main amp) currently using KT-88s and formerly the similar 6550s. Some have suggested that this unit will sound even better, power hit aside, modifying to accept EL-34s. The mod is easy. Anyone find this to be true or is it just another myth? Thanks in advance, Andy8400.

andy8400
sfall
346 posts
 
I wouldn't say better, its more like different. 6550's and KT88 have a more "modern" sound to them. Highs are more extended, and bass has more definition. EL34's tend to focus more on the midrange. Keep in mind that I'm talking in general terms here. There's always exceptions.

If the amp was modified, do you know if its wired in triode? It makes a nice difference. 
bdp24's avatar
bdp24
10,097 posts
 

Roger Modjeski of Music Reference and RAM Tube Works had for quite a while a forum on AudioCircle. On it he discussed tube amplifier design, tubes themselves, and the relationship between tube circuits and the performance characteristics of specific tube types---how the two are interrelated. The Music Reference Forum is no longer active (Roger has moved his business from Santa Barbara in Southern California to the Berkeley/Oakland area in Northern California, where he designs and builds amps, an ESL loudspeaker, and a subwoofer. He also teaches a course in amplifier design.), but remains readable on the AC site.

There is a LOT of information about tube circuits and tubes on the old Audiocircle MR Forum, well worth your time to peruse. Roger invented computer tube testing and matching, and is the world’s foremost authority on vacuum tubes. He’s not easy to reach by phone, but if you do you may be able to get a lot of your questions answered straight from the horses mouth.

jond's avatar
jond
5,974 posts
 
I will say I personally very much dislike the 6550 tube from past experiences. I am a bit EL34 fan and find a nice balance in that tube of SET-esque richness and modern linearity. Particularly for me the Gold Lion KT77 variant has been a tremendous find and is my power tube of choice for my EL34 amp. Also I agree with sfall above circuit matters a lot my amp is triode wired and class A which is why I find it so rewarding.
rar1's avatar
rar1
1,811 posts
 
Hi Andy -

I would make the case that this is very speaker dependent.  As you may be getting from the other posts, the sound is different as opposed to necessarily better or worse.

Are you still using the AR 4s?  For the longest time, I had the AR 302s as my speaker (latter day AR 5s).  When I used KT88s and 6550s, the sound was more fleshed out, with more force.  The EL34 sound was more delicate & balanced & intimate sounding.  The KT77s and 6CA7s seemed to get the best sound for me.  My amp was (still is) a Prima Luna PL5  

Rich  


andy8400 OP
58 posts
 
First of all, thank you for your replies. I will address all of your questions to date. 
1. Amp is wired as a pentode (or tetrode, depending on how you view beam power tubes) and not triode. Often thought of triode wiring and even single ended using one of the tubes but the power hit would be too great, maybe.
2. Not using AR4x. Those were my wife's college grad presents and have been out of sight for over 50 years (we just celebrated our 50th anniversary). Hooked them up for fun and they worked!
3. I am currently using Canton Karat M70s, woofers facing out. Not too efficient and 6 ohm average. Current amp is SS, a B&K AVR-307 (150w x 7) in two channel analog mode, used for stereo only. I like switching in the tube amp however; its intrinsic linearity is a pleasure to listen to. No edginess (but a little bright). Based on everyone's good advice I would really like to try the conversion to EL34/KT77s. a few resistors and Jond's 4 Gold Lion tubes and I'll be set to go.

I will try to track down the old A-C forums to learn more; Thanks for the suggestion bdp24. Andy8400.



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