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.

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. 

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 The Music Reference Forum is no longer active (Roger has moved his business from Santa Barbara in Southern California to the Berkeley/Oakland area in Northern California, where he designs and builds amps,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.

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.
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  


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.

KT-88 or EL34 doesn't matter 1%.  It's all about the overall amp design.  No point in conversions if the basic amp is not a good design to start with. 
bpoletti, you may be right. I had heard however that some, including possibly the above responders, have converted and found the EL34 to sound "better" on the same amplifier so the design wasn't a variable. On the other hand, the outlay of this type of tube amp generally is relatively straightforward. The one important variable that can truly influence the character of a tube amp IMHO is its output transformers because, as an inductor, evenness, peakiness, etc. are most influenced here. It's possible that the different loading that the EL34s place on the primary could account for the differences in sound. What do you think?

6L6GTB sweeter than EL34 - RCA black plates. 

Modjeski designed his RM-9 specifically for use with the EL34 (four per channel for 100w/per in the Mk.1, 125/per in the Mk.2), his RM-200 for the KT88 (two per channel for 100w/per at 8 ohms, more at 4!). But the 200 can also be run with KT-120’s (though not the KT-150---the transformers get too hot at the required plate voltages).
Re: Some people say that say KT88s would be "better" than EL34s. Not sure, so subjective, and like the prior note above, also depends on amp design.

E.,g I have a PrimaLuna Dialogue HP Int. Amp, and have started out with EL34s, but even in triode mode, it sounds "dry" not sweet. and even sounds a bit thin in triode and ultra linear mode. so I'm going from EL34s to KT88s for more body, texture, timbre. Case in point, its hard to tell how the sound will be with certain tubes. Unfortunately, we just have to tube roll to find out.
I googled EL34 vs 6L6 and was surprised at how much info there was on such a specific topic, including YouTube videos of guitarists comparing them. Of course the tests were in regard to heavy metal guitar amps and not critical listening but I think I preferred noromance's 6L6 recommendation. Should be fun to try since I have a nostalgic interest in the 6L6 anyway!

My question now is: how different, if any, are the bias voltage settings between the EL34 (which I think I know) and the 6L6 (which I don't know)? Are they truly drop-in replacements? Thanks, Andy

"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."

Since you already have the gear, you might as well try a vertical biamp. Remove the jumpers on the back of the speakers and use 2 channels on the amp for each speaker. 4 channels, not 2. It may make a big difference, or not. Results vary.
Thanks for your thoughts, sfall. As it turns out, I had already bi-amped these speakers in the past, more for control than for power. I had used different amplifiers and not all four from the B&K and for the following reason... To use 4 or any more than 2 channels from the B&K, you must be in the digital mode, that is to go through the amp's DSP. Although virtually indistinguishable from 2 channel, I wanted to keep my signal path pure analog which bypasses the DSP altogether.

Also, my listening room is small by most standards and the 150W per channel from the B&K's humongous power supply is an overkill as it is. In fact, to handle the myriad problems a small listening room provides, I use a 31 band equalizer to tailor the sound... particularly the bass bloat from the nearby room corners (and for minor adjustments to the rest of the audio spectrum).

You may be thinking that the Canton Karats are too much speaker for a small room and you'd be right, especially considering the smaller model speakers that are available. However, it's what I have to work with so it is what it is. Thanks again, Andy
You should be able to swap in 6L6 for EL34 as long as you can adjust the bias AND you get the GTB versions as they can work with higher plate voltages AND as long as your amp can work with these tubes in the first place. 

I thought you had a seperate multi channel amp, not a receiver.
I have the newer 3502 model that takes EL34 as well as 6550 types.  Like someone said, one tube type is not necessarily better than the other, just different.  The amp does have more bass heft with the Svetlana 6550 than the new production EL34 and EH 6ca7 tubes I tried.  One exception is the JJ 6CA7.  This is a sweet tube!  Refined and warm with plenty of bass.
noromance, yes to both. My question was (is) what is the difference in bias voltage between the EL34 and the 6L6? I found some tube specs through Google and they look close in an AB final with the 6L6 about 90% of the EL34. The problem is, I'm not sure. I would hate to break the connection, but I can always fall back on inserting a milliammeter in series with the cathode and set the grid bias by the current recommended in the 6L6 tube spec. Or... pick a bias voltage below the point where the anodes (plates) start to turn red! Probably not the best idea but it actually could work(!).

sfall, I agree with you conceptually and, as mentioned, I bi-amped my system for some time but for bass control, not for more power. I could use the digital mode with four amps since the difference in sound from pure analog is virtually undetectable. However, I listen to mostly classical music and the complex harmonics from large orchestral music are detectable (barely, but subtly noticeable, nevertheless) when processed through the DSP. As said, I have subsequently maintained control through a graphic equalizer in lieu of bi-amplification.

That's why, getting back to my original OP question, I want to improve and possibly substitute my tube amp and get back to the basics of music enjoyment. Thanks for everyone's reply! Andy8400.


I too have a PLD HP. I have read many posting and Kevin Deal also speaks very positively about using KT150s

That's the tube I am rolling next. 

psickerson what exactly are you looking to gain and are you using the stock EL34?? I have the non HP and rolled in some KT150's.  They are a nice tube and much better than the KT120 but weren't giving me what I wanted or expected.  The Gold Lion KT88 so far is working better and to be honest I think the bass has improved. Your mileage may vary but so far I've been impressed with the GL KT88.
Hi. A final word from the OP... I did end up modifying the bias circuits of the Jolida 502 to replace KT88s with EL34s (essentially making it a 302).

I LOVE the difference in sound, especially for classical music (what I listen to most) particularly how the tube amp handles complex harmonics (think of 30 violins, etc.). The only bad news is that it puts my poor B&K into question. I had assumed any subtle harshness was from my MM cartridge which has replaced my MCs (a topic for another time) but the edginess during difficult passages was significantly reduced so I'm keeping my MM cartridge but switching to the EL34 amp.

For smaller ensembles such as jazz, folk and even rock, the differences between the amps are virtually indiscernible (I installed a switch box and listened to instant, direct comparisons). Bottom line: The EL34 is a terrific tube. Worth the trouble. Thanks for everyone's input above. Andy8400

Good to hear. Now try black plate 6L6!