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In Reply to: RE: EL 34 for Marantz 8B posted by Michael Samra on June 20, 2012 at 11:08:24
But wait, an 8B can't use 6L6s??????????????
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I was speaking mostly of the kt66 which you may have to change a bias resistor,but I found those and the 6L6gc black plates to incredibly good in that circuit because of the good driver characteristics. EL34s are limited at a both ends of the spectrum as far as detail and even tho the mids are fine,by comparison to the kt66s an the 6L6gcs they come up short in most instances..You are talking to guy here that owns almost every vintage tube amp ever made outside of Western electrics.I have been there done that.I'm not saying to discard EL34s all together,but I have a pair of nines that I inherited that I have packed away and I also have an 8,which is similar to an 8b and both are really nice with the kt66s..I did have to change a bias resistor in the nines for added range but,it still biased el34s just fine..
THe kt77s are the best EL34 based tubes I have heard..I have everything from XF2,xf1,metal base Ampoerex, sq getter Amperex. five staple Telefunkens,4 staple RFTs,and many more such as SEDs..Here is a photo of a few..I can tell you honestly,they don't touch the Genelex kt66s in the 8b with a bias tweak.I could kid you all day long about how good EL34s are if you want me to..I have them all and you are welcome to come and test for them for yourself.THe best EL34 are the KT77s and thats my opinion..They were designed more as an audio tube and not as a guitar or industrial application tube to handle higher voltages.
When problems become increasingly difficult,we can always rely on our collective knowledge and seek relief.
Edits: 06/25/12
...the 8B was designed specifically around the EL34. Note that the EL34 is one of the few audio power pentodes where g3 is brought out to a separate pin instead of the usual practice of internally strapping it to the cathode (6L6 etc). If one looks at the schematic of the 8B, one finds that g3 is not tied directly to the cathode as it is in almost all other EL34 type amps but rather, goes thru an RC network instead. Therefore, by stuffing 6L6 types in there, one defeats this design subtlety that is unique to the 8B AFAIK. Due to how the sockets are wired, 6L6 types will work ok but the output circuit is not as designed.Persons who should know better indisdciminately make tube substitution recommendations w/o proper familiarity with the details of the amp under consideration. Bottom line: an 8B is not an ST70 and should be treated accordingly...IMO of course.
Edits: 06/20/12
AMEN!
~!
The Mind has No Firewall~ U.S. Army War College.
Roger that!
Seems like one persons opinion that all EL34 designs are no longer good means an auto substitution using these Russian mil surplus 6L6 types. Same items that have been relabeled for years by almost all commercial tube sellers...and all of a sudden their God's gift to the tube world!
Yea right! They may work but not the definitive answer to many questions.
Im not saying that at all..I'm saying if he looking for something to roll in his amp,KT66 is a great candidate,as are the 6L6gc black plates. Usually when people hunting around for tubes,they usually are looking to enhance an area of their amplifier..He can keep EL34s as I also have a shit load of them..It doesn't mean you can't try other tubes.
When problems become increasingly difficult,we can always rely on our collective knowledge and seek relief.
...with the El34 and SV83/6π15π tubes, the so-called Hazen Grid Mod. The Decware mod is just a 0.1µF film cap from g3 to cathode instead of a jumper wire as in most circuits. I don't know how the 8B's network compares in sonic effect, but there is a noticeable sonic benefit from the Decware mod with the SV83 (I haven't heard an EL34 with this trick yet.) So I agree it is worth staying with true EL34 pentodes in the 8B to keep this part of the circuit operating as designed.
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