Nikolay sent me a matched quad some time ago. The matching process that he uses produces a very tight set, which is very important if you have a fixed bias amp like I do. Closer the match, the happier the amp – simple as that.
A little bit of a background: not only audiophile, I play guitars as well, played professionally from 1977 all the way to 1988, and now only occasional jams and studio work. So, I know a bit about the difference between 6CA7 and EL34. No, they are not the same, not even close. I will not get into the beam tetrode vs. pentode debate, nor would step into the sound-descriptive rabbit hole… Yes, they are interchangeable, however: if your amp was using 6CA7, and you want to change to EL34, set the appropriate bias. The other way around is fine, but bias for 6CA7 should be a bit higher, so it will drive EL34 quite “hot”. Some like it hot, but will shorten the life of your tubes. If you are running them in a guitar amp, especially Plexi Marshall or any decent clone of it, 6CA7 is not what you really want. Mullard EL34 xf2 is the king, but there are quite a few options that are not unobtanium. However, if at home you do have an EL34 based amplifier, you ought to try 6CA7 there. You might lose some “midrange magic”, but only in comparison to good old stock EL34 – Mullard or Amperex. RFT, which was making EL34 for Siemens, Telefunken etc. does have it too, but it is not even close to xf2/3/4. With 6CA7, you will get that ever elusive “air”, but the low frequencies… Suddenly, you will be able to hear that double or triple bass in great definition even in the late night quiet sessions. If you do have decent equipment and can not hear the difference, you may be a music lover, but not an audiophile.
I have two sets of Sylvania 6CA7 left, and their price is becoming prohibitive. I was looking for an alternative, and only EH had something promising. However, a lot of internet comments were quite categorical that it is not a beam tetrode, but EL34 pentode posing as one. Nikolay and I are still waiting for one to fail, so I can do a postmortem to physically confirm, but I can say with confidence this: EH 6CA7 is the only close copy of the original Sylvania 6CA7 beam tetrode in production today that I know of. There are construction and execution differences, and I can also see the difference in the glass. But, it is as close, arguably, as the production cost and final price allow.
They do need at least a week to “bed-in” (some prefer “burn-in”) and stabilize. Out of the box, they are a bit aggressive in high frequencies, but still missing the uppermost registers – missing on all-important “air”, or venue cues. The soundstage is not as wide and is very two-dimensional, but definition, or placement, is relatively good. However, after a few weeks, they do open up, and highs become much less stringent. Lows get some more definition and presence. Mids stabilize, and become pleasantly real, making voices quite believable. The piano sounds very real, and, depending on the recording, comes into your room. Also, EH react quite audibly to change of driver/phase splitter tubes: my amp is using three 12AX7 / ECC83, and the best result was with old stock Telefunken; they did not like old stock Mullard, the sound lost some definition, most in mid / mi-high registers. The old stock RCA set was even mushier… I didn’t even try any of the new production, most are much noisier anyway… Still, there are some things EH comes audibly short of Sylvania: old Sylvania has better balance, and highs are more clear, and uppermost range seems to be extending forever, making everything closer to the live music. While EH produces a decent soundstage, Sylvania makes it more three-dimensional, deeper. EH still clings to the speakers, making the overall image more narrowly elliptical and not as deep. Sylvania in comparison tends to explode into the room and speakers completely disappear. Also, it makes Miles’ trumpet on Sketches of Spain eerily present in your room. EH tends also to lose its composure a bit with the philharmonic orchestra in full swing; Sylvania tends to present Beethoven’s 7th, or Orff’s Carmina Burana more believably. After those few weeks, I went back and forth between EH and Sylvania, just to confirm what I heard. EH is not only a physical copy of Sylvania, it is also a “tone clone” as well. Both are very transparent to the source. Very, very transparent. I am very happy with the purchase, and I can say without hesitation that I can live with EH. In my amplifier, they are much better, much more balanced than winged C EL34. Also, they are much more quiet than Gold Lion KT-77. And regarding the volume: yes – 6CA7 is EL34 on steroids in that aspect as well.
Now, all of these observations are made in my room. Your mileage may vary, but my personal opinion is EH makes quite a good tube, so far very reliable, that is competitive with old stock, especially because of the price and availability.
Digital source: Magnum Dynalab MD801 placed on HRS Nimbus (3) / granite slab / Nordost Titanium Points, with Nordost Heimdall 1 IC and Furutech power cable
Analogue source: heavily modded / rebuilt Denon DL-103R in Transrotor Dark Star/TR800 with Konstant M1, placed on HRS R1X, with Nordost Heimdall 2 phono and power cables
Phono stage: EAR Yoshino 834P (three Telefunken ECC83) with modified power supply side, on Nordost Titanium Points / granite / edenSound brass footers, with Nordost Heimdall 2 IC and DIY power cable (DH Labs Power Plus with Furutech Rhodium ends)
Amplifier: Audiomat Prelude Reference, spikes on Oyaide SS cups / granite / Nordost Titanium Points, with Nordost Heimdall 2 speaker cables and DIY power cable (DH Labs Power Plus with Furutech Rhodium ends)
Speakers: Dynaudio Special 40 on Dynaudio Stand 20, spikes on Oyaide SS cups