Having spent a good while with these wonderful tubes, I am ready to share my impressions and comparisons!
Power tubes comparison first, which I listened to with the National Union grey glass 6SN7 as driver. The NU has a very distinctive warmth, great bass depth and super smooth treble tone characteristic of NU tubes. More below where I compare it a little to the GEC inputs
GEC 6080 + NU 6SN7
Compared to the 6AS7 and CV4079/A2293, the GEC 6080 is definitely the smoothest and easiest to listen to. Its excels the most in the mids, where it imbues the music with amazing warmth, tonal colour and soul- the GEC sound. It also has the most rolled off treble of the three, which definitely serves to enhance the definition and prominence of the midrange. Vocals sound natural and effortless, and I believe that any music that aims to portray the human voice would benefit greatly from this combination. The upper-bass and lower-mids are well textured and dynamic, but the bass is very relaxed, and could benefit from a little more attack and extension. These had the most bass bloom, which contributed to the smooth and natural tone. If listening to more complex music, one may want a bright input tube with quicker attack and bite to avoid sounding too sluggish. The treble is airy and well defined, but noticeably rolled off when compared directly to the other power tubes. It is also a little dry and possibly thin at times in the top registers, but only in comparison to the lushness of the rest of its frequencies. Overall, although there is a lot of warmth and midrange presence, the sound does not tend to linger- notes seem to fade a little faster than natural- giving a sense of smaller acoustic space. This presentation can be beneficial especially in bringing the mids forward to create a more intimate soundstage. I think the 6080 can add appropriate warmth to a bright driver, and is definitely the best tube out of the three for pleasant laid-back listening, easily enjoyable tone, and warmth without sacrificing much in terms of technicalities.
GEC CV4079 + NU 6SN7
The gain of these tubes is a bit higher, so I made sure to listen at various volumes, and only note differences that were still clear at audibly lower volumes. Note that these are the 'newer', grey plate ring getter versions, and I have not heard the older black plate/square getter A2293 versions which are supposed to sound a bit darker.
The first thing I noticed was an immediate step up in clarity, extension and tightness of the bass. There was also a major boost in upper mid and treble energy- the treble was more prominent, extended and airy, with impressively sparkle. This created a very dynamic presentation- attack of notes were more immediate, but also a little dry sounding as a result. The enhanced treble also gave a better sense of soundstage, especially in depth, and separation. Overall, these are definitely more detailed and push the mids more front and centre than the 6080, making it sound almost a bit veiled and slow in comparison. A very clean sounding, highly resolving tube, great for complex music, reminding me of the TS 7236 but with the GEC bass and midrange tone. In my notes, I summarised the following comparison; detailed, technically proficient, accurate CV4079 vs. intimate, romantic, lush 6080.
GEC CV2523/6AS7 + NU 6SN7
The 6AS7 bass is of similar quantity and extension to the CV4079, but with slightly more bloom. It delivers a warm, enveloping sound, stemming from this controlled bloom in the lower mids/upper bass. Midrange is somewhat forward (not as much as the CV4079- like sitting a few rows back vs. front row) and exudes the GEC sound like the 6080, rendering it incredibly refined and smooth. These mids are my favourite for having the richest and most detailed sound, but are actually pushed further back into the stage, I think because of the increased energy in the frequencies around it (upper bass / lower treble). The 6AS7 definitely has the most energy in the upper mids and lower treble, making the overall presentation lighter, more transparent and refined without sacrificing any warmth and body from the low end. The treble is also appreciably smoother and less aggressive compared to CV4079. It also seems to extend a touch further, with really sparkly yet non-fatiguing details. I found the imaging and sense of stage to be more accurate as well- there is a clear sense of 'layers' in the sound in complex passages, which is less immediately obvious for the other tubes. There is a lot of detail, particularly microdetails, tied together coherently with a natural and expansive tone. Overall, there is a sense of restrained gentleness, but with the ability to generate lusciousness on demand. Compared to the CV4079, over all its frequencies, it sounded just a touch less forward and technically precise, but with a more airy, elegant presentation that was more tonally pleasant and musical.
I then swapped over to the TS 5998 in order to compare driver tubes; this allowed me to make a comparison between the 5998 and GEC 6AS7 too.
TS 5998 + NU 6SN7
There is noticeably tighter and bigger bass than the GEC 6AS7. The lower end is what I think the 5998 does best, giving a really deep, warm sound without sacrificing any detail or quality of attack. The treble is a touch more rolled and warmer, but again managing to convey all the microdetails effortlessly. Overall, the 5998 seems to have slightly better technicalities (perhaps due to more emphasis in the extreme lowest and highest registers) and sound 'faster' in its attack and clarity, while still adding dollops of warmth across its frequencies, particularly warmer than the GEC in the upper mids. The warmth does make it a bit less delicate and airy sounding, in exchange for a more powerful, dynamic and punchy presentation. I found it had a similar tonal presentation to GEC 6080, but with better speed and technicalities across the board especially in its sense of warmth and decay, giving a better sense of grandeur and space. The GEC 6AS7 had bigger soundstage still (a little in width but especially in depth), with even more air and space/separation between instruments. Overall, the 5998 presentation is euphonic with lots of microdetail, and slightly warm of neutral. It again excels on vocal heavy music, but I found it to be not as tonally accurate as the GEC 6AS7 for acoustic instruments. With a slightly more rolled off treble and higher gain though, I found I was able to turn up the volume more to hear more microdetails without the overall presentation being too loud. Compared to the 5998, the TS 6080 which more may be familiar with is very similar in tone but more aggressive in the treble and with weaker bass.
A comparison of the GEC driver tubes, paired with the 5998.
TS 5998 + Grey glass metal bass L63
These are much more resolving and transparent sounding compared to the NU. Overall, there is a lighter and airier sound with incredible levels of detail, but the mids are drier with less lushness and richness. These L63 have a very similar tonal presentation to the GEC 6AS7, with a great deal of treble energy and detail readily available. I would personally want an even warmer power tube to tame this energy. Nevertheless, the warm treble of 5998 matched quite well with the airy transparency of GEC treble. The soundstage of this combination was veritably huge in all directions! While the midbass was strong, I found the bass to be a little lacking in extension, quality and texture compared to the NU- a little polite sounding and not enough to offset the enhanced treble energy.
TS 5998 + Grey glass ST shaped L63
These are the older shouldered glass L63. I found the mids to be much more engaging and resonant, being brought more forward with more warmth. There was no sense of dryness that was apparent with the metal base. The treble also sounded sweeter with more presence without excessive brightness- the top end in fact is the most rolled off of the three input tubes. The overall presentation was slightly less aggressive, smoother and with more enjoyable tone and fuller sound. Imaging also seemed slightly more accurate with each instrument occupying a more defined space, and tracking singers moving across a stage was noticeably more precise. Perhaps most enjoyable was its greater dynamic range- soft notes in particular were more gentle without being inaudible. The bass was bigger with more resonance and decay, slightly better texture and attack, and definitely deeper extension. I found these tubes fetched more microdetails from the music, especially noticeable in complex orchestral passages, while retaining a balance of tonalities true to the instruments and their acoustic space.
TS 5998 + brown base L63
The bass texture and extension of these are as good or even better than the ST shaped L63. There is increased clarity and tightness across the whole frequency range, with the treble being more forward with lots of detail, but without the dryness present in the metal base L63. I believe this one pairs better with the TS5998, being not as warm as the ST shaped L63 which would benefit from a power tube that is a little more neutral or transparent. There was more apparent weight and complexity to sound with more air and space, while retaining an airy and spacious presentation. Overall, it has the detail and technicalities of metal base, with a tone more similar to ST glass- the treble is certainly very strong but not as prominent as the metal base. I would liken the brown base L63 to the brown base GEC 6AS7, and the grey glass ST shaped L63 to the GEC 6080 in terms of tone and overall presentation.
Having listened to all these tubes and understood the characteristics a little better, I think that the 'too much GEC' problem can occur when too much upper end detail and airiness is combined together without appropriate bass and midrange warmth to support it. The combination of the 6AS7 with the ST shaped L63 based on my notes seemed to be able to avoid this problem, and listening to them proved my assumptions to be true to my ears. It had the best presentation overall for me judged in terms of combined tonality, technicalities and enjoyment of the music. I believe this was also Glenn's favourite combination!
I have had a great time playing around with the GEC tubes, and although my comparisons above make it seem like there are huge differences, in reality their overall presentation and tone are all still quite similar! I'm ready for a change of pace and will be listening to some beautiful 6C4 tubes which have arrived from
@Velozity. They are in top condition and were wonderfully packed. Anyone thinking of buying tubes from him, buy with confidence! A small comparison of the 6C4 tubes will be in the works as well
No. I didn't know there's a high end Odyssey brand and that sure look impressive but those are speaker amps with solid power and impeccable finish. My amp will be made by Ultrasonic Studio in June.
