I can give you two links...
6SJ7GT mesh - these have a mesh plate inside, as opposed to solid metal plates. As close to linear as you are likely to get with this amp.
I was thinking of purchasing these for myself but I have many pairs of these already -
https://www.ebay.com.au/itm/1449903...uid=8nvZ6vG5QIG&widget_ver=artemis&media=COPY
The 6AS7GA you can get
for even cheaper than your previous purchase here also - I have 7 pairs for myself from this site
https://www.parts-express.com/6AS7GA-6AS7-GE-JAN-Vacuum-Tube-072-612
I don't believe the 6SD7GT is compatible with the LF339.
After I received these tubes, I didn't have a chance to post my impressions for a while, but I have been listening to these tube combinations and making mental notes.
So, thank you again for pointing to these tubes, especially the 6SJ7GT mesh plate. These definitely live up to their reputation. They improve any power tube I tested with them with improved treble smoothness and overall a balanced FR.
While comparing among the TS 5998, Sylvania 7236 and GE 6AS7GA (all in conjunction with 6SJ7GT mesh), I came across some interesting observations. I tested these with one dynamic driver HD800, and one planar Audeze LCD3. GE 6AS7GA indeed worked very well with HD800, but I still found the 7236 sounding the best. GE 6AS7GA cast a wide and holographic soundstage with good bass impact, but there was still some treble harshness in certain tracks. This was resolved with 7236 and I may have noticed an increase in the soundstage depth. However, these observations are dependent on the headphone also, as I will mention subsequently.
I have a set of HD800-intolerable
tracks for testing, mostly poorly mastered albums with peaky highs. These are the ones I use for testing synergy with HD800, alongside other well-mastered tracks. They helped me to discern the differences between GE6AS7GA and 7236, which are already very good tubes.
Between the TS 5998 and 7236, surprisingly I found the 7236 still the best for HD800, although 5998 are far more expensive and highly recommended by many. I simply found the 5998 to be too dynamic and treble harsh for HD800. 7236 seems to have slightly rolled off treble that works in favor of HD800 by taming the highs and bringing out better bass impact.
Couple of notes, when I say HD800, my baseline for comparison is a Violectric V280 amp sourced from Hugo 2 using upscaled stream from Hqplayer into Hugo2's dual BNC. V280 is a top recommended amp for HD800 due to its bass impact and smooth treble. I used the same setup, only replacing V280 with LF339. I found the 7236/6SJ7GT combo better than the V280 due to the former's slightly better treble extension while not sounding harsh. This, combined with the tube holographic effect leads to a more engaging experience IMO. I think, GE6AS7GA/6SJ7GT is a close second, while TS5998 a third. I kept the 6SJ7GT throughout, because it's clearly the best input tube in my collection. My HD800 is early edition with leaner bass and higher highs (SDR mod applied), so LF339 does a pretty good job with taming treble and providing bass impact.
Now, these observations change when I substitute HD800 with the LCD3. The 7236 combo now sounds flattened in soundstage and the timbre also sounds slightly unnatural to my ears. 5998 really wins here in every aspect, soundstage, bass impact, magic of the mids, more natural timbre. It's confusing why the 7236, which had great bass with HD800, will show less bass impact with LCD3, which is bass heavier than HD800. At the end, I feel the impedance characteristics of the planar reacts differently than the HD800 with the electrical characteristics of individual tubes. Also in a OTL design, where the headphones are directly connected to the tube terminals without any buffer like transformer in the middle, the tube/headphone impedance synergy could be more apparent than transformer coupled designs, although this is my own speculation, not for sure.
and i was thinking i went too far with my 7 pairs of chatham 6as7 and five TS 5998
