Popped back my Tesla 4654s after a couple of months with other EL50/4654 variants. These Teslas have the same clarity/detail as the solid plate, red base 4654s, but sound more neutral. The Teslas are very accurate with excellent, punchy bass. Probably the most neutral take on the awesome 4654 sound, which could be useful for your perfect tube match, depending on the input/rectifier combination.
With tubes it is all about combinations. I already knew this, but one of my recent rolls has just confirmed it again. Also, there is not always logic behind combinations. The U52 rectifier is very clean, refined and detailed, while keeping a natural and lifelike tonality. Brimar 5R4GY or RCA 5R4GY DD in comparison sound less clear (thicker). [I prefer the Brimar versus the RCA 5R4GY DD.] So, one would think, the refined and clear U52 would work better with the mesh plate EL50, which is a bit more 'romantic' sounding than the solid plate, red base 4654. For whatever reason, the U52 works better with the solid plate 4654, offering an amazingly clear 3D space with the highest level of clarity and refinement while still sounding tonally accurate and extremely engaging: my favourite combination so far. Interestingly, the Brimar 5R4GY sounds a little better with the mesh plate EL50s, perhaps because there is a hint of brightness in the Brimar rectifier which the mesh plate EL50s balance perfectly. The mesh plate EL50s have rich and addictive tones, but don't quite have the mid and treble clarity of the solid plate 4654s.
Reflecting on the recent KT88 and KT90 discussion, I like both of these tube types. Unfortunately, I only tried the TAD bundle KT88s, but I owned the famous Ei KT90 type 2. I generally liked the spacious and balanced sound of the KT88, but preferred other power tubes to it: EL38, EL39, KT90, EL50, 4654. I still hope, one day I will have the chance to try a top-of-the-line KT88, like GEC. For a balanced and spacious presentation these could be awesome. Regarding the Ei KT90s, I really loved those. Good tonality with excellent accuracy, detail, dynamics and refinement. More detailed than most power tubes I tried. Unfortunately, they do not sound the most spacious. Soundstage is a bit narrow and the sound, while accurate, can be a bit thin and tonally not as rich as some other power tube options like EL39s for instance. They are still fantastic though, regardless.
Initially I enjoyed the EL38s, (especially for £40 a NOS pair). These sound super spacious with a lot of air and large images. Unfortunately, they are not very detailed or refined: they sound a bit hazy in comparison to other power tubes. I consider the EL39s a better version with more tonal richness. In fact, the EL39s might be the most tonally rich power tubes I have tried on the Aegis so far. I enjoyed these, but again the EL50/4654 variants offer almost if not the same level of clarity/refinement as the KT90 and almost if not the same level of tonal richness as the EL39s. The best of both worlds to me for now, but I cannot emphasise enough that it all depends on your preference (sonic and music genre) and your tube combinations for best synergy.
Venturing into EL50/4654 territories to me felt like a step up from every other power tube I heard previously. They pretty much have the detail and accuracy of the KT90, but sound more spacious, like KT88s. Tonally they are also rich and natural. Perhaps KT90 has a bit more accuracy, but EL50/4654 sound more spacious and tonally richer, more natural. This is true for every EL50/4654 variants I tried.
Tesla being the most neutral; mesh plate, red base EL50 the most romantic and tonally rich; but not quite as airy and detailed as Philips/RT 4654 solid plate. Solid plate/red base 4654s offer the clarity of the Teslas, but with a richer tonality, somewhere halfway towards the mesh plate EL50s.
I have noticed that many of the rectifiers can increase clarity and detail most of all, but some loose tonal balance in doing so. The U52 has a lot of detail and refinement, but one might find them a bit thin compared to other good and more common rectifiers like the RCA 5R4GY DD or Brimar 5R4GY. The less clear a rectifier is, the more bass quantity it seems to have: not clarity and definition, but quantity. This was the most obvious on the Svetlana winged C 5U4G rectifier. Someone recommended this Svetlana as a cheap alternative to GZ34. I have my doubts now. The Svetlana is a fun a and bassy rectifier, but when it comes to clarity and refinement it is really 'entry level'. Hopefully I will try a GZ34 metal base soon, so I can check for myself.
Combinations matter, and what works and doesn't work can be slightly unexpected and heavily subjective.
The thing is that all these tubes and tube combinations are wonderful! Rolling tubes is about refining your enjoyment, having some fun and enjoying the ride, enjoying music. Have fun, guys!
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