I've wanted to share some of this infromation for the last couple of years. I like all the tubes when they are nice and warmed up and run in they are all decent. 13DE7 gives lots of volume headroom and lower noise floor making managing the volume pot much easier. 13EM7 has to be just right with the 32 ohm and the 32 ohm does love power, just must get volume just so right!!
If 13DE7 is warm and opened up recently and a good pair of them they can sound decent and it's nice having twice the range on the volume pot for the sensitive headphone. 13EM7 was my choice the first year but eventually I figured out 13DE7 is capable it took a number of things to get 13DE7 there as they were weak and lackluster and tend to be at least my very cheap pairs that only cost a few dollars. But 13EM7 matched pair from woo is my best drivers hard to beat overall but also intense. They will put out the most punch and resolution overdriving the amp. If things arn't right electrically it is more aggressive so it can be more difficult to use when things arn't settled, when things are right there is no fatigue and very good I do like them the best. The volume is sensitive and tight so have to carefully adjust volume precisely and it's good. 13DE7 is just much easier to avoid fatigue with in those less than ideal scenarios so it feels safe to use those for these headphones. The first year I did not find satisfaction with those but I did the second year.
Recti, power cables and where you plug in the amp in can have a big effect on the WA6 SE which helped me to learn it makes it obvious with the XTC. Just dang the varience in sound from this thing from even the power cable. Other amps not as much so. I upgraded the power cable 3 times, the power cable upgrades where EPIC to me. I was using a $4000 or so clock system and I would put the power cable upgrade up there equal to that at one point. I was laughing for a couple of weeks about how good it was. Much larger and deeper soundstage and resolution, just an incredible upgrade for $250. The final cable upgrade I got was an IceAge OCC cryo treated large gauge copper ended cable and it transformed the entire amp completely and all of the tubes became much more equalized. It's like it just flowed the juice 50 percent more efficiently the amp transformed for sure! This might not be others experiences though with better AC power and it tends to all sound closer to the same at night when the power is good around here. 13DE7 and the rectis all much more on par after this. I have bad power around here so you'll get what you do out of tubes in your own situation has to be figured out and can't really be answered. If I had good AC power wow it would be less need to spend so much and make it very easy to be 100 percent satisfied if the power was like it was at night I'm not sure I'd even use an expensive clock or power conditioner, really not a need honestly I think to very much enjoy the music but this stuff helps a bunch during the day around here for me
I love warm ended rectifier the most and eventually I came to love sophia 274b which is more neutral. U52 is my best tube so far, it has notable extra dynamic and wild soundstage with power/potency, it can be harder to manage. Bass slam and punch with 13EM7 on a dedicated line is quite epic for a bass head with these headphones, huge body and lush just love it, totally engaging stuff. For slap and go zero fatigue and ease it may not be the first choice if you just unplugged your source or haven't worked out your AC power yet using a sensitive headphone to top it off on the end of the chain. It is an upgrade to the sound vs the others in a full blown setup that is stable and settled unlocking more resolution but most of the recti I've used do pretty good with various levels of roll off compared to something like the silver fox. I dont mind less resolution at all just want it sounding nice. The lesser tubes are just great for the money and I use them all and don't mind going to a less recti, in fact some of them are a go-to for some things at times and I like their rolled off darker nature (the U52 is also dark and rolled off compared to something like a silver fox at times) I use them all and love them all, they all have strengths and unique traights so I think all the tubes are good for sure besides a few really crappy cheapos! My two favorite zero fatigue safety types of tubes for the 32 ohm would be CV1863 5Z4G and an STC 5R4GY made in england for $50 and $120. These tubes are really dang good for some music listenin. CV1863 nice airy stage and maybe #1 euphonic tone, it has less resolution and just makes things easy, even if the source is struggling it makes listening to music easy. 5R4GY is more refined and elegant sounding, some just awesome midbass imaging and resolution it is the most buttery smooth tube I've seen epically good buttery factor. It does roll off the top end which can be nice for higher volume listening and I enjoy it in WA22 as well. Both of these tubes are warm tubes and darker. It's good to have a few tubes. Sophia 274b + 13DE7 is a very safe and balanced more neutral take after power cable upgrade. I liked it the least for about a year and it can be go-to now (also with 13EM7 very good). Mullard GZ34 (find a grey plate fat black base where the base sticks out 1950s also a nice tube I could work with for around $200, plump lush airy bass and imaging and low fatigue
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*Edit* PS I think the tubes you have are a great start should be good to go to a nice feel on things and keep you plenty busy for a while and no need to buy anything unless you want to
