I use the GE tubes Josh posted and they’re a great option. My post is around 70 on this thread. I also have extra Voskhod 6J1P-EV which I can sell you for $17. They are supposed to be great. But I found them to be unremarkable on my FX 01 unit. Your probably better off picking the 03 or one from a different brand.
I have both the suca which is the same as the FX t03 and it is like you say doesn’t add a ton of bass thickness but does add some tube qualities and eq. No I just got the aiyima tube t7 and I have yet to find someone else with it It was $99. And has significantly more internal parts I will post some here.
Extremely good reviews on Amazon. I added some NOS tubes and I think it sounds quite a bit better than the suca with GE tubes. I just got rid of my bellari tube pre amp on my headphone set up and I had no idea how much goodness it was adding until I took it away. Everything sounds dead even with the IE magni and modious DAC which some people say are warm. There was so much meat on the bone with the bellari with gold lion 12ax7.
Anyways I will be going back to the suca or tube t7 for my headphone set up I doubt it will have the meat of the 12ax7 but we will see how good the best of the Chinese pre amps are. Here are some internal pics of the aiyima tube t7.
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This one? 
Yes. I was really hoping I could get the Chinese ones to sound similar but I haven’t been able to yet. They sound cleaner and brighter but that’s not what I want. They do sound better than stock class D or solid state . And definitely do that without taking anything away . But the bellari is legit pure tube pre amp. Each tube you change into it sounds vastly different because the output is tied directly to the plate of the tube. Made in America very simple but gorgeous sounding. The Chinese ones are like 50 60% of the way there and that’s with upgraded tubes I’m going to upgrade the op amps and power supply of the Chinese ones and see if they get closer. I highly recommend the IFI power adapters
Interesting. : )
I have the FX Tube 3 with Burson opamps, linear power supply and Voskhod russian tubes. Would be interesting to compare that creation with the Bellari 
WIll have to see about shipping options to Europe and also will probably need a power supply for it, since its probably only US-spec (110V)
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yes i got a IFI power supply for it, its 15 volts. it would be a great comparison. i do think it has a lot to do with the tube type. the 12ax7 is legendary pre amp tube while the 6n3 and 565 whtaver itsnt quite as well known for pre amp . but maybe its all about how they are used internally. id love to know more about my tube t7 but no one has one yet.
I haven’t changed the opamp in mine either 
will try one day.
The PA555 uses a 12AX7 tube running at 150 volts
That’s pretty high voltage, maybe that puts more “pressure” on the tube to make it more tubey.
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possibly. i posted those pictures above of the tube t7 to see if someone can tell me what the voltage of the tubes are it seems like 105 volts which is actually quite nice for those tubes which have a mox voltage of 120 i believe at least the GE tubes do i know because i tried to put some in the bellari and blew them up with the 150 volts haha
oof lol
So I have finally gotten around to A/b testing the aiyima tube t7 with 1950s Raytheon 5670 6n3p tubes and the suca audio tube t1 with GE 5654w Jan tubes . I got to say I am surprised. The t7 is a noticeably superior device. It is about twice the weight but about the same size above you can see my pictures of the internals of the t7. It runs the tubes and I believe 105 volts. In the caps next to the tubes on the suca and fx audio t1s is 250volts But I find it hard to believe it is running that high. I’m sure someone here knows. Maybe the t7 runs even higher who knows. Either way I’m including pictures below of both internals.
The suca has a more mellow sound but don’t take that to be that it reduces the volume of the high frequencies because it does not. But the mid-range detail is unfortunately a lot less maybe it is the tubes or maybe it is a design, both are very different from each other. The sound is similar in some ways and definitely adds character to the solid state ie magni amp and he 5xx that I am testing with. Bass is nice on both however there is much more texture with the t7. Specifically on bass guitar you can hear the string vibrating or as on the suca It just kind of sounds like a bass note. It is nice to know that they are improving the design over time. I will be replacing op amps In both and adding a linear power supply in both as well and redoing the test. Also maybe upgrading the tubes if anyone knows an upgrade from the jan get tubes and 6n3 tubes I got. Although NOS rayhteon are quite good and could be the reason it’s better sounding but the GE tubes are no slouch either.
The first two images are the suca t1 same as FX t1 tube and the last ones are the t7 aiyima , notice the tubes sit on a removable board on brass spikes and says 105 on the I believe inductors? Next to sockets? They say 105 while suca says 220volts not sure of that is the plate voltage .
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It looks like your SUKA is factory stock.
This is where I ended up and I wouldn’t change a thing at this point. I began tube rolling with the GE’s and a French RT 6BA6 and kept coming back to the Reflector.
One thing I haven’t tried is swapping the op amps to see how that affects the sound.
The op amps are 1x Muse8920D and 1x LM4562. Caps are WIMA, Nichicon, and the one Panasonic in the power supply section. I have played with the values of the film caps settling on 1.5uF & 2.2uF
Tubes are Reflector 6J38P linked below.
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Yours seems very upgraded. You say you have never messed with op amps but in your picture it shows muse which can’t be stock right? I see a larger cap on the power supply . How much changes did you notice with all these upgrades?
I think you misunderstood. Both op amps were changed, by swapping I meant changing their positions, and yes I changed the p/s cap from 1000uF to 2200uF.
Tonally, the sound became richer and more detailed, clearer highs, and maybe a little more dynamic.
The biggest differences over stock were from the op amps, film caps and tubes. The other caps, not at all. Changing them was more about ensuring the values matched the label.
With these inexpensive electronic products you really don’t know how good the components are or if they’re genuine.
Last will be a decent linear power supply though I’m not sure if that will change much at this point.
nice i got the op 1656 but i can always use Muse, you like reflector the most? what do you think the main differences are from the GE? id love to mod the OP amps and tubes and power suppy to see if i can get it to beat the aiyima t7, thanks for clarifying.
I found the GE to more up front in the sound stage, where the Reflector has more depth, if that makes sense.
On the op amps, the consensus from a long long thread in another forum (AK) seems to favor the Muse, though the OPA1656 gets equal praise if you are able to solder them to a DIP adapter or are willing to pay ~$40 a pair for someone else to do it. Some are even using $$$$ Burson Audio op amps which, to me, defeats the purpose of a semi DIY budget tube pre-amp.
And then there’s the ultra modders…
A caveat here.
This is just one piece of equipment in a chain, DAC, pre-amp, amp, headphones/monitors. What’s working for me may not yield the same result with a different headphone, for example.
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Of course. Thanks for the input I was deep into that thread and about 6 months ago but there was so many pages and I had to reset my computer and I lost my place. I think I will try different op amps. Since I have three pieces of gear that take two op amps all I need are two more sets of different ones and I can exchange them back and forth. All of this is to get my Ncore and a07 class D Amps along with my schiit gear to sound more analog and tube like. I had a full tube amp setup for my speakers but I recently got some triangles towers and they just aren’t efficient enough even with 30 watts of tube power to play deep bass without distortion. So I’m back to trying to get class D to sound correct. and these little things especially with some good tubes are great for that purpose. I am also looking into modding the aiyima a07 But it seems since there are no tubes in that it will be more difficult to change the sound. Thank you for your input. I will have to give those tubes a try. Also I use the IFI power adapters and they are quite good at improving the sound of my equipment. Although those pyramid power supplies aren’t bad either
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Suca audio 
Those Chinese names are hilarious, they should hire me to come up with better ones
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So, got my Fx 03MkII with GE’s yesterday. Played with it a little, but not sure what I think yet. Used it both alone and sending a signal into my Element II. Unfortunately, the way the Element II is set up, since one has to choose either the coax or the USB, it makes it next to impossible to A/B, so you need to fuss around and change plugs, etc. I think looseness and warmth, but also made the sound feel a bit squashed, especially on the low end, with less impact in the bass in comparison with the EII as well as less separation/soundstage. It could be that the AKG K701 don’t play nice with these, so will have to try my Grado 80, as well as the Sennheiser HD6XX when they arrive. Also still need to see what effect it has used as a pre for powered speakers. Don’t get me wrong, it is still an impressive piece of kit for the price, but not sure I see a use for it for myself as of yet…
let the tubes break in, it will take away a small amout of bass detail but should do the opposite of compress the sound. remember these are cheap and therefore only about 50% or less of what a true tube amp would do like the bellari pa555 at minimum but for the price they are great. might want to try the aiyima ones like the tube t7 , its cleaner with better bass, with the tubes detailed in the post above. also a ton of modding around these like the OP-amps and power supply .