Why do you want to swap it out? Has it become microphonic? Noisy? You want to put in a Chinese 12 A XXX something? Phillips used to make good tubes. Telefunken made great tubes. There are some decent ones being manufactured for guitar amplifiers but perhaps not as good as that original equipment Phillips? Remember the engineer's credo: " If It Works? DON'T FIX IT!" And in fact, I'm not actually certain that unit actually utilized the tube for any kind of amplification? I believe that wasn't used for amplification. It was used to merely create distortion saturation. All of the amplification is done with IC chips and transistors as this has been a standard trick of many manufacturers. Part of the reasoning behind that is that the IC chips and transistors are generally quieter, more reliable, more consistent than any tubes made today. If you want something good to swap out, go to eBay and look for some NOS (new old stock) Telefunken's. Those are my absolute favorites. And most tubes don't go bad for at least 20-40 years of operation. Just so you know, if it's not your unit, it was another similar unit where you could actually see the tube through a window in the front panel. The joke was on everybody as the tube ran at such a low voltage, it never glowed, ever, never. There were in fact 2 yellow LEDs behind it to make it look like it was actually on. In the United States, that is referred to in legal terms as FRAUD. But because it was just an audio hunk of junk, they were allowed to get away with that. It's sort of like telling you in a television commercial that you can have this brand-new car for free! (Tires are a mandatory and $20,000 option). So you aren't getting the car without the tires when you purchase it even though it's free. Titles, taxes, dealer destination charges are extra yada yada. So buyer beware. That tube may be doing mostly nothing and will never wear out. You could tell some of these things by careful examination of the schematics and power supply schematics. But if you can't read those roadmaps, you'll find yourself in Walla Walla and that's a long way from New Jersey.

So I didn't mean to talk to you like some kind of idiot. People just don't know these things. People have been taken advantage of through marketing BS, hype & falsifications.

I'm actually the Queen of England
Mx. Remy Ann David

Whoa, didn't expect a reply like that. I have no issues with the Aphex 107. It's just that I read some posts and was curious if for a very small investment I could have upgraded my equipment.

I would say to first look at the schematic. Schematics, like English are read from top left to bottom right. You will usually also find the power supply schematic semi-separated from the rest of the active audio part of the schematic. If that preamp indicates it has a full 12 V DC filament voltage than you should see the tube glowing when the unit is on. Make sure it's not a couple of LEDs sitting behind the tube. Then look to see if the power supply is generating 250 V DC? If it is, that tube is actually amplifying something. But of those voltages are not indicated it is known as a " starved plate " tube circuit. That may simply mean they are only feeding 25-50 V to the plate of the tube. And that will provide no amplification but plenty of heavy second harmonic saturated distortion. If that is what you have, swapping the tube out will not provide you with any further enhancement since it's not exactly working.

Conversely, you could pull out a couple of your 12AX/AT/AU 7 from a guitar amplifier and try those out in your 107. If you don't have a guitar amplifier, go to your local music store and purchase a couple of tubes. They're not extremely expensive. Swap it out and see what you think. I think you will hear no difference.

I don't bother with tubes much anymore. That's because they are too inconsistent and are not generally the quality level of a few-year-old Telefunken. Purchasing brand-new tubes is sort of like trying to find a brand-new Scully or Ampex analog recorder. And your chances of that are generally less than 1%

To further screw up your decision-making process, some dual triode tubes have smooth internal plates and others have corrugated & holes punched through their plates. The two sound completely and totally different from each other. Some can sound like absolute crap while others will sound like Jesus is speaking to you in person. I have units that have 40-year-old tubes in them and I won't part with those until they die. Which may in fact be after I die and I'm only 56. Heck, my Neumann U-67's have some noise in them. So about 20 years ago, I've swapped those EF 86's with a couple of brand-new Sylvania units. BARF! BIG BARF! So out they came and back went in the old tubes. I just have to make sure they warm up for it least 1/2 hour before use when they finally quiet down. And I can also safely say while this is not exactly on topic a friend of mine had his Neumann U87 modified to a 12AX7 and when he compared his brand-new 87 to my 1960s 67, he quickly realized his 87 didn't sound anywhere near as good as my original 67. Yet he had a brand-new tube in his 87. And you know the old saying a sucker is born every minute.

I like Tootsie Pops best.
Mx. Remy Ann David

FYI -
I've owned (still do, but I loaned it out and haven't gotten it back for 3 years!!!) an Aphex 107 and thoroughly enjoyed it. It's a starved plate design, but it does it (according to Aphex) differently than most starved plates. That being said, I believe it will hold only an AX7 and an AT7. I've swapped the tubes out on mine since I do have a stash of both lying around. I got significantly different sounds from different tubes and I think it's a worthwhile experiment. My best results came from a NOS Mullard 12AX7 and an old (old old stock) GE12AT7 (IIRC).
While I tend to agree with Remy's "if it ain't broke, don't fix it" philosophy, this is less of a "broken" issue than a built-in (designed that way) means of getting different colors to an already sweet (and dirt cheap) preamp!
Best-
J

Cucco, Thanks for your reply. "My best results came from a NOS Mullard 12AX7 and an old (old old stock) GE12AT7 (IIRC)" was the type of info I was looking for and most helpful. I'll check online and see if I can come across some tubes and try these as well as some telefunkens I've seen on ebay.