So I bought one of these. Realizing that the whole "tube" section might be fake, I still bought it. It's not like I paid $1000 for it, lol.
I know a little about electronics and a little about tubes, but I'm not keen on reading the circuit boards to see if they are actually somewhere within the amplification chain. I know the two outer 6E2 tubes are just for show as lighted VU-meters to depict input levels, but the two inner 6N3's and 6N5P in the back supposedly in the amplification chain.
Any armchair internet EE's care to tell me if this headphone amp does what it say it does? I know of the "remove the "tubes" trick and have yet to do it since it is in my office at work, but even then I don't "trust" that trick because perhaps there is a jumper of sorts at work when the tubes are inserted to make it seem like it "passes" the trick.
That is a stock photo from the sale, but I can open it up if need be.
I know a little about electronics and a little about tubes, but I'm not keen on reading the circuit boards to see if they are actually somewhere within the amplification chain. I know the two outer 6E2 tubes are just for show as lighted VU-meters to depict input levels, but the two inner 6N3's and 6N5P in the back supposedly in the amplification chain.
Any armchair internet EE's care to tell me if this headphone amp does what it say it does? I know of the "remove the "tubes" trick and have yet to do it since it is in my office at work, but even then I don't "trust" that trick because perhaps there is a jumper of sorts at work when the tubes are inserted to make it seem like it "passes" the trick.
That is a stock photo from the sale, but I can open it up if need be.
Can you elaborate a bit please? I certainly see a lot more than "just the tubes", but I wouldn't know if the rest of the circuitry is actually responsible for driving the headphone/RCA outputs. These Chinese "tube" amps are notorious for deceiving schmucks like me, so I want to make sure I am a schmuck! 
I see what looks like a TO92 package transistor between the red and blue wires coming of the mains socket. I also see a 28 pin surface mount IC and a multi lead flat-pack surface mount IC below it. And just below that what looks like a dual transistor package. Or perhaps a crystal. I wonder what they're doing.
There are chips like that capable to drive 600 ohm headphones by their own! But they would ask for robust input signal. Amp's specs and a closer photo of this chip would help.
Edit; This is a DAC. The tubes are probably working.
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All those tubes and just for show? Unlikely. It doesn't make sense economically. Might as well put those tubes to use, especially since it has 6N5P. We are seeing huge 15W resistors most likely for 6N5P cathode follower load. I'm betting it's the usual grounded cathode gain stage DC coupled to cathode follower not unlike Bottlehead Crack amp (google for schematic). The position of the chip also doesn't make sense if it is for headphone output duty.. BUT then again it's Chinese sooo who knows there is some SS headphone amp underneath that "transformer cover".
I believe that the tube amplification chain is genuine. This amplifier is sold by different brand names and case styles, even as bare board without the case. The picture on the first post is the "deluxe" version, with the 6E2 vu-meters, aluminium front panel, output relay to remove the turn-on noise, and nice transformer cover. The 50VA toroidal transformer probably has a 6.3 + 3.15+3.15 and 170V secondary windings, according to other pictures of the product. I was tempted to buy this amplifier myself, but I saw 2 fatal flaws.
a) the long term reliability is dubious. The power resistors are next to the electrolytic capacitors and right under the (undersized) transformer. They probably are small, low-grade computer-supply type capacitors. On a similar compact China-sourced tube board, I had to replace all the filter capacitors after only two years because they were damaged due to overheating. In a OTL circuit like this, a electrically leaking output capacitor means DC on the headphone (it may be destroyed).
b) I am not really convinced that a single section of 6080/6N5P in OTL mode is enough to drive a low impedence 32 ohm headphone. Has anyone actually tried this?
After adding the import fees, this is not a cheap amplifier anymore, at least according to my back-of-the-envelope calculations. Final cost is about the same as all the parts for a traditional 6080 + ECC88 amplifier of this kind plus a separate China-sourced small USB DAC board (that I don't really need, actually).
a) the long term reliability is dubious. The power resistors are next to the electrolytic capacitors and right under the (undersized) transformer. They probably are small, low-grade computer-supply type capacitors. On a similar compact China-sourced tube board, I had to replace all the filter capacitors after only two years because they were damaged due to overheating. In a OTL circuit like this, a electrically leaking output capacitor means DC on the headphone (it may be destroyed).
b) I am not really convinced that a single section of 6080/6N5P in OTL mode is enough to drive a low impedence 32 ohm headphone. Has anyone actually tried this?
After adding the import fees, this is not a cheap amplifier anymore, at least according to my back-of-the-envelope calculations. Final cost is about the same as all the parts for a traditional 6080 + ECC88 amplifier of this kind plus a separate China-sourced small USB DAC board (that I don't really need, actually).
While you are at it, check the path from the earth pin on the power socket to the chassis. On a different amplifier of this kind that I bought on ebay from China, I found that the protective earth conductor from the socket to the circuit board had a smaller section than the live and neutral conductors (a electrical code violation), and worse: this trace on the circuit board was not actually connected to anything, and the metal chassis was not earthed (a code violation and safety issue). The metal bottom chassis cover should also be electrically connected to the other chassis parts. This is not a given on this kind of devices. I had to scrape the paint under a screw to get the contact.
A clear picture of the integrated circuits and the capacitor markings would be useful to evaluate the circuit.
A clear picture of the integrated circuits and the capacitor markings would be useful to evaluate the circuit.
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