I know - that's what's on them. Each heatsink is two fins with a flat bit between and those MOSFETs on them.
Nothing on the red ones which are connected to the green ones (IRF630 MOSFET) with those brass things. So you must mean the blue ones? They are LM317 , 3 Leg adjustable voltage regulator. https://www.ti.com/lit/ds/symlink/lm317.pdf?ts=1629093919807&ref_url=https%3A%2F%2Fwww.google.dk%2F I think eventually you will have to come to terms with the valve actually doing something! - I know you really, really don't want to but you've run out of components now.
Begs the question: what are the FETs there for? They’re not part of the power supply. If the valve’s doing the work, it would presumably be connected as a single-ended triode on each channel and even if you could get sounding not-horrible due to the low HT voltage, you’d still have a significant impedance mismatch between the anodes and the (relatively) low-impedance headphones. I reckon Johnny Chinaman’s pulling the wool over your eyes
The solid state stuff will probably be a combo of regs for the heaters (LM317) and constant current sources the valve's cathode.
The FETS are probably class-A output stages using the two big resistors that are stupidly above one another and discolouring with the heat they produce. The FETS are on double heat sinks because they need a good heatsink. The valve is acting as a preamp for the output stage. Of course, swapping out the valve for another couple of MOSFETS you wouldnt hear the difference, as their characteristic curves and non-linearity is quite similar. Low feedback around amplifying stages, leaving nice second harmonic distortion. I found one modder who didnt realise the ECC83 is a 12.6 volt heater valve , so they went mad dropping the voltage to 6.3 volts .. .
ECC83 has a center tap, so you can run it at 6.3v, if I remember correctly, it's been a while. I only see one big hot resistor, could it be a long tail pair, possibly? My money is on the Fets being a poor man's constant current source, but I don't gamble.
This is what it is. It's an impedance smoothing "buffer" thingamy jig... I think. Whatever, due to the mismatching headphone/headphone socket in my audio interface it sounded brittle and horrible and now with this snake oil container in between it sounds smoother and has gained sub-bass in the phones that I couldn't hear before. It should be noted that 99.9% of recorded music, including classical music, jazz music and all kinds of music we regard as "clean" is deliberately distorted in the studio. There are sooo many effects to add this subtle (and not so subtle even in clean music) distortion you would scarcely believe it. Why is that? Because 100% of humans in listening tests like it. Madness on one level but it's a fact! Digital recording is too clean, clear and precise for most people's ears to be comfortable with for long. It's hard to put your finger on why, but if you listen to a record you enjoy it. If you listen to a digital recording, despite it's super clarity, IDK about you but I'm not relaxed by it in the same way and loose interest/switch it off. Something it the brain, I can't hear any difference however hard I try. So maybe this thing also distorts the sound as well as sorting my impedance mis-match. Whatever, it does change it very obviously, it's "warmer" (distorted). ha-ha-ha.
There are indeed two resistors one above the other but I just had a good look and they are not discoloured by heat at all - perhaps a trick of the bad photo.
It's ironic that after decades of engineers doing all in their power to reduce distortion while using tape in the studio and spending inordinate amounts of money to do so - now that they have that perfection they always dreamed of... they are spending inordinate amounts of money and time and effort to emulate that subtly distorted tape "sound".
Google tape emulation vst, or saturation vst, or clipper vst. Then select "images" and scroll through them.
That is ever the "human condition". I am reminded of your point about room conditioning, when we do a show, we take as much room conditoning that will fit into the van with us, yet most folk entering the demo room, don't comment on the odd looking diffusion panels but how good the speakers sound (without thought to my mate's excellent electronics either). Very frustrating, the shows simply become brand awareness, tho they are a chuffin good party.
You'll know this... There are only 2 private speaker reviewers in the whole wide world who offer real honest data. To do it, they had to spend $100,000 of their own money on the test rig. A Klippel nearfield scanner. One is Amir Majidimehr (ASR) and the other is Erin's audio corner. The vast majority of speaker manufacturers/designers do not have this test gear! Some rely on decades of successful marketing, some just lie. If they put out figures, they all use different methods to assess them. There are £200 speakers out there that perform better than £2,000 ones. I'm glad I'm not into hi-fi, more effort has been put into car hi-fi and car hifi enthusiasts are better educated technically because it's so difficult.
I count myself as a good friend of the chief engineer who designed the latest audio analyser at where I work, called the U8903, it's a couple of years ago now... He told me he enjoyed the project but didn't think it would sell, despite it having a noise floor that was equivalent to a fart in thunder! Why wouldn't it sell, I asked? He said hifi designers don't want perfect, they want a level of broken, I suppose you could see it as wanting a "house sound", his point was, it wasn't the pursuit of science anymore, just marketing
Hahahaha, yep, speakers, the hifi component where it is actually worth spending more on the box than the marketing budget, but nobody does. I enjoy the hifi industry, but mostly for the people, the technical mendacity is appalling, some of the people in it are the biggest party animals, I know It's quite scary, in a good way, for an R&D engineer to be exposed to these folks, gets me out and stops me being a complete geek
There is a vague brownish tint to the centre of the resistor. That is a resistor reaching the point where the coating is beginning to char. Try sizzling a finger tip on it when its on !. Colour code blue grey black gold brown (6.8 ohms, 1% tolerance) . If its a Class A amplifier with two channels stuffed in a tiny box, it deserves to run very hot.
