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Preamp broken

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This thing is weird.
And you are not wrong. there either.

The whole thing screams "gimmick" to me. Having had a look at the full schematic the actual "preamp" in the thing is transistors and IC amps; and the audio outputs are driven by IC amps.
The valves may be in the middle of the circuit but do not appear to do anything essential or even useful.
 
Just for info, these are some rather older and larger valves, the originals in a 1950 recorder I've been working on recently.
The filaments, cathode tubes and general structure are rather more visible in these:

IMG_4092.jpg IMG_4095.jpg
 
Just for info, these are some rather older and larger valves, the originals in a 1950 recorder I've been working on recently.
The filaments, cathode tubes and general structure are rather more visible in these:

View attachment 131578 View attachment 131579
Well I originally thought somewhere along the way power wasn’t reaching the tubes, but I guess it’s something else. Those tubes do look a whole lot brighter.
A friend of mine has two vintage reel to reels. With visible tubes and they get pretty warm!
 
Those tubes do look a whole lot brighter.
I shaded the area before taking the photos, so the filament glow was clear. I think your photos were just in brighter ambient light so the filaments did not stand out so much from the background.

Re. voltages, you need to check the anode and cathode voltage of each valve section as well - the filament supply being on is a good thing, but that alone does not mean they are working.

If both channels failed simultaneously I'd look at power supply voltages before getting in to details on the audio path parts.
 
The valves may be in the middle of the circuit but do not appear to do anything essential or even useful.
they are in the signal chain to impart "tube sound" into the signal, and the current mirrors are there to linearize the output of the tubes beyond what you normally see in tube preamps, so they are adding a very slight "tube sound" without adding enough even harmonics for you to pick it out as distortion.... i'm sure the resulting change is measurable on test equipment, but so subtle that in a listening test you would hear a difference, but not be able to pick out what the difference is.

the current mirrors also act as level shifters so they can direct couple the plates of the tubes to the op amps without the phase shift of capacitive or transformer coupling.
 
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the current mirrors also act as level shifters so they can direct couple the plates of the tubes to the op amps without the phase shift of capacitive or transformer coupling.
I feel an opportunity to be educated here. Why would they want to remove the phase shift? Surely it would be near enough equal for both channels to not be noticeable anyway if they just used Cs or Ts?
 
I feel an opportunity to be educated here. Why would they want to remove the phase shift? Surely it would be near enough equal for both channels to not be noticeable anyway if they just used Cs or Ts?

I doubt they do - it's probably just advertising bullsh*t, rather like pointlessly adding valves.
 
it's probably just advertising bullsh*t, rather like pointlessly adding valves.
i wouldn't be surprised if some ad brochure for this preamp actually said it's a "DC coupled tube preamp" or something like that.... "audiophiles" are a highly opinionated bunch. some of those opinions are valid, but i've seen a lot of downright "snake-oil" stuff out there (very expensive snake-oil). one company makes preamps with a huge 50 lb power supply because their claim is that even for a preamp, the power supply needs to have an impedance of less than a milliohm or it will degrade the sound somehow.... and don't get me started on the "cryogenically decrystallyzed" audio cables or the "no electrolytic capacitors in the signal path" nonsense.....
 
i wouldn't be surprised if some ad brochure for this preamp actually said it's a "DC coupled tube preamp" or something like that.... "audiophiles" are a highly opinionated bunch. some of those opinions are valid, but i've seen a lot of downright "snake-oil" stuff out there (very expensive snake-oil). one company makes preamps with a huge 50 lb power supply because their claim is that even for a preamp, the power supply needs to have an impedance of less than a milliohm or it will degrade the sound somehow.... and don't get me started on the "cryogenically decrystallyzed" audio cables or the "no electrolytic capacitors in the signal path" nonsense.....

There's a lot of gullible people out there, and many dishonest companies happy to fleece them.
 
This https://www.thecableco.com/gtx-d-g-duplex-pure-copper-receptacle-w-gold-plating.html one is good too.
1623784837358.png

Of course everyone would love to make pure-copper receptacles, but its malleability –lack of stiffness – makes pure copper a poor choice. That’s why you’ll find phosphor bronze or brass in some receptacles. Furutech’s intense engineering scrutiny has resulted in an industry-first, a technique allowing us to use special Furutech 24k gold- or rhodium-plated α (Alpha) pure copper conductors strengthened and sprung by our innovative nonmagnetic Stainless Steel Conductor Spring System that keeps a firm grip yet won’t damage male connector blades or their plated surfaces. Even the screw-down pressure plates are curved to maximize contact area. The GTX receptacle can be summed up in a word; virtuoso!

Feel, experience and communicate with music and sound!

-Rhodium or gold-plated α (Alpha) Pure Copper Conductor (0.8mm thick)
-Nonmagnetic stainless conductor spring system for pre-tensioning and superior grip
-Body material: Nylon/fiberglass with piezo ceramic and carbon damping material
-Cover material: Polycarbonate
-Parts set with nonmagnetic 2.0mm-thick stainless brace plate
-Specified for wire diameters of up to 4mm (approx 10 gauge) w/high-torque set screw tensioning
-Specially designed patent-pending conductor pressure
 
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