What could be the Filter capacitors of this circuit?

What's the hum sound like? Buzz is unlikely filter caps, and hum is only going to be filter caps if it's 120Hz hum. Download on audio oscillator app on your phone.. set it to 60Hz, then set it to 120. Which one sounds more like the hum you're hearing? If it sounds more like 60Hz, you're chasing the wrong problem by wanting to change the filter caps.
 
I have no idea how to figure out. What could be the filter capacitors of this amplifier circuit? it is an tube hybrid called Qinpu Q2. I hope to fix the hum / buz it has by replacing the filter caps.
Max, is right. Why do you want to throw good money after bad? IOW, without a good idea of the problem you have, just changing the power supply caps is just a shot in the dark.
One would suspect the PS caps if the unit was older than say 5 years or after 2 to 3000 hours of use. Or there was an over voltage incident which may have ruined the PS caps.
If this is a new unit why can't you return it or at least get the seller to give you a schematic or a replacement. good luck
 
Really hard to tell just by a picture of the insides. I would need to see a schematic to say for sure. I doubt that changing the filter caps would solve the problem when and if you find out which ones they are. More than likely the filter caps are the large electrolytic caps I can see. Be sure all your gear is hooked up to the same wall outlet. If not you may have a ground loop problem. You could short out the inputs to see if the noise is internal or from an outside source.

Assuming that's AC power and a fuse holder looped around in that box? can't be good from hum standpoint... Try checking/cleaning input cables and jacks... Can't offer more without a schematic...

Good point!
Is It possible to flip those wires to the outside edge as far from the board as possible.
You could also try a tube shield.

There is a simple way to test to see if it is a ground loop. You can get one of those cheap plugs that convert a 3 prong to 2 prong. That eliminates the ground to the equipment.

If the equipment is on a power bar or conditioner, you can use that 3-2 plug on that, and the equipment rack will be ungrounded. If you try that, and the hum goes away, then you need to figure out which components are contributing to the problem.

I am not recommending that the plug be the ultimate solution to your problem, or that you run your rack long term that way. It is a very cheap, fast way of eliminating ground loops as the source of the hum. Ground loops are very real, and often hard to resolve, even with 'good' equipment.

It might be a very sensible thing to try before you rip into your equipment. If it is a ground loop problem, it will likely still be there when you are done rebuilding your equipment.

What's the hum sound like? Buzz is unlikely filter caps, and hum is only going to be filter caps if it's 120Hz hum. Download on audio oscillator app on your phone.. set it to 60Hz, then set it to 120. Which one sounds more like the hum you're hearing? If it sounds more like 60Hz, you're chasing the wrong problem by wanting to change the filter caps.

I know this is going to be a long answer but everyone of you who tried to help me out deserves it and i am so glad that i am a member of audiokarma.

All of you were right about the problem. they weren't caps, it wasn't even generating inside the amplifier and i discovered it by an accident.

Today i bought the caps from a radio shop and they were cheap. All the caps were just 1.5$. They may not be good brands but they were all matching the amplifier. So i took out the first big caps and replaced them with new (maybe bad brand) caps and connected it to my UPS power supply. * Today i took the whole amp apart, piece by piece.

Guess what happened, Hum is still there. That annoying noise, i used a Lower impedance headphone to check it since it is very audible in those. (Panasonic RP-HTX7). I was sad because i don't want to remove all those tiny caps, i am not an expert in soldering but for some luck the main electricity went off. ( we have bad power in my area ). So the UPS switched to the battery's inverted current. I didn't know that the amplifier was using current from the UPS battery. I off the amplifier desperately and after few seconds switched back on.

VOILA!!!

The hum is gone and it is dead silent. I double checked everything and tube is glowing bright and the hum is gone. Then suddenly the power came back on and the UPS switched to electricity grid and the hum came back. It's with our local electricity. It's not clean enough for sensitive tube amplifier like this. At that moment there was nothing connected to it, just amplifier directly to UPS. but soon as it switched to main grid electricity the hum came back. I tried it several times using UPS battery inverted current and Main grid, for inverted current it is not there.

And i must mention that when i am using the inverted current mode even though the noise is not there, when i switch off the amplifier there is a LOUD POP in the headphones when tubes goes off. It is so loud that i have to take my headphone off second time (Fearing i might damaged my ear). I don't want to plug my sennheiser HD650 to this anymore. I am scared of killing it's drivers. This loud pop sound never comes from main power grid electricity when there is hum. I don't know what causes this but i am sure it has something to do with electricity.

So immediately soldered back the original caps which were Nichicons and kept it at original state now.
 
I had a similar problem with noise on my tube amp, but it varied by time of day (Silicon Valley resident, where LOTS of noise is generated during the day). I got a PowerVar, which has some interesting properties, being an isolating transformer with the resulting neutral being connected to ground. Their web site can provide information, and I have no affiliation aside from using 2 of them. The video showing noise reduction of the various options is particularly impressive and compelling.

Caution. When I fist plugged them in, much of the life went out of the sound. I ended up rewiring them with a high quality power line and plug, and replaced the outlet with a better one. The result was good sound, and no variation by time of day (or at least none that I notice). It could resolve your problem.
 
if there are any computer data centers in your area, go over and ask around. if the power
is that dirty or intermittent, then they will have solutions for each/both.

for you, you have two problems, one fixable with a sine-wave regenerator (the computer
versions are cheaper) or investigate power line filtration, and some form of muting at the
interface between the unit output and the headphones.
 
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