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Hi, I wanna start off by saying that I am new to this forum, so thanks for having me.

So I've had this Traynor YCV40 tube combo amp for 2 years now (bought it used), my first tube amp, and I've had my first issue with it lately. There was a hissing noise, with everything unplugged, coming out of my speaker that would grow louder the more I cranked the volume knob on the amp. When I plugged my guitars in, the hissing would turn into a buzzing, growing louder the more I cranked the pickups volume knob. See the pattern? After some time on the Internet, I figured those where the classic symptoms of a broken tube. My next step was to test my three pre amp tubes to see if any of them was bad, using the Pencile-Tap technique as shown here:
On of them, let's refer it as the middle one, sounded just like in the video (the loud ringing noise). So I bought a EHX 12AX7 tube (the factory ones where Sovtek 12AX7), swapped it with the middle tube, plugged my amp to the outlet, turned it on and...

The hissing and buzzing was still there, loud and clear, guitar plugged in or not (althought it seemed to be less agressive, but I can't be trusted on that). I tried moving the different tubes on different sockets, but nothing seemed to change.

So here are my questions:

Could it be likely that I have had, prior to the replacement, both a pre amp and a power tube broken? Could it be the socket of the pre amp tube at fault here? What should be my next move?

I'm on a tight budget, so it could help me out to consider home repair/testing.
 

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Welcome :)
Perhaps exercise (well) all your shorting input jacks ... including effects loop sockets. Hiss can be finicky to isolate, note differences with lead vs clean channels, note what makes no difference, boost controls, pedals.
Varying hiss with volume says its in front of the whichever volume control you cranked. Can you control it with the tome stack ?

Your hum could be a whole other problem. Figure out if its 60Hz or 120. Probably 60 if it grows when you're cranking up guitar(s) volume controls. Cable, shielding, pickup shield, the room you're in , the circuit you're plugged into , appliances , florescent bulbs. If the hum goes away with guitar vol off... you're getting close to the source.
 

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If your guitar is plugged in, with the guitar volume turned all the way down, do you still get the hiss?

If the gain on the amp is down, with the volume turned up, do you still get the hiss?

Plenty of amps are hissy when nothing is plugged in, so this might be an amp problem as you suspect, or it might be perfectly normal.
 
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