So I Shorted out the 100k on V1a and both the "SCHHHHH"-noise and the hum gets a lot more quiet but theres still some left, but I think it's a level of hiss/noise that is bearable. I also measuren about 10mA AC on C+ It started at about 7 and raised to 10 as the amp was on for 5 minutes. It seems like it's steady at about 10 now. I also noticed that the power transformer gets quite hot... I can touch it an hold my hand on top of it, but it's not very pleasant.
Edit: I also compared the hum to my signal generator and it sounds like more 50hZ than 100hZ (I'm in Europe so we're on 50hZ, not 60hZ).
Edit3 (phew): The only places I havent messed with anything yet is the cathode bypass cap on V1a and all the resistors up to the volume control. Oh yeah, and the input jack... could that thingy be problematic?
Edit4: Here's a pic of the noise from my scope hooked up to the treble pot "input" (the leg that connects to the 250pf cap. I'm not good at using a scope but You can see theres something funny going on here.
[img2448]https://dl.dropboxusercontent.com/u/43679524/noise.jpg[/img]
Try this simple test with the amp out of its cabinet!
Tape Aluminum foil to a sheet to card board ( both need to be large enough to cover the top of the amp) place it on top of the amp and make sure it grounds to the chassis 100 % some how ( even clip leads are fine ) and yet does not short out to anything, does the noise issue get better?
Also get preamp bypass caps and preamp circuit resistor off of your mind as non of them are the sourse of a hum issue !
If you have another filter that would work at node C then I would unsolder one end of that filter once it discharges and solder a new one across it.
If any filters are going bad and in a partly shorted state then you will have added hum and the added current draw of the small short will run the PT hotter!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
I checked the combo-box and it had indeed aluminum foil in "the ceiling". So I mounted the amp back in and fired it up (I also made sure that the chassis was properly grounded to the aluminum foil. The hum and hiss was not much better, but I noticed some things that stood out a bit betetr when shielded on top. The hum is now constant all the way from 0 to 10 on the volume, maybe a bit too loud still but bearable on louder settings. The hiss/"SCHHHHHHHH"-sound is very mid-heavy and is as good as gone on 0 AND on 10 on the volume. Does that make any sense?
Ooooookay... I am finally closing in on the solution here. After the amp got back in the combo cabinet and got the internal shielding in place thing started to act in ways I could trace errors. It seems like the PCB is picking up excessive amounts of hum no matter what when the amp is opened up without proper shielding. Thank you for pointing in the right direction I had two 7025 tubes at my bench that I pulled from a mid 70s bassman 100. For the heck of it I put them in at V1 and V2. Guess what? That hum is almost gone. When I tried that with the amp open it didnt get much better. I will try to replace the last two tubes as well tomorrow and see if the hum gets even more quiet. I also have a couple of Mullard EL84 tubes that I'll pop in Theres still a certain amount of hiss in the amp, but It's finally playable at lower levels also. So I got new filters and a few other mods done on the way. I think it sounds more aggressive now than before, which is a great thing for me. I think I'm gonna keep it and keep poking around in there to get rid of the hiss as well.
Hiss will always be there in any amp if you have good preamp tubes, what should not be there from preamp tubes is the sound of ocean waves lightly hitting the shore no matter how relaxing that may be after a hard days work, lol!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
2448]https://dl.dropboxusercontent.com/u/43679524/noise.jpg[/img]
I had two 7025 tubes at my bench that I pulled from a mid 70s bassman 100. For the heck of it I put them in at V1 and V2. Guess what? That hum is almost gone. When I tried that with the amp open it didnt get much better. I will try to replace the last two tubes as well tomorrow and see if the hum gets even more quiet. I also have a couple of Mullard EL84 tubes that I'll pop in 