Need some help with a problem

[rayma]

So the identical schematic has worked before properly, but not on the new board rev.
Could there be a net list error, maybe a capacitor connected to the wrong point or layer, etc?
Do you have a breadboard version to hack on?

[jwags818]

My new boards will be here in a day or two.
I reduced the 4 layers to 2
Increased clearances
Increased keep out zone around all mounting points
Connected only one sides pour to ground ( I usually connect them all and stitch the hell out of it with vias unless it a dig/analog board then I lay it out carefully and only connect the two grounds in one spot using 0 ohm resistors so we can put caps across them if needed.)
Among the things I tried with the current board:
populated 3 of the 5 I have. All were the same.
At one point I had it lying on top of the chassis with no screws in it and it worked for 4 hours. Sounded great. But then it digressed,
swapped driver tubes back and forth
swapper output tubes back and forth.
bought new coupling caps ( mostly because I wanted to_
Pulled the amp 100% apart and rebuilt in two chassis seperating the power supply.
I am quite sick of working on this thing.

[jwags818]

Here is the NEW board

[rayma]

If both channels of the board are unstable (with different layouts), the D3A could as mentioned
need ferrite bead(s). This is a very wide bandwidth tube. You could cut the traces close to the
tube and add a jumper with the bead, for each tube terminal. I would start with the screen 2,
then the grid, cathode, plate. Do one bead at a time.

Also I would try local bypassing across each filament, 0.1uF.

Last thing to try is adding local decoupling on the board for the power supplies,
a larger electrolytic and a smaller ceramic, for each channel.

[baudouin0]

Also check your tube sockets for corrosion and poor contact. Check inserting valves has not lifted a PCB track. Check for dry joints which may arc and cause static type noise.

[jwags818]

WOO HOO New boards fixed it bigtime...
I have my stereo back ....

breaking in some new Deulend caps. got the cast copper since they were on sale. Also swapped out the resistors on the input to Vishay Precision Z foils.
I have been slumming it with a chinese el84 amp and man what a difference...
Also have a brand new pair of telefunken D3a tubes in it. But not a lick of noise. None...

Thanks to those that attempted to help.

Now I need to finish designing the final chassis for it. going with a couple mono block chassis. Need to buy another power transformers...


Jeff