Request for Help Troubleshooting 5E3 Noise Issue?

[Dumbmonkey]

Hi everyone!
I have a 5E3 build that I completed using the Optimized 5E3 layout information that Rob Robinette posted on his pages:
https://robrobinette.com/5e3_Modifications.htm#Optimized_5E3_Layout
It is pretty much stock, except that I'm running a 12AX7A in V1 and I split the cathodes on V1 to implement Rob's Lead Channel mod:
https://robrobinette.com/5e3_Modifications.htm#Lead_Channel
I also changed the phase inverter caps from .1uf to .022.
Here's the issue; with the volumes and tone all the way down, there is a static sounding noise that I can only describe as grinding, static, and slight motorboating.  I tried pulling both preamp tubes to see if it might be a preamp issue and it persists.  I also tried moving lead wires with chopstick but didn't seem to get any difference.  I thought it might have something to do with the power tubes (NOS Soviet 6V6), so I tried some JJ's from my Deluxe Reverb.  That helps a little, but the noise is still there.
I thought it might be a grounding issue but I can't find any issues with the multimeter, I'm getting continuity at grounding points.
Any thoughts as to where I should start looking?  Other than the background noise, the amp works and sounds just fine (actually, its sounds pretty great!)
Thanks in advance!

[AlNewman]

Could you post pictures?

[Latole]

Good pictures are a must

Did you have schematic as build ?

[Dumbmonkey]

Hi and thanks for looking!
I’m going to try to post pics, but I have to fix the file sizes to attach them.
Here’s a full view of the chassis.

[shooter]

the 2nd link shows a Weber layout with voltages, how close to those are you?


Got a scope?


couldn't find a schematic on that page, I'll look again.

[Dumbmonkey]

Hi,
My voltages are higher than the posted Weber voltages, but I think that's because the Hammond Power Transformer (T290BBX) I'm using puts out more voltage than the traditional 5E3 transformer.  After I completed the build, I read that other users recommend the T290BX for the 5E3 to keep the voltage more "vintage".
Anyway, here are the voltages I have from the last time I measured them.
B+1 387
B+2 345
B+3 270

V1 12AX7A
#1 147
#3 1.47
#6 174
#8 1.4

V2 12AX7A
#1 184
#3 1.39
#6 219
#7 15.5
#8 50

V3 & V4 6V6GT
#3 379
#4 343
#8 21

[Dumbmonkey]

I'm going to try to post some more pics.
Here is a closer look at the preamp and power amp sections of the board.

[shooter]

armchair math says you're dissipating about 15W a tube


21/250 = 84mA /2(tubes) = 42mA/tube * ~~ 360 plate vdc = ~~ 15W


might be enough to push them into a parasitic oscillation.


Can your multimeter handle 600vdc max when reading VDC or VAC?

[Dumbmonkey]

Hi again,
Sorry I didn't reply sooner. 
The plate dissipation is definitely an issue, and on the advice of some others on the forum, I increased the first dropping resistor (4.7K) to lower the screen voltages.  I settled on a 22k which seems to get my dissipation down to 12.51 on the inner tube and 13.27 on the outer, which I think is in spec for 6v6s.  I went back to re measure my voltages, and was getting some loud buzzing noises on V2 #3 whenever I put the probe there.  It's supposed to be around 1.2 volts, but  the noise made me nervous that something else was amiss.
I've decided to pull the board, check underneath for solder blobs and bridges, recheck and reflow all my connections and fire it back up as a new build. 
I'll post back afterward if anyone is curious.
Thanks for all your help!  It's truly appreciated!
cc

[Dumbmonkey]

Hi again!
It's been a while, but I wanted to provide a bit of an update with another question.  I finally got around to pulling out the circuit board and checked underneath.  There were some pretty big solder blobs under there that I took care of and cleaned some joints up underneath.  When I got everything back together, the amp was much quieter, although there was still a bit of noise and some random popping.  I checked all the stuff that's supposed to be grounded with a multimeter and it looks good.  I chopsticked throughout the amp and I did notice that the wire that connects the pots to pin 2 of V2 was microphonic when I tapped on it.  Is it supposed to do that? It doesn't seem right to me.  I replaced that wire with some shielded, which helped somewhat but it's still microphonic.  What is everyone else's experience with this sort of thing?
Thanks again!

[ac427v]

I created that symptom once by getting solder/rosin spatter inside a pot. It was very hard to troubleshoot    I eventually found it by using the chopstick to push on the pot terminals. A new pot fixed it. Good luck!

[Dumbmonkey]

That's interesting to know!
I was thinking of replacing the pots with CTS at some point to see if that did anything as one of the volumes is a bit spotty at the beginning of the taper. 

[Willabe]

I created that symptom once by getting solder/rosin spatter inside a pot. It was very hard to troubleshoot    

That's happened here several times.

When I solder up a pot that has an opening in the shield cover, so you can clean it, I put a small piece of blue painters tape over the opening. It stops any splatter from getting in.

[Joel]

I've had this happen.  Usually it's a bad solder joint at one end of the wire - or sometimes if it's a tube socket, a dodgy socket to tube pin connection.  One time I had a similar fault to this and it was the wire itself, only one of the copper strands touching across an internal open circuit. 

Hi again!
It's been a while, but I wanted to provide a bit of an update with another question.  I finally got around to pulling out the circuit board and checked underneath.  There were some pretty big solder blobs under there that I took care of and cleaned some joints up underneath.  When I got everything back together, the amp was much quieter, although there was still a bit of noise and some random popping.  I checked all the stuff that's supposed to be grounded with a multimeter and it looks good.  I chopsticked throughout the amp and I did notice that the wire that connects the pots to pin 2 of V2 was microphonic when I tapped on it.  Is it supposed to do that? It doesn't seem right to me.  I replaced that wire with some shielded, which helped somewhat but it's still microphonic.  What is everyone else's experience with this sort of thing?
Thanks again!