vipor3D wrote: ↑Tue May 09, 2023 3:17 pm
Well I got the parts ordered. Hopefully they'll come soon. In the meantime I guess I'll look over everything and verify the heater wiring is correct
The fact that "the guitar signal came through as expected and sounded pretty good" indicates that the filaments are wired correctly.
However, since you have time, it would be worthwhile to go back through the excellent installation instructions step by step to verify that everything is connected properly. If you had done this before you turned the power on, we probably would not be having this conversation.
vipor3D wrote: ↑Tue May 09, 2023 2:39 amThe only thing that I seemed to notice wrong was a loud hum. The guitar signal came through as expected and sounded pretty good except for the hum. Any suggestions on where to start to eliminate it?
Another clue is the hum frequency. Is it line frequency (50 or 60Hz) or double that (100 or 120Hz)? Line frequency means the source is un-rectified AC, i.e. heater wiring. Make sure he heater string has a ground reference. I don't see a grounded center tap or other ground reference (100 ohm resistor from each side of the heater string to ground) in the kit instructions or in your photo. I would connect a 100 ohm resistor from each lug on the pilot lamp to the ground lug on the terminal strips holding the filter caps.
Double line frequency means the source is rectified DC, which usually means the ripple voltage just after the rectifier is getting into the signal path.
I'm pretty sure it's 60Hz hum. Not sure if it will help, but I took a quick video of the sound:
The hum does remind me of the hum I got the time I had a grounding issue with my guitar pickups. Could it be an issue with something in the stock setup not being grounded as it should per the instructions? I've seen multiple builds of this amp that followed the instructions exactly and they didn't have the loud hum that I do. The chassis is painted and the instructions mentioned filing the chassis holes down to get through the paint layer. I did this, but I'm wondering if I may have not done it well enough. Could that possibly be related to the hum?
vipor3D wrote: ↑Tue May 09, 2023 3:17 pm
Well I got the parts ordered. Hopefully they'll come soon. In the meantime I guess I'll look over everything and verify the heater wiring is correct
The fact that "the guitar signal came through as expected and sounded pretty good" indicates that the filaments are wired correctly.
However, since you have time, it would be worthwhile to go back through the excellent installation instructions step by step to verify that everything is connected properly. If you had done this before you turned the power on, we probably would not be having this conversation.
Lol I know I should've been more patient and take the time to thoroughly review everything, but my excitement got the better of me. Live and learn I guess
vipor3D wrote: ↑Tue May 09, 2023 2:39 amThe only thing that I seemed to notice wrong was a loud hum. The guitar signal came through as expected and sounded pretty good except for the hum. Any suggestions on where to start to eliminate it?
Another clue is the hum frequency. Is it line frequency (50 or 60Hz) or double that (100 or 120Hz)? Line frequency means the source is un-rectified AC, i.e. heater wiring. Make sure he heater string has a ground reference. I don't see a grounded center tap or other ground reference (100 ohm resistor from each side of the heater string to ground) in the kit instructions or in your photo. I would connect a 100 ohm resistor from each lug on the pilot lamp to the ground lug on the terminal strips holding the filter caps.
Double line frequency means the source is rectified DC, which usually means the ripple voltage just after the rectifier is getting into the signal path.
I'm pretty sure it's 60Hz hum. Not sure if it will help, but I took a quick video of the sound:
The hum does remind me of the hum I got the time I had a grounding issue with my guitar pickups. Could it be an issue with something in the stock setup not being grounded as it should per the instructions? I've seen multiple builds of this amp that followed the instructions exactly and they didn't have the loud hum that I do. The chassis is painted and the instructions mentioned filing the chassis holes down to get through the paint layer. I did this, but I'm wondering if I may have not done it well enough. Could that possibly be related to the hum?
I should note, the output is going through an attenuator, so it's not as loud as it would be straight to the speaker.
vipor3D wrote: ↑Tue May 09, 2023 2:39 am
Update - I reviewed everything again realized both red PT wires were one lug off instead just the one initially noticed here. I made the change and tried the amp again and it came to life!
The only thing that I seemed to notice wrong was a loud hum. The guitar signal came through as expected and sounded pretty good except for the hum. Any suggestions on where to start to eliminate it?
See attached pic...
UPDATE: I replaced the large filter cap and the one diode, I also found a wire on the treble pot that hadn't been soldered and fixed that. I was really hoping all of those things would resolve the hum issue I'm having but unfortunately I still have it.
It doesn't seem to be affected by the treble or bass controls, and the volume increases it. It also seems that turning up the guitar signal changes the hum to more of a buzz.
I took another video demonstrating this. The video starts with the guitar volume on 0 and me going through the amp controls. Not sure if the video captured it well, but the hum reduces a bit after about 75% volume. After I go through the bass and treble, I turn up the guitar signal and you can hear the hum turn into more of a buzz. You may have to turn up your volume, youtube seems to suck a lot of the volume out of the original video.
Any ideas on where I should go from here? My thoughts were to unscrew some of the hardware that's supposed to ground to the chassis and scrape the entire contact point bare of any paint and ensure the grounding connections are good. After that, I'm not really sure what else to try
If your heater supply has no connection to ground, try connecting 100 ohm resistors from each of the pilots lamp lugs to the ground lug on the nearby terminal strip. You could do a quick test with one resistor clipped in to see if it makes any difference.
Between last night and this morning I've replaced all 3 filter caps, I replaced both rectifier diodes, I unscrewed the grounding points and filed all the paint away on the chassis, and I tried resoldering all the pots since I'm noticing issue with the volume pot and the hum/buzz but none of that fixed it.
The only things I have left to try today is swapping the 12ax7 to see if it's an issue with the tube. I'm also going to order a new volume pot to see if it could possibly be a bad pot.
I really want to figure out the issue with the amp as it is based on the instructions, because I've seen multiple builds that followed the instructions exactly and don't have the hum that I do. If I can't solve it as is, then I guess it's onto mods that might can address the issue.
Stevem wrote: ↑Sat May 13, 2023 3:10 pm
Don’t waste money on a new pot as that’s not that can’t be the source of your hum.
The new volume pot is more of a hail mary based on the symptoms. I came across some posts online last night that had similar issues to what I'm experiencing and a new pot fixed the issue.
The main reason I was considering that was the way the hum/buzz interacts with the volume pot. It buzzes up to about 65%, then gets scratchy, then at about 80% the buzz stops and remains stopped as the volume is between 80-100%
An earlier version of the schematic shows two 100 Ohm resistors on the pilot light holder, but on this version, one side of the heater supply is connected to the cathode of the EL84. If you have added any resistors per suggestions above, remove them, they will alter the bias of the EL84.
I think a "Chop stick" test is in order. You move wires around with an insulated stick and try to find one or more wires that are sensitive to movement in regards to hum. Can you post a picture of the wiring around the tube sockets. Be very careful, you have to do this test with the power on and speaker connected.
LOUDthud wrote: ↑Sat May 13, 2023 7:34 pm
An earlier version of the schematic shows two 100 Ohm resistors on the pilot light holder, but on this version, one side of the heater supply is connected to the cathode of the EL84.
The cathode elevated heater string is shown in the schematic and layout, but does not appear to be in the posted photo of this build.
You do not have the required permissions to view the files attached to this post.
LOUDthud wrote: ↑Sat May 13, 2023 7:34 pm
An earlier version of the schematic shows two 100 Ohm resistors on the pilot light holder, but on this version, one side of the heater supply is connected to the cathode of the EL84. If you have added any resistors per suggestions above, remove them, they will alter the bias of the EL84.
I think a "Chop stick" test is in order. You move wires around with an insulated stick and try to find one or more wires that are sensitive to movement in regards to hum. Can you post a picture of the wiring around the tube sockets. Be very careful, you have to do this test with the power on and speaker connected.
I've been working on it the past couple of hours - I filed down the paint under the input and output jackets, resoldered any joints that looked questionable, swapped out the 12AX7 and even redid the filament wiring from the pilot light to V2. None of that changed anything, so I guess it will be onto the chopstick test. I'll open the amp back up shortly and take a picture of the tube socket wiring. Had to step away for a bit before I go crazy
Last edited by vipor3D on Sat May 13, 2023 11:04 pm, edited 1 time in total.
LOUDthud wrote: ↑Sat May 13, 2023 7:34 pm
An earlier version of the schematic shows two 100 Ohm resistors on the pilot light holder, but on this version, one side of the heater supply is connected to the cathode of the EL84.
The cathode elevated heater string is shown in the schematic and layout, but does not appear to be in the posted photo of this build.
I apologize but I'm not sure exactly what you're referring to with the cathode elevated heater string. I've been rechecking the instructions/layout and I'm not seeing anything missing. Are you referring to the connection between pins 3 & 4? It's hard to see in that initial photo I posted, but the connection is there. I'll post a new picture shortly since I redid the filament wiring from the pilot light to V2
martin manning wrote: ↑Sat May 13, 2023 11:41 pm
Yes, that's it. The heater circuit (at pin 3) is tied to the output tube's cathode (pin 4) to give it a DC reference voltage.
Here's an updated picture of the tube socket wiring. It's somewhat hard to see, but the twisted wire from the pilot light is going under the wires at pin 5 of V2 to connect to pin 4
You do not have the required permissions to view the files attached to this post.
