Help with 120Hz hum issue on Bogner Clone

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versital

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I Built 2 Bogner uberschall clone amps and they both suffer from a 120hz hum. Amp sounds great minus a loud 120HZ Hum I can’t get rid of. The Hum can be heard with all volume pots off and gets louder as you raise the volume. I’ve been trouble shooting with one and I have done the following things trying to fix it.
Upgraded and replace Filter caps
Upgraded and replace Choke
Replaced Preamp Tubes & Power tubes
Re-positioned OT orientation
Upgraded and replaced Bias rectifier, filter caps
Upgraded and replaced DC heater circuit for preamp tubes
Removed ground loops with FX loop and Footswitch jack
Revised Grounding paths
Upgraded Switching relays
Retraced all solder and wire connections points

I assume its related to the B+ power supply after rectification and can be heard with volume off but not in standby. It appears once Amp is warmed up.
I as a last effort I started replacing all the 180k and 100k ½ watt metal film resistors feeding from B+ and replaced with 2w Metal Oxide Resistors. The result was it lowered the Hum by 25% in general and 80% on the clean channel.

Does Anyone have any other ideas what will cause a 120hz hum??????.
 
Try moving the amp to a completely different location. Different building with good mains wiring if possible. It could be from outside interference or the power in your wall, for one.

But, if it's 120 cycle hum then it's probably from inside your amp, after the power section. If it were 60 cycle, then I'd suspect grounding/mains power. Maybe. I'm not an expert.

I was dealing with noise issues as well but I realized it was because the room I'm in is close to a telephone pole outside on the street that has a large transformer on it. Once I moved the amp to the other side of the building, away from the power line, noise went down considerably.
 
120Hz is full wave rectified AC. Check lead dress with regards to B+ supply to filter caps. If that does not turn up anything, more than likely it has to do with poor grounding within the amplifier.

Trace all grids and see if you have one running near a filter capacitor or unrectified AC.
 
Did you scope it to verify it's 120hz? 60 and 120 sound very similar.
 
Its definitely a 120Hz as it is a full octave higher than 60Hz hum you get when you open the guitar pot. I have taken it to a repair shop and they tried to isolate it also but was unsuccessful but did find other problems we corrected. So it is not the power in my house. I also built a PTP Turret version of the amp a few years ago and it also had same issue so I'm beginning to think it is the Overdrive circuit and I've compared 3 schematics found on the Bogner Uberschall and they all have almost the same component values.

The Bogner Ubershcall has almost the same schematic layout as a Soldano SLO with just a few gain mods. The PCB layout is quite different but It's just moved around with a few extra caps and resistors that can be easily bypassed or removed. I decided i will revert/mod it to all SLO clone values on the overdrive channel and that may just fix the issue and sound better with more gain control. The Uberclone has almost the same gain but just maxed out in the gain stage making the gain control nob almost useless.
 
try a star grounding lay out. uf diodes on the bridge pack
 
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