I recently completed a 36 amp. The thing sounds so awesome except for a persistent hum. The hum is there whether or not a guitar is plugged in. On the TMB channel, it gets a little louder when I fiddle with the volume and it seems to slightly change tone when I mess with the tone knobs. The normal channel doesn't affect it at all.
So maybe, it's possible it's narrowed down to the TMB channel (maybe not?). The hum never really changes volume though, its quite loud and always there.
Does this sound like a grounding issue? Or maybe somethin else? What would be the best way to trouble shoot this? Maybe something with the preamp tube socket?
Aside from the hum, the amp works great and sounds even better, but the hum makes it unacceptable and unusable.
Any help and suggestions are GREATLY appreciated.
Thanks everyone!
-Rich Szmagaj
Help with hum...experts needed
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fzfwyv
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joe6v6
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Im not fimiliar at all with the 36 watt layout but it sounds like a ground issue to me. I have had a very similar sounding problem with a couple 5e3's Ive built and both were cured by moving grounds around. I dont know what layout you used but I would sugest looking at a known good layout and following the grounding schem exactly or as close as you can. Good luck and keep us posted. . Joe
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JonFrum
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If the hum does not get louder when you turn up the volume, then it's probably entering the circuit after the volume pot.
It could be a bad solder joint causing a grounding problem. Components overheated during soldering can be damaged. Try replacing the preamp tubes with known good. If the output tubes are imbalanced, that could cause hum. If you did your own layout, the grounding scheme could be causing a problem.
It could be a bad solder joint causing a grounding problem. Components overheated during soldering can be damaged. Try replacing the preamp tubes with known good. If the output tubes are imbalanced, that could cause hum. If you did your own layout, the grounding scheme could be causing a problem.
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Ballz
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Did you make some DC reference for the heaters? My standard trick involves a 100 (or so) ohm resistor tied from each heater wire to the cathode of one of the power tubes - this usually cures 90% of my hum issues.
2 resistors and 5 minutes of work will tell if it´s a grounding issue or not.
Make sure the heater wires are twisted and running well away (and/or at right angles) from any signal wires.
Also make sure you have the volume and tone controls grounded properly, change their ground points temporarily if in doubt.
I built an 18W some time ago that behaved like this. After much grey hair, I finally moved the tone control ground from the preamp ground to the PI/PWR amp ground point, problem gone.
Cheers /Rick
2 resistors and 5 minutes of work will tell if it´s a grounding issue or not.
Make sure the heater wires are twisted and running well away (and/or at right angles) from any signal wires.
Also make sure you have the volume and tone controls grounded properly, change their ground points temporarily if in doubt.
I built an 18W some time ago that behaved like this. After much grey hair, I finally moved the tone control ground from the preamp ground to the PI/PWR amp ground point, problem gone.
Cheers /Rick
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