Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Nathan on August 07, 2025, 10:27:28 am
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...and it's not working quite right. This is on a Blues Deville RI.
I used a 5V transformer and bypassed the diode rectifier, tied into the first cap node. Using a 5U4GB.
There is some clear 120 Hz hum coming through which only gets worse as I turn the amp up (and clear harmonics at 240, 360, etc).
So I would love some help in troubleshooting this. Is it my grounding or do I really need to modify my filtering? Add choke? Voltages are all in the right ballpark on my tubes, but the noise is horrid.
Cheers
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See page 14...
https://sluckeyamps.com/misc/Amp_Scrapbook.pdf
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Yup, that's what I did with one exception that I grounded the diodes to a lug with the power cord instead of the first capacitor. That might have caused a ground loop? I am going to try moving that wire over and see if it helps.
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Yup, that's what I did with one exception that I grounded the diodes to a lug with the power cord instead of the first capacitor. That might have caused a ground loop? I am going to try moving that wire over and see if it helps.
A good rule of thumb is that nothing gets grounded with the power cord. You'll see the rule violated all the time, but that doesn't mean you should.
And yes, you could have created a ground loop. I don't think that's what happened in your case as there is it is responsive to volume, but it is possible.
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Well happy camper this morning: I finally moved the ground to first cap and everything is working beautifully! All of my mods worked and the sound is banging. I even like the reverb and drive channel can sound fine. Thanks guys! I have a very usable amp with a good range of bassman to blackface sounds.