120hz hum in new build

[bepone]

follow by oscilloscope where buzz starting with input jack normally grounded and report here, after anode capacitor , scope AC coupling.
(did you make ground on input jack switch contact to gnd when is no jack in- this can cause loud humm?)

[bepone]

Where would you suggest grounding B+1/B+2 nodes then? I've tried grounding that cap can node off the main buss onto another spot in the chassis and it didn't make and change.

B1 and B2 for preamp stages must be connected to PI supply capacitor gnd because current goes from there, follow the stream of current from schematic..Pi supply capacitor should be connected to g2 supply cap.. g2 then to anode supply cap.. follow one logic stream, from low current in input jack to high currents in output tubes supply.

channel 1 and channel 2 gnd , both to the input jack.

heaters gnd to clean gnd part - input jack gnd.

there should be no any other connection from DC gnd to chassis, only at the input jack.

capacitor gnds shuold be connected by wire from one to the other gnd terminal, chassis should be treated like it is not conductive at all *read like it is from plastic, and not used for gnd return paths

[beasleybodyshop]

follow by oscilloscope where buzz starting with input jack normally grounded and report here, after anode capacitor , scope AC coupling.
(did you make ground on input jack switch contact to gnd when is no jack in- this can cause loud humm?)

So i tried to do this, but my scope is not doing a great job of actually seeing the noise present.

I know the noise happens in the first stage, because if I short to ground the grid input the noise does not change; If I short to ground the plate connection of the first stage with a .1uF film cap connected to clip leads the noise goes away.


And, another mystery solved - I reflowed the center tap on my heater winding and the amount of "hum" has dropped to nearly imperceptible levels. At this point, the only noise of note is the loud buzzing sound that occurs when the master volume is turned up and the channel gain control is turned up. Again, the noise goes away if I short before OR after the first stage coupling cap.

[WhopperPlate]

follow by oscilloscope where buzz starting with input jack normally grounded and report here, after anode capacitor , scope AC coupling.
(did you make ground on input jack switch contact to gnd when is no jack in- this can cause loud humm?)

And, another mystery solved - I reflowed the center tap on my heater winding and the amount of "hum" has dropped to nearly imperceptible levels.

And this is why I consistently repeat the mantra : solder is not glue.

Solid mechanical connections make even the worst soldering potentially functional

[beasleybodyshop]

follow by oscilloscope where buzz starting with input jack normally grounded and report here, after anode capacitor , scope AC coupling.
(did you make ground on input jack switch contact to gnd when is no jack in- this can cause loud humm?)

And, another mystery solved - I reflowed the center tap on my heater winding and the amount of "hum" has dropped to nearly imperceptible levels.

And this is why I consistently repeat the mantra : solder is not glue.

Solid mechanical connections make even the worst soldering potentially functional

To be fair, this solder point was wrapped around a physical termination before soldered. Perhaps the flux in the solder didn't clean the surface enough to stick well. Then again, I could have prepped the termination better so I'll gladly take the criticism

[WhopperPlate]

And, another mystery solved - I reflowed the center tap on my heater winding and the amount of "hum" has dropped to nearly imperceptible levels.

And this is why I consistently repeat the mantra : solder is not glue.

Solid mechanical connections make even the worst soldering potentially functional

To be fair, this solder point was wrapped around a physical termination before soldered. Perhaps the flux in the solder didn't clean the surface enough to stick well. Then again, I could have prepped the termination better so I'll gladly take the criticism

I hear you, been there . A quick wipe with steel wool or some solvent on the leads of components is my favorite preliminary treatment to generally prevent this issue . Even those fresh sealed packs of components from the distribution can have enough residue to contaminate and prevent a good solder joint .

[bepone]

so it was heater filament...

now if is necessary it is possible to play with the grounding.. but basic buss gnd should do the job..

[bepone]

many new terminal tags and strips(NOS even worst) can have bad solder acceptability, sockets too, should be brushed to remove top metal oxide..

[rangdipkin]

Dirty ol' center tap! You might be able to get a further reduction in hum by tying your heater CT to your power tube cathodes for some heater elevation, go easier on the cathode follower section as well. As long as you are fully bypassed it should be a nice clean elevation voltage.

[GAStan]

I hear you, been there . A quick wipe with steel wool or some solvent on the leads of components is my favorite preliminary treatment to generally prevent this issue . Even those fresh sealed packs of components from the distribution can have enough residue to contaminate and prevent a good solder joint .

Charlie while I'm in awe of your vast experience and excellent help you provide here on TAG I must respectfully disagree with having steel wool anywhere near my workbench. A stray strand stuck to some Flux residue could lead to a very exciting power-up. Also anything magnetic will attract it.

When I learned to solder (mil-spec) we were taught to use pencil erasers, the good old fashioned pink rubber type. The large ones work well for loose components and the ones on a pencil can reach places too small to get a finger to. They are slightly abrasive and do a great job of preparing a surface for solder.

[WhopperPlate]

I hear you, been there . A quick wipe with steel wool or some solvent on the leads of components is my favorite preliminary treatment to generally prevent this issue . Even those fresh sealed packs of components from the distribution can have enough residue to contaminate and prevent a good solder joint .

Charlie while I'm in awe of your vast experience and excellent help you provide here on TAG I must respectfully disagree with having steel wool anywhere near my workbench. A stray strand stuck to some Flux residue could lead to a very exciting power-up. Also anything magnetic will attract it.

When I learned to solder (mil-spec) we were taught to use pencil erasers, the good old fashioned pink rubber type. The large ones work well for loose components and the ones on a pencil can reach places too small to get a finger to. They are slightly abrasive and do a great job of preparing a surface for solder.

You must mean my VAST INEXPERIENCE!

No sparks yet!

Lol , all kidding aside , this is no joke , I blast the hell out of each amp with an air compressor before I turn them on again. Even worse than a stray steel strand is a clipped lead that managed to fly under the board! You can never be too careful.

To emphasize your point, I keep the steel wool far away from the work bench in its own zone, near all the other metal work . I dare not bring that devilish concentration of magnetic disaster anywhere near the actual amp

But you are right , pencil eraser is far less messy and meets mil spec ! Works great especially inside the amp! But oh look how fast that NOS corrosion disappears with a swipe of the wool ! Lol oh the blasphemy

[sluckey]

I keep a #0000 steel wool pad and 600 grit sandpaper beside my PACE workstation. Served me well for over 40 years. Great for shining up those old CC leads. Rarely need it since switching to metal film.

[beasleybodyshop]

Dirty ol' center tap! You might be able to get a further reduction in hum by tying your heater CT to your power tube cathodes for some heater elevation, go easier on the cathode follower section as well. As long as you are fully bypassed it should be a nice clean elevation voltage.

This is my next step, thanks for jogging my memory!

I think the improper choke/standby wiring was masking a lot of the other changes I attempted to make during the first 12 hours of pulling my hair out on this issue

[beasleybodyshop]

Done and dusted boys and girls! I added clip leads to the various filter caps and just moved them around until i got the lowest noise floor. The amp is reasonably quiet now and sounds fantastic! Moral of the story is reflow all your solder joints and elevate your heaters

[WhopperPlate]

Done and dusted boys and girls! I added clip leads to the various filter caps and just moved them around until i got the lowest noise floor. The amp is reasonably quiet now and sounds fantastic! Moral of the story is reflow all your solder joints and elevate your heaters

What ground scheme ended up the quietest for you?