5e3 with some low level hum

dankilling

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Check your power transformer bolts. Transformer laminates can vibrate and caus that kind of hum if they aren’t sung, and can come from the factory that way. My 5e3 builds are dead silent except for carbon comp hiss when cranked up.
 

filthytone

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Check your power transformer bolts. Transformer laminates can vibrate and caus that kind of hum if they aren’t sung, and can come from the factory that way. My 5e3 builds are dead silent except for carbon comp hiss when cranked up.
The PT is tight to the chassis. I did tighten the screws on the PT itself earlier, so I don't think it's loose. But maybe I can try tightening as much as I can and see what happens
 

filthytone

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That must be a clue; I can't remember exactly what it suggests, but our brain trust may know. Filters? PT? What else would hum before the tubes warm up?

No one's mentioned PT hum, IIRC. Can you feel the hum if you touch the PT bell housing?

Filters should be 120, but LLC's easy test of gator-ing in an extra filter cap is pretty easy.

This old article by Paul Ruby has some unconventional or inconvenient steps, but it might be worth a read, like your note about the non-buzzy quality of the hum. Scroll down to the What Causes Hum? section.

http://www.paulrubyamps.com/info.html#FirstPowerUp
I couldn't feel anything vibrating on the PT housing. Also, if i disconnect the speaker (just super temporarily), I don't hear any hum or vibrations.
 

dankilling

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You don’t need to crank the PT bolts super hard, but snug is good. If the him goes away with the speaker disconnected, it isn’t mechanical him, it’s electrical. That eliminates another category of hum. Reading through this thread, you’ve eliminated the sources in the preamp, power tubes, and mechanical, correct? At this point, I’d still be leaning towards a grounding issue based on the sound from the video. Is there any change with a guitar plugged in? What about when you touch the strings? As a ‘drop back and punt’ method, you might re flow the solder joints to be sure there isn’t a cold joint in there because those can cause some hard to track issues as well. The 5e3 doesn’t have a lot of joints so it might’ve worth going through the exercise. I also didn’t notice a voltage chart or detailed pics in this thread yet, so those would be helpful as well.
 

filthytone

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You don’t need to crank the PT bolts super hard, but snug is good. If the him goes away with the speaker disconnected, it isn’t mechanical him, it’s electrical. That eliminates another category of hum. Reading through this thread, you’ve eliminated the sources in the preamp, power tubes, and mechanical, correct? At this point, I’d still be leaning towards a grounding issue based on the sound from the video. Is there any change with a guitar plugged in? What about when you touch the strings? As a ‘drop back and punt’ method, you might re flow the solder joints to be sure there isn’t a cold joint in there because those can cause some hard to track issues as well. The 5e3 doesn’t have a lot of joints so it might’ve worth going through the exercise. I also didn’t notice a voltage chart or detailed pics in this thread yet, so those would be helpful as well.
I think I'm going insane. I tested with the speaker disconnected and I do hear a slight hum coming from the PT. Once the tubes warm up, it gets amplified a bit more. I don't feel anything vibrating and everything seems tight.
 

filthytone

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I just used an app to record the audio and it said it's around 120Hz .. so I was VERY wrong about thinking it was 60Hz. Does that also help point at a culprit?
 

Lowerleftcoast

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Hah. You and Uncle Doug had me convinced it was 60Hz. Maybe a solder joint, tube, or transformer.

120Hz and we are back to the ground loops.
 

filthytone

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Hah. You and Uncle Doug had me convinced it was 60Hz. Maybe a solder joint, tube, or transformer.

120Hz and we are back to the ground loops.
I tried the different ground layout from robrob and it didn't change anything, so I don't think it's anything to do with that. The only thing left I can think of to really try is new heaters and location for them and maybe new tubes to test (matched)
 

dan40

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Did we ever verify if the shunt switch on the unused input jacks were closing completely? I know this has popped up in a few builds in the past.

@filthytone ...what is the DC voltage reading from pin 3 of the 6v6 and what DC voltage do you see when measuring across the 250r cathode resistor? Just wanted to see where your 6v6's are idling at.
 

filthytone

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filthytone

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And a few other pics
 

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dankilling

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Thank you- I’m seeing a lot of cold solder joints in there, especially the bus bar on the back of the pots. What wattage iron are you using, and does it have a decently sized tip? Mass allows for quick and hot soldering, which is important working on amps like this. While you don’t want to overheat components, you do want to heat the contact points enough that the solder flows well. You want to see shiny, smooth joints, not jagged dull joints.
 

ElPositivo

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Like @dankilling said, there are a lot of questionable solder joints and then especially on the ground bus on the back of the pots. But I also see cold solder joints on the tube sockets (very clear to see on the heater wires on the output tube sockets for example) and partsboard. I’m afraid you’d have to resolder every connection in the amp. Maybe don’t use lead free solder for this but get some solder with lead as this is easier to solder with. Just don’t inhale the fumes. 😉

The twisting of the heating wiring needs some work, especially close to the pilot light. But you already mentioned you were going to redo this.

It’s tough to see in the pics but is the input of the normal channel shorted via the lead of the 1 meg resistor? From the pics it’s tough to tell if I see a lead over there or not.
 
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filthytone

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@andrewRneumann Yep, tried different 5y3.

@dankilling and @ElPositivo The pot busses look crappy probably because I undid them to try a different ground scheme. Originally they were very clean. However, I'm willing to try all these suggestions, so I'll just go ahead and redo all of the joints everywhere and hopefully I can do a better job with them. I use a Weller 40 watt iron. The solder I used is 60/40 w/ rosin core.

@ElPositivo Yes, the resistor is done the same way on both channels
 

andrewRneumann

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@andrewRneumann Yep, tried different 5y3.

Ok good.

Since you are hearing hum with no speaker and no power tubes, I would focus on your PT and associated wiring. Start with resistance checks on the secondary winding. Measure from red wire to chassis individually. You should see something like 100-200 ohms on each secondary to chassis and they should measure values close to each other. Then measure from secondary to secondary (red to red) and you should see the sum of the earlier resistances you measured to chassis.
Finally measure from the red wires to B+1. You should measure OL—no continuity (unless you installed a bleeder resistor).
Report back.

We are looking for a shortcut that is causing net DC to flow in the secondary which will cause it to saturate and hum. It will also get worse the more DC it pulls (say when the 6V6s are plugged in).

If everything checks out with the resistances, then we need to measure Vac at each red secondary lead wire with the amp operating. We’ll start with the rectifier pulled and then we’ll install the rectifier and see how much it changes. Possibly the resistances check but for some reason one of the secondary wires drops more voltage and doesn’t do any lifting when there is a load on the PT. Then all the current is supplied by one side and we end up with uneven current and DC saturation in the PT again.

Hopefully this makes some sense. I’m not super confident this is the problem, but it’s what makes sense to me given all the symptoms you have reported.
 

King Fan

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I like all the ideas coming in -- don't get frustrated, 'tone. I wasn't kidding when I said there're like 137 causes of hum. You can see this when Andy, who's super smart, says he's not totally confident about the PT -- we just gotta keep checking things off. Someday you'll look back on this and think about what you learned -- trust me, I've done exactly that. Did it again yesterday.

Let's pull over for a sec and look at the map. Does the hum without speaker or tubes sound the same in quality as what you hear when the amp's all hooked up? My ol' boss used to say, "Some dogs have fleas *and* ticks."
 

filthytone

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Thanks all. So this morning I pulled the board out and I'm redoing all the solder joints. I'm also implementing RobRob's layout w/ the ground buss on the board instead of on the pots. The joints are definitely looking shinier (I'll take a pic before I put it all back in so you guys can judge my soldering). Then I'm going to clean all the sockets w/ solder wick and redo all the connections very carefully. Once it's all back in, I'll measure everything again and report back (though hopefully it's all just perfect)
 




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