18 watt clone build Hum question

[jamme61]

Just built this marshall 18 watt clone https://d1sjrnpi226dnf.cloudfront.net/s ... 1382030168

in the instructions it said to ground the input jacks with this special washer that mounts on the cliff jacks. I noticed i have a Hum that gets pretty loud as I turn up the volume. Does this sound like a ground loop problem and could it be those cliff jacks being grounded? I attached a picture of the build to see any other problems Thanks for any help this my first build so Im just learning this stuff.

one more thing its hard to see that the cliff jacks are grounded - I didn't have the special washer so I used the buss wire instead of the washer.

[The Ballzz]

Looks pretty good, especially for a first build. First suspect on my list would be lead dress, particularly surrounding the heater wiring. Use a chopstick to lift, jostle and move wires around with amp humming to see if you can find which wire or wires makes the hum worse or better. Other than that, more experienced builders will likely speak up soon!
HTH,
Gene

[Mark]

You need to give more info. Is the hum present in both channels?

The Cliff jacks don't provide an earth so the earth contact is essential.

[jamme61]

Ok so the cliff jacks do need to be grounded where they meet the chassis ? I did it the way the instructions say but on other Marshall's I have had, they have never been grounded there? Any way more info is that the hum is really low and not a problem until the volume is maybe at half - really loud
It hums in both channels and maybe it's supposed to hum this loud at volume? I will check with the chopstick- move some wires also maybe try different tubes? I was just so excited that this worked when I first tuned it on that I checked the voltages and couldn't wait to mount it back in the combo to play it. Thanks for the time on this any other suggestions or tips are welcome.

[martin manning]

I don't see the need for the grounding washer if the sleeve lugs on all of the jacks are grounded at the lug under the stand-off. In fact it creates a small ground loop.

Is the hum noticed with or without a guitar plugged in?

[Phil_S]

An amp isn't supposed to hum. It should be so quiet you can hear a mouse relieve itself. Sometimes we tolerate a little bit of hiss or hum because it becomes too much trouble to fix it, or because we've identified the source and chosen to ignore it, but it shouldn't be there.

As already said, you don't need that special washer and I can't understand why it's there. Grounding the sleeve connection to the buss is all you need. FWIW, I agree with Martin that using the washer creates a ground loop.

What makes you think the input jack is the source of the hum? I am thinking no real diagnostic procedure has been done and you are just focusing on the missing part that isn't needed and shouldn't be used even if you have it.

If it hums, the first thing I'd want to know is whether it is 60Hz or 120Hz. Once we know that, we can start to look for the trouble. It is possible you have both and that one masks the other, but this is not typical for a hum problem. 55Hz is the fundamental for A. So 60Hz is between A and Bb. 120Hz is roughly the first fret on the A string. To get 60Hz you need to tune down the E string about 4.5 "frets-worth." On the piano 60Hz is between keys 14 and 15; 120Hz is between keys 26 and 27. (You didn't post location. If you are in a 50Hz location, adjust accordingly for 50/100Hz.)

I suggest we start at the beginning and determine the frequency of the hum. 60Hz tells us it is coming from a AC voltage source (usually heaters). 120Hz covers pretty much everything else, including ground loops.

[jamme61]

An amp isn't supposed to hum. It should be so quiet you can hear a mouse relieve itself. Sometimes we tolerate a little bit of hiss or hum because it becomes too much trouble to fix it, or because we've identified the source and chosen to ignore it, but it shouldn't be there.

As already said, you don't need that special washer and I can't understand why it's there. Grounding the sleeve connection to the buss is all you need. FWIW, I agree with Martin that using the washer creates a ground loop.

What makes you think the input jack is the source of the hum? I am thinking no real diagnostic procedure has been done and you are just focusing on the missing part that isn't needed and shouldn't be used even if you have it.

If it hums, the first thing I'd want to know is whether it is 60Hz or 120Hz. Once we know that, we can start to look for the trouble. It is possible you have both and that one masks the other, but this is not typical for a hum problem. 55Hz is the fundamental for A. So 60Hz is between A and Bb. 120Hz is roughly the first fret on the A string. To get 60Hz you need to tune down the E string about 4.5 "frets-worth." On the piano 60Hz is between keys 14 and 15; 120Hz is between keys 26 and 27. (You didn't post location. If you are in a 50Hz location, adjust accordingly for 50/100Hz.)

I suggest we start at the beginning and determine the frequency of the hum. 60Hz tells us it is coming from a AC voltage source (usually heaters). 120Hz covers pretty much everything else, including ground loops.

Its 60hz and it gets louder when I increase the volume. I did ground the inputs as per the instructions but wondered about it because, of my older marshalls not being grounded like that. I'm about to take the amp out of the combo to disconnect those grounds - chopstick- check the preamp tubes. Thanks again for the time and help I'll report back asap

[Richie]

I think like some suggest, i'd first try to narrow it down to what section the hum is coming from. V2 in this layout is the PI. So if you remove V1 and V3 you still hear the hum? if so, then its going to be in the PI or power section.

And also tubes are the first thing to change, so you make sure your not tearing an amp completely apart, only to find it was a noisey hummy tube!
And some can be pretty bad and cause these problems. Even brand new ones.

And as mentioned, moving some wires to see if it effects things. 18 watters can be a tricky amp. Sometimes twisting the plate wires to the PI help. Sometimes not, and they need to be separated. And those wires run or pushed back under the board as much as possible. Also as was mentioned are the grounds. You might try moving the CT (center tap) to a different spot like the ground for the AC. See if it makes a difference.
I know it may sound funny, but it does and can have an effect sometimes. And that can be with all the grounds.
The best thing to do is look at some pics of maybe the handwired marshall,or pics of old 18 watters, and use ground hookups where they did. Also look at the wiring layout.

[jamme61]

I think like some suggest, i'd first try to narrow it down to what section the hum is coming from. V2 in this layout is the PI. So if you remove V1 and V3 you still hear the hum? if so, then its going to be in the PI or power section.

And also tubes are the first thing to change, so you make sure your not tearing an amp completely apart, only to find it was a noisey hummy tube!
And some can be pretty bad and cause these problems. Even brand new ones.

And as mentioned, moving some wires to see if it effects things. 18 watters can be a tricky amp. Sometimes twisting the plate wires to the PI help. Sometimes not, and they need to be separated. And those wires run or pushed back under the board as much as possible. Also as was mentioned are the grounds. You might try moving the CT (center tap) to a different spot like the ground for the AC. See if it makes a difference.
I know it may sound funny, but it does and can have an effect sometimes. And that can be with all the grounds.
The best thing to do is look at some pics of maybe the handwired marshall,or pics of old 18 watters, and use ground hookups where they did. Also look at the wiring layout.

Thanks I will take a look at the old 18 watters - great idea. I removed the extra grounds on the input jacks, hum was gone in the trem channel and maybe 90% gone in the normal channel. So I figured maybe a bad tube if its only one channel? After checking the tubes and still having some hum (only in normal channel) at 3/4 volume I'm pretty happy and thinking of moving on and enjoying the amp. I have messed with the wires and tubes and still a little hum on the one channel? even replaced the Cathode Cap on V1 which wasn't soldered in on the + side -(see picture) if anyone see's something else to try let me know, otherwise i'm closing it up and playing. it sounds really good IMHO Thanks to all you guys for taking the time to help - really appreciate it

[Richie]

[jamme61]

OMG take a look at the 22uf filter cap on the board- I never grounded it. Now this amp is as quiet as a mouse pissing in to a cotton ball LOL. Hey Im a rookie,
stupid mistake- very happy- thanks again if anyone's still out there.

[Mark]

Good to hear you've solved the problem. The other thing to consider is the screen grid resistors. The 1K valves offers the output tubes real protection but there will be less bass response as a result of the 1K resistors.

[jamme61]

Good to hear you've solved the problem. The other thing to consider is the screen grid resistors. The 1K valves offers the output tubes real protection but there will be less bass response as a result of the 1K resistors.

Thanks what are other values to try? I think I saw 100 ohm here. Thanks