5E3 noise cured - but what was the cause?

jhundt · September 26th, 2004, 12:14 PM

I have an old Deluxe 5E3 - not one of those beautiful replicas. but an old war-horse from the 50's. Many components have been replaced, including most bypass, signal and filter caps. Lately I was getting lots of noise of the snap-crackle-pop variety. It was pretty steady while the amp was being used, only sometimes it would mysteriously stop for a while.

I opened the thing up and hunted around for bad connections, components, etc. Couldn't find anything obvious, and the darn thing wouldn't make the noises when I was working on it. Tried different tubes, cables, guitars. That didn't solve the problem.

Then I touched the back panel and the noise stopped. Took my hand off the panel and it started again. Touched the panel again, and the noise stopped.

When I got this amp, the interior surface of the back panel had remnants of something that looked like asbestos on it. I decided to cover that stuff up with aluminum adhesive tape, which would also help to shield the unshielded side of the chassis.

Now it seems that the tape on the panel is not making good contact with the chassis, and somehow this is causing the snap-crackle-pop noise. If I remove the back panel completely the noise goes away, so it's not just stray interference. (In fact, there is a barely audible increase in background noise when I remove the panel, but none of the problem noises).

Well now I know what the problem is, and how to fix it. But can anyone explain the science to me? If the chassis is grounded, why should the quality of the back-panel contact create noise?

fontaine · September 26th, 2004, 03:48 PM

The science part i have no clue but i do know that my
"54" Deluxe has an asbestos shield also, obviously to
provide a heat shield. As far as stickin something metal
based where it was not designed to be i think i would
not do that. I don't see how it would help anything from
a performance standpoint and quite possibly would just
act as some sort of RF antennae.But like i said i am no
expert and i'm sure somebody here could noodle out
the real problem for you.
Don't you just groove on the old tweedies? I know i
sure do.I can even stand the odd snap or crackle.It
just adds to the thrill.Kinda like the same reason i drive
an Alfa Romeo.These things have their own personalities!

jhundt · September 27th, 2004, 01:23 AM

I love my old amp, and my friends laugh at me because this amp and my others (including home-made stuff) are all prone to buzzes and hums. But I don't mind, mostly.

I am attracted by those nice new 5E3 replica kits, especially with a 15" speaker. But I can't afford one. My Fender only cost $50.

As far as putting that aluminum tape there on the back panel, I noticed that when Fender changed his amps to a top mount design he put a shielding plate against the open side of the chassis, so I thought I'd try it too. Until this noise started I've never had a problem.

fontaine · September 27th, 2004, 12:29 PM

I would love to hear one of these thru a nice 15" Jensen.
I believe Lance has one up and running and likes it alot.
The one thing i have done is to replace the original spkr.
with a p12n Jensen reissue and that was like adding a
turbo.Good luck in the never ending tone quest!

Lance · September 27th, 2004, 05:53 PM

Yeah - the 15" rocks! I'm using this as my band amp now and it just sounds amazing.

jhundt · September 28th, 2004, 02:12 AM

I built my home-made "BuzzBomb" (copy of a Vox AC-c0 TB but with only 2 EL-84's) into a combo with an old JBL K-130 (?) in a closed back cabinet. It is an unbelieavably good sound, maybe I should plug my 5E3 into that speaker sometime.

tlpruitt · September 28th, 2004, 04:11 PM

Putting aluminum tape on the inside of the back panel helps shield the circuit and should not hurt anything. It also acts as a bit of a heat shield. Many tweed style combos come with aluminum shielding on the inside of the back panel today. The aluminum tape does need to make good contact with the edges of the chassis when the back panel is on the amp though. The holes in the chassis where the screws go that mount the chassis to the amp should be slotted to allow you to adjust the position of the chassis in the cabinet. You need the chassis to sit back in the cabinet so the edge of the chassis is even with the surface that the back panels screw in to. This will allow the back panel to touch the chassis and make good contact with the aluminum tape.

-Tim Pruitt

tlpruitt · September 28th, 2004, 04:12 PM

Putting aluminum tape on the inside of the back panel helps shield the circuit and should not hurt anything. It also acts as a bit of a heat shield. Many tweed style combos come with aluminum shielding on the inside of the back panel today. The aluminum tape does need to make good contact with the edges of the chassis when the back panel is on the amp though. The holes in the chassis where the screws go that mount the chassis to the amp should be slotted to allow you to adjust the position of the chassis in the cabinet. You need the chassis to sit back in the cabinet so the edge of the chassis is even with the surface that the back panels screw in to. This will allow the back panel to touch the chassis and make good contact with the aluminum tape.

-Tim Pruitt

jhundt · September 29th, 2004, 02:35 AM

that was what I thought (aluminum tape would add shielding). I just can't quite understand how the quality of the contact between the chassis and the taped back panel can create such a large amount of noise. There shouldn't be any kind of current on the grounded chassis, should there?

tlpruitt · September 29th, 2004, 03:41 PM

If the sound stops when you touch the back panel it could be because touching the panel pushes the panel against the chassis allowing the aluminum tape to make a better connection to ground (the chassis). The aluminum tape needs to press firmly against the chassis when the back panel is on the amp.

-Tim Pruitt

Rick S · September 29th, 2004, 04:42 PM

Quote:

Originally Posted by jhundt

that was what I thought (aluminum tape would add shielding). I just can't quite understand how the quality of the contact between the chassis and the taped back panel can create such a large amount of noise. There shouldn't be any kind of current on the grounded chassis, should there?

Contact with the shielding material shouldn't have any effect unless it is effecting the signal ground path or a capacitor is leaking DC to the chassis. If DC were the problem, it's likely you would get some scratch when turning the pots. I think that your problem is likely a ground issue.

You didn't mention if your amp has a power cord w/ground (3 prong) conversion. If not, I would highly recommend it. At least, the integrity of the switch and cap should be checked out. If the 3 prong has been installed, but the cap is still in place on the ground switch, remove it. From there, I would take the pots and jacks loose and check for corrosion between the brass plate and chassis and resolder all grounds to the plate and pot backs.

Grounding issues can get pretty whacky.
Rick S

tlpruitt · September 29th, 2004, 05:50 PM

Good points Rick about grounding and leaking DC.

Those old tweed amps can also get wacky when the fiber circuit boards absorb moisture (tweed desease). That's when things really start to get interesting.

10 years ago I built a 5F6a clone with the old style fiber circuit board and after keeping it in my basement for about a year it developed tweed desease. I was pulling out my hair trying to fix the noise and crackling sounds until I figured it out. Those circuit boards in tweed amps absorb moisture and add in the fact that the boards are narrow and the parts are placed relative close together and you get all kinds of mysterious noise and ground issues.

-Tim Pruitt

jhundt · September 30th, 2004, 02:08 AM

I have a grounded 3-prong power cord. But at the moment it is plugged into a 220V-to-120V stepdown transformer and the ground pin isn't in use. This is quite likely contributing to the problem in some way.

Can you explain the reason for removing the cap on the ground switch? I remember hearing about this - isn't this the so-called "death cap"? But I can't recall the reasoning for why it was placed there originally, and why it should be removed.

Rick S · September 30th, 2004, 10:22 AM

When you have the 3 prong installed, the ground lead is attached to the chassis which puts all the circuit grounds at the potential of the ground lead. When plugged into a properly wired receptacle, this puts everything on the chassis, all the way to your guitar strings, at earth potential.

When you take away the ground wire the circuit has no path to earth. In the day before standards required the 3 prong, a path to ground was provided through a capacitor connected between the chassis and the neutral leg of the AC. With this, if you plugged in and didn't get the prong with the cap in the neutral leg it would reference the chassis to the hot leg, the amp would hum and you would have to flip the plug over and plug it in the other way to hush it up.

The ground switch was added as a convenience and it's function is to switch this cap from the hot to neutral leg, preventing the need to go to the wall and flip the plug.

As you can probably see, with the 3 prong putting the chassis at earth the switch and cap serves no purpose. Actually, with the chassis at earth it can only serve to cause hum. The amp will always have the least noise with the chassis at earth.

The "death cap" term came about from the possibility of having the hot AC leg on the chassis if this cap should fail.

Your comment that the ground is not connected leads me to think this is the problem area. Be well aware of possible hazards involving the lack of ground.
Rick S

jhundt · September 30th, 2004, 12:17 PM

Unfortunately, concerning hazards, you haven't heard the half of it! My step-down transformer is an autotransformer. I discovered (after getting some potentially nasty little shocks) that here in Holland it is possible to plug in an autotransformer and your amp will get 120V just fine, only the chassis will be sitting there at 110V instead of ground. We have grounded plugs here, but unlike the US version they can be plugged in right-side-up or upside-down. I have to check the wall socket and make sure I have the plug aligned correctly or it's very dangerous. I am trying to find a proper step-down transformer that will isolate me from this danger, but so far without success.

September 26th, 2004, 12:14 PM	#1 (permalink)
jhundt Friend of Leo's Join Date: Mar 2003 Location: Netherlands Age: 54 Posts: 3,127 9 Photos	5E3 noise cured - but what was the cause? I have an old Deluxe 5E3 - not one of those beautiful replicas. but an old war-horse from the 50's. Many components have been replaced, including most bypass, signal and filter caps. Lately I was getting lots of noise of the snap-crackle-pop variety. It was pretty steady while the amp was being used, only sometimes it would mysteriously stop for a while. I opened the thing up and hunted around for bad connections, components, etc. Couldn't find anything obvious, and the darn thing wouldn't make the noises when I was working on it. Tried different tubes, cables, guitars. That didn't solve the problem. Then I touched the back panel and the noise stopped. Took my hand off the panel and it started again. Touched the panel again, and the noise stopped. When I got this amp, the interior surface of the back panel had remnants of something that looked like asbestos on it. I decided to cover that stuff up with aluminum adhesive tape, which would also help to shield the unshielded side of the chassis. Now it seems that the tape on the panel is not making good contact with the chassis, and somehow this is causing the snap-crackle-pop noise. If I remove the back panel completely the noise goes away, so it's not just stray interference. (In fact, there is a barely audible increase in background noise when I remove the panel, but none of the problem noises). Well now I know what the problem is, and how to fix it. But can anyone explain the science to me? If the chassis is grounded, why should the quality of the back-panel contact create noise?

September 27th, 2004, 01:23 AM	#3 (permalink)
jhundt Friend of Leo's Join Date: Mar 2003 Location: Netherlands Age: 54 Posts: 3,127 9 Photos	Yes Fontaine I love my old amp, and my friends laugh at me because this amp and my others (including home-made stuff) are all prone to buzzes and hums. But I don't mind, mostly. I am attracted by those nice new 5E3 replica kits, especially with a 15" speaker. But I can't afford one. My Fender only cost $50. As far as putting that aluminum tape there on the back panel, I noticed that when Fender changed his amps to a top mount design he put a shielding plate against the open side of the chassis, so I thought I'd try it too. Until this noise started I've never had a problem.

September 27th, 2004, 12:29 PM	#4 (permalink)
fontaine Tele-Meister Join Date: Mar 2004 Posts: 338	Oh Yes! I would love to hear one of these thru a nice 15" Jensen. I believe Lance has one up and running and likes it alot. The one thing i have done is to replace the original spkr. with a p12n Jensen reissue and that was like adding a turbo.Good luck in the never ending tone quest!

September 27th, 2004, 05:53 PM	#5 (permalink)
Lance Friend of Leo's Join Date: Mar 2003 Posts: 2,197	15" Yeah - the 15" rocks! I'm using this as my band amp now and it just sounds amazing. __________________ Lance "not very good...but I make up for it by playing loud"

September 28th, 2004, 02:12 AM	#6 (permalink)
jhundt Friend of Leo's Join Date: Mar 2003 Location: Netherlands Age: 54 Posts: 3,127 9 Photos	My homebuilt uses a 15 I built my home-made "BuzzBomb" (copy of a Vox AC-c0 TB but with only 2 EL-84's) into a combo with an old JBL K-130 (?) in a closed back cabinet. It is an unbelieavably good sound, maybe I should plug my 5E3 into that speaker sometime.

September 26th, 2004, 03:48 PM	#2 (permalink)
fontaine Tele-Meister Join Date: Mar 2004 Posts: 338	The science part i have no clue but i do know that my "54" Deluxe has an asbestos shield also, obviously to provide a heat shield. As far as stickin something metal based where it was not designed to be i think i would not do that. I don't see how it would help anything from a performance standpoint and quite possibly would just act as some sort of RF antennae.But like i said i am no expert and i'm sure somebody here could noodle out the real problem for you. Don't you just groove on the old tweedies? I know i sure do.I can even stand the odd snap or crackle.It just adds to the thrill.Kinda like the same reason i drive an Alfa Romeo.These things have their own personalities!

September 28th, 2004, 04:11 PM	#7 (permalink)
tlpruitt Tele-Meister Join Date: May 2003 Location: Baltimore, MD Posts: 230	Aluminum Tape on Back Panel Putting aluminum tape on the inside of the back panel helps shield the circuit and should not hurt anything. It also acts as a bit of a heat shield. Many tweed style combos come with aluminum shielding on the inside of the back panel today. The aluminum tape does need to make good contact with the edges of the chassis when the back panel is on the amp though. The holes in the chassis where the screws go that mount the chassis to the amp should be slotted to allow you to adjust the position of the chassis in the cabinet. You need the chassis to sit back in the cabinet so the edge of the chassis is even with the surface that the back panels screw in to. This will allow the back panel to touch the chassis and make good contact with the aluminum tape. -Tim Pruitt __________________ Art is making something out of nothing and selling it. FZ

September 28th, 2004, 04:12 PM	#8 (permalink)
tlpruitt Tele-Meister Join Date: May 2003 Location: Baltimore, MD Posts: 230	Aluminum Tape on Back Panel Putting aluminum tape on the inside of the back panel helps shield the circuit and should not hurt anything. It also acts as a bit of a heat shield. Many tweed style combos come with aluminum shielding on the inside of the back panel today. The aluminum tape does need to make good contact with the edges of the chassis when the back panel is on the amp though. The holes in the chassis where the screws go that mount the chassis to the amp should be slotted to allow you to adjust the position of the chassis in the cabinet. You need the chassis to sit back in the cabinet so the edge of the chassis is even with the surface that the back panels screw in to. This will allow the back panel to touch the chassis and make good contact with the aluminum tape. -Tim Pruitt __________________ Art is making something out of nothing and selling it. FZ

September 29th, 2004, 02:35 AM	#9 (permalink)
jhundt Friend of Leo's Join Date: Mar 2003 Location: Netherlands Age: 54 Posts: 3,127 9 Photos	Thanks tlpruitt that was what I thought (aluminum tape would add shielding). I just can't quite understand how the quality of the contact between the chassis and the taped back panel can create such a large amount of noise. There shouldn't be any kind of current on the grounded chassis, should there?

September 29th, 2004, 03:41 PM	#10 (permalink)
tlpruitt Tele-Meister Join Date: May 2003 Location: Baltimore, MD Posts: 230	Touching the back panel If the sound stops when you touch the back panel it could be because touching the panel pushes the panel against the chassis allowing the aluminum tape to make a better connection to ground (the chassis). The aluminum tape needs to press firmly against the chassis when the back panel is on the amp. -Tim Pruitt __________________ Art is making something out of nothing and selling it. FZ

September 29th, 2004, 05:50 PM	#12 (permalink)
tlpruitt Tele-Meister Join Date: May 2003 Location: Baltimore, MD Posts: 230	Ground Issues and Tweed Amps Good points Rick about grounding and leaking DC. Those old tweed amps can also get wacky when the fiber circuit boards absorb moisture (tweed desease). That's when things really start to get interesting. 10 years ago I built a 5F6a clone with the old style fiber circuit board and after keeping it in my basement for about a year it developed tweed desease. I was pulling out my hair trying to fix the noise and crackling sounds until I figured it out. Those circuit boards in tweed amps absorb moisture and add in the fact that the boards are narrow and the parts are placed relative close together and you get all kinds of mysterious noise and ground issues. -Tim Pruitt __________________ Art is making something out of nothing and selling it. FZ

September 30th, 2004, 02:08 AM	#13 (permalink)
jhundt Friend of Leo's Join Date: Mar 2003 Location: Netherlands Age: 54 Posts: 3,127 9 Photos	Rick S - thanks I have a grounded 3-prong power cord. But at the moment it is plugged into a 220V-to-120V stepdown transformer and the ground pin isn't in use. This is quite likely contributing to the problem in some way. Can you explain the reason for removing the cap on the ground switch? I remember hearing about this - isn't this the so-called "death cap"? But I can't recall the reasoning for why it was placed there originally, and why it should be removed.

September 30th, 2004, 10:22 AM	#14 (permalink)
Rick S Tele-Meister Join Date: Nov 2003 Location: Tulsa, OK Posts: 494	When you have the 3 prong installed, the ground lead is attached to the chassis which puts all the circuit grounds at the potential of the ground lead. When plugged into a properly wired receptacle, this puts everything on the chassis, all the way to your guitar strings, at earth potential. When you take away the ground wire the circuit has no path to earth. In the day before standards required the 3 prong, a path to ground was provided through a capacitor connected between the chassis and the neutral leg of the AC. With this, if you plugged in and didn't get the prong with the cap in the neutral leg it would reference the chassis to the hot leg, the amp would hum and you would have to flip the plug over and plug it in the other way to hush it up. The ground switch was added as a convenience and it's function is to switch this cap from the hot to neutral leg, preventing the need to go to the wall and flip the plug. As you can probably see, with the 3 prong putting the chassis at earth the switch and cap serves no purpose. Actually, with the chassis at earth it can only serve to cause hum. The amp will always have the least noise with the chassis at earth. The "death cap" term came about from the possibility of having the hot AC leg on the chassis if this cap should fail. Your comment that the ground is not connected leads me to think this is the problem area. Be well aware of possible hazards involving the lack of ground. Rick S

September 30th, 2004, 12:17 PM	#15 (permalink)
jhundt Friend of Leo's Join Date: Mar 2003 Location: Netherlands Age: 54 Posts: 3,127 9 Photos	Rick S. - the Hazards! Unfortunately, concerning hazards, you haven't heard the half of it! My step-down transformer is an autotransformer. I discovered (after getting some potentially nasty little shocks) that here in Holland it is possible to plug in an autotransformer and your amp will get 120V just fine, only the chassis will be sitting there at 110V instead of ground. We have grounded plugs here, but unlike the US version they can be plugged in right-side-up or upside-down. I have to check the wall socket and make sure I have the plug aligned correctly or it's very dangerous. I am trying to find a proper step-down transformer that will isolate me from this danger, but so far without success.