Managing Expectations on Tube Amp Hum

[lootheer]

How much hum should one consider normal in a vintage tube amp? Would these amps have been dead silent when they were new, or did people just have more tolerance for it?

I've been tinkering on and off all summer trying unsuccessfully to get the hum out of a 1960 model year Motorola console (this thread). I have been operating under the assumption that the amp should be dead quiet, or any hum minimized to where it can only be heard with an ear on the speaker. Too often the suggested fix is a radical departure from the original design, such as installing star grounding, new heater wire dress, or DC heaters, all of which suggest the hum is the product of a flawed design and not a faulty component.

I'm considering taking it in to a pro, but only if this amp should indeed be dead quiet when functioning properly. Otherwise, it seems like the fix would be to build a totally new amp in the chassis of the old. What should I expect, hum-wise?

 

[century tek]

Should have no hum. People who might think that some amount of hum is normal probably listened to a stereo while either growing up and/or somehow always hearing a bad one or thought that is the way they are supposed to sound, probably hasn't heard what a proper operating tube amp should sound like.

Check or replace all the power supply electrolytics.

None of my tube amps have any hum. Maybe a little hiss with your ear right up to the speaker, but no hum.

 

[JimmyEJames]

None of my tube amps have any hum. Maybe a little hiss with your ear right up to the speaker, but no hum.

I happy for you but so what?
Depends on what kind of noise
SOME transformers will make little noise some wiring too
Not saying can not get rid of but statement to big and not true
If transformer makes noise then it is going to make noise
Also noise hard to get rid of on some 50 60 year old amp because of wire dress and insulation age noise just radiaitng out of around certain areas and pick up at other
The degree is what matter and sometimes hard to find no matter how good power supply
Not all noise power supply every body think caps fix everything not true
You lucky and I am happy you have no issues! ; - )
JJ

 

[sKiZo]

Oft overlooked is shorting plugs on any unused inputs ...

I'd also do the old wiggle and poke with it on and the cover off. Lots of times, it's just a loose connection. Had that with a multi-cap that had a cold solder joint from the factory.

DO remember, there's some serious voltages inside these things and be careful!

 

[gadget73]

The fact that you get hum with no tubes in it tells me its something either related to the routing of AC power wiring, or maybe its the grounded cord. I didn't notice if you had said whether or not lifting the ground did anything useful for it. You're probably going to be stuck looking at means to re-route power wiring away from signal and speaker wiring.

 

[JimmyEJames]

Too often the suggested fix is a radical departure from the original design, such as installing star grounding, new heater wire dress...........................all of which suggest the hum is the product of a flawed design and not a faulty component.

NOTHING radical about proper wire dress or improving ground and star is best
And poor wire dress or grounding done on production line even from top makers DID happen always SOME BODY'S first day at work!
Poor wire dress is very common especially on cheaper models of machines and machines that were made in huge huge numbers
Have you actual done anything to repair hum issue or still just talking asking what it might be?
JJ

 

[JimmyEJames]

The fact that you get hum with no tubes in it tells me its something either related to the routing of AC power wiring, or maybe its the grounded cord. I didn't notice if you had said whether or not lifting the ground did anything useful for it. You're probably going to be stuck looking at means to re-route power wiring away from signal and speaker wiring.

That other thread is head ache could not read but a little bit but best I can tell transformer leaves making small buzz and this what lootheer hears
I do not know why need another thread to ask same question AND fact that story keeps changing and makes no sense at all lootheer also say this

• The hum is still present when I remove the rectifier
• hum is also present when I remove other tubes, notably the power tubes, one at a time, and all out at once

Well I am NOT expert but that pretty good trick speaker hums with no tube OR rectifier in tube amp
I sorry but this conversation either joke and if not big waste of time unless somebody here can hear what lootheer hear
: - (
JJ

 

[century tek]

I happy for you but so what?
Depends on what kind of noise
SOME transformers will make little noise some wiring too
Not saying can not get rid of but statement to big and not true
If transformer makes noise then it is going to make noise
Also noise hard to get rid of on some 50 60 year old amp because of wire dress and insulation age noise just radiaitng out of around certain areas and pick up at other
The degree is what matter and sometimes hard to find no matter how good power supply
Not all noise power supply every body think caps fix everything not true
You lucky and I am happy you have no issues! ; - )
JJ

I'm not an engineer but even the engineers of the 50's & 60's stereo amps designed them not to have any buzz or hum. I have lots of friends who own Scott, Fisher, Marantz, Magnavox, Motorola console amps and none have hum as long as they are kept up. I think I heard one stock Magnavox with no capacitor refurb. NO HUM!

Now, pretend you're invited to a friends house to listen to an old console his dad left him. It sounds remarkably good but with a hint of hum coming through the speakers between tracks. I do know that that hum is not supposed to be there. It would be annoying to the music!

Now if you are talking about hobby amps built from the ground up or completely rewired, then yeah sure, you will have to chase down hum from bad wiring, bad grounding, power transformer not bolted down tight enough, EMF waves on the chassis...etc,etc,etc.

EDIT: In Lootheer's other thread, I also own one of those Motorola 3 channel amps (6AQ5 version) and it makes no noises. You can't even tell that it is on. Only the can capacitor has been replaced as a few years back it started humming very loudly!

 

[lootheer]

At the risk of feeding what smells like a troll with poor language skills, I am only asking here if I am expecting too much out of old kit and leaving my befuddled newbie troubleshooting behind in the old thread. I do appreciate the advice here, thanks. Time, I guess, to book a time with my amp guy before I do something stupid.

 

[century tek]

Who knows!

 

[primosounds]

Many vintage amps were kits that were first time builds by the owner. That scenario is rife with problems that even the best step by step instructions can not foresee. As is the case with any kid with a new kit to assemble the excitement of assembly and the race to the finish product can lead to errors or sloppy assembly techniques which can result in hum and noise. But fresh factory made products would not have any hum or noise that is greater than the published specs. So, if you have the specs for the amp that is what you should expect from it if it were in as new condition.

 

[rothwellaudio]

It's difficult to say whether or not a certain level of hum is normal because here on the forum we can only go off someone's description, eg "it hums a bit, but not too bad". One person's "not too bad" is another's "unacceptable".

I remember seeing your other thread and it made no sense to me or to many others. A tube amp humming even when it has no tubes in it? Makes about as much sense as a car's engine not running smoothly even when it has no petrol in it.
The only possible explanations I can think of are:
1) connecting the amp to the mains is producing an earth loop with another piece of equipment, or
2) the mains transformer is so close to the speaker that the transformer's magnetic field is inducing hum directly into the speaker - though that seems very unlikely.

 

[gadget73]

Well I am NOT expert but that pretty good trick speaker hums with no tube OR rectifier in tube amp

Not impossible. Its a little hard to do, but it can happen. You almost have to work at it though. If you do something silly like planting the power transformer right next to the output transformer and line up the cores, it'll pick it right up. At opposite ends of the chassis though, its a pretty safe bet that isn't the problem.

 

[ConradH]

My old Dynaco tube amps never hummed, or at least it was below the noise level. OTOH, I've heard a lot of old console amps and such that had low level hum. If they hum with no tubes or without being plugged in, maybe you've got this- https://en.wikipedia.org/wiki/The_Hum

 

[dcgillespie]

A quick perusal of these threads as to the discussion, and an observation: Is there any chance that the power transformer has been replaced on this unit? It surely looks to me like that could be a possibility. In comparison to other commercial products of similar design, it is just massive -- or certainly appears to be so in the pics -- even being much bigger than that implied on the tube location chart. IF that is the case (although it may not be), that brings into the discussion a couple of new factors to consider:

1. Size. Bigger power transformers radiate more magnetic energy for other transformers to pick up.

2. Shielding. The current transformer has no Faraday Shield, which significantly cuts the amount of radiated magnetic energy that the transformer releases.

Again, IF the original power transformer has been replaced with a much larger general replacement part, then a larger transformer without any shielding could certainly cause the hum you are instantly hearing at turn on without any tubes installed, and also aggravate the hum picked up by the inter-chassis cabling as well, making the positioning of those cables much more important in achieving low noise operation. Just a thought..........

Dave

 

[whoaru99]

Funny you mention that...was just thinking, wow, the PT on that thing looks pretty massive, relatively speaking (and pretty clean too). But I didn't know if the size was normal or not.

 

[JimmyEJames]

It's difficult to say whether or not a certain level of hum is normal because here on the forum we can only go off someone's description, eg "it hums a bit, but not too bad". One person's "not too bad" is another's "unacceptable".

I remember seeing your other thread and it made no sense to me or to many others. A tube amp humming even when it has no tubes in it? Makes about as much sense as a car's engine not running smoothly even when it has no petrol in it.
The only possible explanations I can think of are:
1) connecting the amp to the mains is producing an earth loop with another piece of equipment, or
2) the mains transformer is so close to the speaker that the transformer's magnetic field is inducing hum directly into the speaker - though that seems very unlikely.

Thank you!
It did make no sense because more than one version of story
I also work on crossovers sometimes that attach to speakers and I can hear soldering iron transformer through speaker when soldering cap
Guess it all about what is hum?
JJ

 

[JimmyEJames]

At the risk of feeding what smells like a troll with poor language skills, I am only asking here if I am expecting too much out of old kit and leaving my befuddled newbie troubleshooting behind in the old thread. I do appreciate the advice here, thanks. Time, I guess, to book a time with my amp guy before I do something stupid.

Don't know why you say that not true and not nice I think maybe someone who asks question then argues why answer can not work might be troll too so we even then ; - (
JJ

 

[JimmyEJames]

I'm not an engineer but even the engineers of the 50's & 60's stereo amps designed them not to have any buzz or hum. I have lots of friends who own Scott, Fisher, Marantz, Magnavox, Motorola console amps and none have hum as long as they are kept up. I think I heard one stock Magnavox with no capacitor refurb. NO HUM!

Now, pretend you're invited to a friends house to listen to an old console his dad left him. It sounds remarkably good but with a hint of hum coming through the speakers between tracks. I do know that that hum is not supposed to be there. It would be annoying to the music!

Now if you are talking about hobby amps built from the ground up or completely rewired, then yeah sure, you will have to chase down hum from bad wiring, bad grounding, power transformer not bolted down tight enough, EMF waves on the chassis...etc,etc,etc.

EDIT: In Lootheer's other thread, I also own one of those Motorola 3 channel amps (6AQ5 version) and it makes no noises. You can't even tell that it is on. Only the can capacitor has been replaced as a few years back it started humming very loudly!

Design is one thing execution is another
THAT IS WHAT I SAID
Do not need to be engineer to understand value of correct wire dress or leaves vibrating in transformer
Those things and other things too can be incorrect and have nothing to do with design
I know not same thing as audio amplifier but instrument amplifier hum all the time
Listen to this and then understand
All depend on
Design
and
Execution of build
I grow up in 1950s and 1960s my house had Magnavox chairside 1948 and kitchen radio all hum little bit when right in front of speaker
Covered up with music signal
JJ

 

[JimmyEJames]

At the risk of feeding what smells like a troll with poor language skills, I am only asking here if I am expecting too much out of old kit and leaving my befuddled newbie troubleshooting behind in the old thread. I do appreciate the advice here, thanks. Time, I guess, to book a time with my amp guy before I do something stupid.

If serious before calling name post audio clip of sound you are hearing because the story you tell does not add up unless you hearing transformer itself
Maybe if we can hear problem and not just hear you talk about it we can help before start calling people names?
JJ