@ervikingo 

Sorry for the (late night made on cell phone) typos and now repeating myself but please try extension cord(s) to another circut and report back. 
 

“When angry, count four. When very angry, swear” Mark Twain  

Come to think of it, I always have my cell on me and my watch has bluetooth…? in addition to the alarm's cell.

@wsrrsw typing from Phone is always a challenge,  I appreciate your time!

I did try a long extension cord to an outlet which is on a different panel (I have 6 panels at home plus the main panel at the interconnection with the utility).  Problem was present

@ervikingo

When volume turned up does hum get louder?

Both amps on the fritz at the same time?????? Incroyable! …Sounds better in french

Ok. One more improbable guess. Are the mono blocks near one another or the pre amp? I’m thinking power supply interference. As in the PSU on an Amp or the Pre acting up. The hum problem exists using other circuits so it’s cause is something in your equipment.

Got a rubber mallet? Did you try tapping?

“Give a small boy a hammer and he will find that everything he encounters needs pounding.” Abraham Kaolan

@ervikingo 

I'd love to look at the videos you posted, but I don't have Dropbox, and don't want to sign up for even a trial membership. Can you think of any other way to post them? 

After powering up the amps, how long before the hum appears? Does the hum then remain constant for the rest of the time after it first surfaces, or does it come and go? 

the changing glow on the tubes. 

...on all tubes at the same time?

Once the noise starts you can't bias them as the voltage cycles.

I'm not 100% sure, but I don't think that's normal. Of the one stereo tube amp I've had in the past with adjustable bias, I never witnessed anything like that when biasing the tubes. Once the tubes warmed up, the bias values were stable. I've worked on many high power FM transmitters with tubes in the past, and never saw tube bias fluctuate very much there either. Once set, it remained there for a lengthy period of time.

I'd like to thank you @ervikingo for staying engaged in the conversation. Many come to this board, throw out a question or problem they're experiencing, and never show any interest, or offer any feedback after that.  

@ervikingo There are a number of AC line problems that can cause diodes to radiate noise which can get into the audio circuitry. Chief among these is the 5th harmonic of the line frequency (in the US, which uses 60Hz, this would be 300Hz).

Harmonics of the line frequency occur when power transformers upstream from your house are loaded too heavily. If they are loaded past 50% of their ratings is where you get into trouble.

If this is happening sometimes the power company will be willing to replace the transformer if they can find which one is doing it- the 5th harmonic can cause their equipment to run hotter and be less reliable. So it might be worth it to have someone from the power utility to come by and do some tests.

Another way the amps could be in trouble is if the safety ground wire and the neutral wire were swapped somewhere. I've seen this problem happen in the US and it can cause a lot of buzz and hum!

For those interested in monitoring their AC power quality, this is a cool little logger, which can also read some real-time values.

Simple Logger® II Model L261

Hi ervikingo:

Are you using a dedicated line?

Try to twist to single wires between them and connect from main breaker to your amps. This is one way to avoid some frequencies to interfer.

You can also remove ground fir a while from your socket.

Ask for the guy if you are not familiar dealing with electricity.

Good luck!

@dpop thanks to you and all others staying engaged with my dilema. I’ve been at this for weeks.

"After powering up the amps, how long before the hum appears? Does the hum then remain constant for the rest of the time after it first surfaces, or does it come and go?"

It takes 1 to 2 minutes to manifest. Once it starts, it doesn’t go away

"...on all tubes at the same time?" That I can see on all EL34/KT77

I’m going to upload to youtube and post a link

@wsrrsw It ain't Hammer Time buddy!   Noise is present even without interconnects

@atmasphere Thanks for sharing your knowledge!  I'll read more about it.

I have asked the power company to come test their system.  I hope they stick a tester to their lines before coming to see inside.  I'm afraid they might take the easy way out and blame the amps

@pinotnoir it is a dedicated line/breaker to the music room outlets.  These feed the head units,4 monoblocks and a projector.  Keep in mind, Everything but one tube amp is connected at a time as I try to find the problem.

I originally had dimmers (fancy wifi ones) which I took out and replaced with standard non dimmable switches (no dimmers in the whole house now).

As I remove more things from the chain, my mind circles back to what I can't remove: whole house surge suppressor (https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.grainger.com%2Fproduct%2FSIEMENS-Surge-Protection-Device-Three-19T314&psig=AOvVaw2Rhsn6b5q61wEg7Jj_-WGO&ust=1670625130078000&source=images&cd=vfe&ved=0CA8QjhxqFwoTCPC7jNuJ6_sCFQAAAAAdAAAAABAE); Generac ATS and alarm cell.

@ervikingo

I’m going to upload to youtube and post a link

Cool! Thanks!

I have asked the power company to come test their system.

They’ll possibly pull the meter (if they do it quick enough, your generator won’t kick on), check some connections, and they *might* put a logging device on your feed (to monitor your power for a period of time). If you’re around when they get there, they may ask you some questions as to the problem(s) you’re experiencing. Some power companies are also more concerned for their customers needs than others (so be aware). If I remember correctly, most electric companies shoot for 120/240 volts +/- 5 volts. If your voltage fluctuations are within that tolerance, they might ask you then to call an electrician, and have your internal wiring checked out. Technically your local power company is typically not responsible for anything past the meter, so most times they won’t want to enter the property if they don’t have to.

Unfortunately, the link you provided above does not work. I’m guessing it’s for a surge protector you’re using.

I notice that you have an ATS, but yet the SS amps are quiet with it. Would I be correct in stating that the hum is in sync with when the amp puts through audio (ie, the hum starts at the exact time the amp has warmed up, and is now passing audio)?

I have to ask this question. To hear this hum, are you putting your ear against your speaker, or can you hear it from 3’ away?

I’ve been at this for weeks.

Hum drives many audiophiles a little crazy, because many of us spend thousands of dollars on equipment, expecting after hooking it all up, to have dead quiet backgrounds. As frustrating as it can be, that unfortunately is not always the case.

and a projector

Does unplugging the projector have any effect?

@dpop my house was built 5 years ago but the transformer has been there for years (i had the lot for 15 years before i built). Hopefully they’ll come check properly.

The surge suppressor: https://www.grainger.com/product/19T314?gucid=N:N:PS:Paid:GGL:CSM-2295:4P7A1P:20501231&gclid=CjwKCAiAs8acBhA1EiwAgRFdw5vydJ0e_aoebliMyysBdXlqJr17jYErMuOOzINNmRQI1B3De8g-EhoCJyIQAvD_BwE&gclsrc=aw.ds

Yes the SS amps are totally quiet. The hum starts when the amps start to put sound. I can hear it 12 feet away...

FYI, there is no mechanical noise on the amps. Just the noise coming from the speaker drivers

No changes with or without the projector plugged in.

holmz    I didn't say it might be a ground loop, although it may be.

I did not say you did.

I said it. 😎

If OP reports correctly the hum is exactly 60Hz, the coincidence is too much.

If we had an Ishikawa chart we would see that a ground loop is  on the list of causal mechanisms. But we have possibility of one without the RCAs connected.

So that leaves incoming power, or the amps are jacked up, or some high current magnetic field near the amps... or ???

That's why I suggested to test the rig in another location

That helps identify the power and magnetic field.
If it sucks in location #2… then it points stronger to the amp being jacked up.

Power Conditioner in use or available to try?

@wsrrsw tried with Van Alstine Humdinger (for DC) but as described by FVA it only works to solve mechanical noise. I decided to try anyway. 
 

Also tried the iFi plug in things and even an old Tice thing (not the digital clock)  

waiting on a Zen Line Conditioner from Decware. 
 

Tomorrow planning on shutting down the alarm’s cell and wireless sensors. 
 

I went into the circuit breaker panel to confirm ground are properly connected. 
 

Next is taking amps to test at my office. 

what am I missing?

I suspect that it is the filter capacitors in the power supply. I used to fix tube TVs when I was a kid. 
 

You could also try an isolation transformer. 

Well, I can confirm it is not the alarm (which BTW I have reconnected!)

@redhouse6 like a Triplite?

I have a ZLC on order but it takes time to get it.

ervikingo

... Next is taking amps to test at my office. 

I think that will reveal the amps are the source of your problem.

ervikingo

... Next is taking amps to test at my office. 

+1

A shot in the dark here, have your output tubes been cryogenic treated?  I had a set of cryogenic treated KT88’s develop loud hum.

@ervikingo I had assumed that since your amps were 'tested at the factory' that they had a clean bill of health. But the first rule of troubleshooting is 'don't make assumptions'.

Occam's Razor is always trying to get me to look at the simpler explanation, and @redhouse6 's comment about the filter caps is a very good one! A lot simpler than most the other explanations here, including my own.

So how old are your amps?

The responses I read all seem helpful.  I had a LF hum that drove me crazy. Don't know if this is relevant to your situation, but mine was caused by interference from my wireless router that was close to my equipment stack.  The router was at the same level as my TT and the interference was picked up by my Lyra Kleos cartridge.  I relocated the router to a lower height and across the room and it was gone.  Go figure

Yes, like a Triplite.  They make quite a few different devices and sizes, so I don't know the specifics of the one you are speaking of.  I bought a Triplite to isolate some testing equipment I was working with on a train.  

Bringing your equipment into your office or a friend's house will be the free option.  I would try that first, before purchasing anything.  

@atmasphere they are 20 years old.

I just realized that the prior owner changed the input tubes to 12AX7 when the design calls for 12AT7.  Thus higher gain (if my limited knowledge of tubes is correct) than what the spec for my particular version of these amps calls for.

Could that cause the oscillation?  I ordered a couple of AT7s to swap.

Regarding the factory and I quote: The unit was biased and received a complete test.  Unit passed all factory specs.

@rhljazz Not treated.  Thanks for the suggestion

@papafrgog the closest access point is 20'away.  I disconnected all wifi and low voltage and it didn't improve.  Thanks!

@redhouse6 I agree, I'll try on another location before buying something else.  I have a collection of tools and tweaks which is getting expensive.

Hoping the upcoming input tube swap finds the issue.

With your tubes or tube the OE/Tester had?

 The unit was biased and received a complete test.  Unit passed all factory specs.

@jerryg123 Can't confirm.  Good question

If your amp has them, make sure to run the rear impedance selector switches in the 15K position (it looks like not all Snapper models have them).

It’ll be interesting to see if installing 12AT7 tubes has any effect on the hum. I think it will.

I just stumbled upon a review of the amp:

Soundstage.com Home Audio Equipment Review

Here’s a few opinions on substituting 12AX7’s for 12AT7’s:

Can I substitute a 12AX7 tube for a 12AT7?

Well I had problems with hum on mine,, Try using an extension cord and plugging them in on other circuts

The substitution of the the 12at7 or Whatever might have something to do with it.

@hiend2 

Try using an extension cord and plugging them in on other circuits

ervikingo has tried that already.

I has a trouble in my preamp similarit was exposed to a Large Magnetic field.

Take the amp to your office,

Try a solid state unit...

@ervikingo Hate to say it but I keep thinking about your neighbors WiFi transmitter system. 

I spent 20k on buying 2x PS Audio P20 AC regenerators and I still have a hum. Also it is rare that 60hz is the only frequency usually you get a lot of 120hz the harmonic. Test to see your ground and neutral voltage should be very low if it is anything above 1 or 2 volts that could be it. Also a new TV or radio station in the area. I love tube amps but I'm thinking they are such a pain. 

@hiend2 

Try a solid state unit...

ervinkingo has tried that already, and the solid state amps don't hum. Please look back at some of the past comments.

@donavabdear 

I love tube amps but I'm thinking they are such a pain. 

I agree with you, and that's one of the reasons why I no longer incorporate them into my systems.  

@ervikingo 12AX7s trade high impedance for more gain so could be sensitive to a variety of variables. So going to 12AT7s may well solve the issue. 

I've also found that the brand of tube can sometimes cause hum. For example a phono section I was working on exhibited a hum a few minutes after warmup. The customer had replaced the stock 12AX7 tubes with Brimars, which are supposed to be a nice tube, but for some reason, even though the filament supply was regulated DC, the tubes would hum. Replacing them solved the problem.

@dpop thanks for adding my comments and past attempts.  Those links are very useful !  The reviewer said they are dead quiet.  Hoping I get that

@hiend2 @donavabdear thanks for the input

@atmasphere Can’t wait to get the tubes here. In hopes of staying away of issues like you mention, I ordered them from Manley.

Sure hope that solves the problem. I have tried so many things and never looked at that detail. Sometimes the simplest answer is the best one.

Sometimes the simplest answer is the best one.

Yes- if more people understood Occam's Razor the world would be a lot calmer place to live.

I wholeheartedly agree.  Funny, one of my bicycles is an Orbea "Occam"

Thanks for all your insights.  I'll post results after replacing the tubes.

I had this issue for years.  Turned out to be my Rel subwoofer.  I grounded it to the preamp and it disappeared.

@ervikingo

When it comes to AC power, audio gear, or electronics or electricity in general, I have never seen or heard anything like that ever before. Thanks for sharing the video! Wow, WHAT is going on here? And both amps do this?! Plugging one of these in at a completely different location should also tell us something. Has that been tried yet?

@jea48

did you start up the generator and transfer the load of the ATS to generator? You would be off line of the Utility Power Co...

Great suggestion! Since you can’t just pull the electric company meter to simulate a power outage, the ATS would need to have a special function switch to power up and transfer the load. Not all ATS’ have this switch and function, but it’s worth a look. Many generators and ATS’ have test switches, but don’t always transfer the load.

@stevencason

I had this issue for years. Turned out to be my Rel subwoofer. I grounded it to the preamp and it disappeared.

Crazy.

@jea48

Are you sure that is the whole house SPD, (Surge Protection Device) you have?

Good call! Let’s see. Hopefully it’s the TPS3A11 version, if the service drop is single phase.

Siemens TPS3 External or Wall Mounted SPDs

The sound in that video sounds like “motorboating”.

@holmz

 you beat me to it...

@dpop

It kind of sounds like a low frequency motorboating oscillation.

This may be off the wall, but I seem to remember reading a thread several years ago, can’t remember if it was on Agon or AA where a guy was having an oscillation problem with a tube amp. Just going from memory someone asked what speaker wires he was using. What ever manufacturer, type, speaker wire it was it was causing an impedance mismatch for the output transformers for the amp. If it was here on Agon I would bet the Late @almarg chimed in and was the one that solved the problem.

Might be worth it to try a cheapo zip cord 14/2 cable and find out for sure.

That happened to me a month ago,  I heard the hum through both of my speakers, very annoying.    That hum noise was from my KT88.    Later I swapped my tubes to another KT120.    Noise is gone,  so quiet.     That was my fixed.  Nothing related to any ground, power conditioner.

If you have extra set of tubes,  try swap it and see if that helps.

@jea48 

speaker wire it was it was causing an impedance mismatch for the output transformers for the amp.

Wow, these tube amps are more sensitive then I thought. Come to think of it, I was really into tube headphone amps for a while. I discovered that they too were very sensitive to headphone impedance, when it came to low level hum produced by the amp. I weighted the issue, and concluded that the headache just wasn't worth it. I was also many times hearing sporadic plinks, plunks, and noise bursts with tubes, and that drove me a little crazy too.