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Hum- help needed

It's been very strange and I cannot think of a logical explanation.
It will require all your attention.
1. Two mono blocks plugged in. EVERYTING ELSE IS UNPLUGGED,
ICs disconnected- hum in the R channel (can be heard from
2-3 ft. away)
Hum in the L channel- order of magnitude lower, I would consider it "normal", can only be heard with the ear to the driver.
So I would think, it's not a ground loop (nothing else is plugged in, heard in R ch. only.
2. R Amp. moved to the L speaker (other amp unplugged altogether)- no hum.
L amp. (used to be quiet), connected to the same L speaker, with the same power cord- hum.
3. All tubes switched L to R- no difference.
4. R amp moved back to the R speaker (position, where it used to hum- no hum.
5. L amp (used to be quiet)- hums, no matter what.
To sum it-up:
I think it's not a ground loop (see #1),
It's not the amp.- (see # 2),
It's not a speaker- (see # 2),
It's not the tubes- (see # 3)

So, here is my question- what the hell is it?
maril555
tvad
9,467 posts
 
It hummed BEFORE and AFTER I swapped the tubes, and hummed again after tubes were in the original position, in other words, tubes swapping didn't affect the hum.
Maril555 (System | Threads | Answers)

Understood. Good luck.

FWIW...when I have had a hum in one tube amp and not in the other, it was because either a power tube required re-biasing, or a power tube was bad.
plato
1,543 posts
 
If you changed the "bad humming" amp to a different circuit and it was quiet then I would suspect that the outlet you are using for your stereo may not be properly grounded or may be wired improperly. Any electronics store should sell a simple outlet tester for less than $10 that will instantly tell you if the outlet is properly grounded and wired correctly...
tvad
9,467 posts
 
10-07-07: Plato
If you changed the "bad humming" amp to a different circuit and it was quiet then I would suspect that the outlet you are using for your stereo may not be properly grounded or may be wired improperly.

Precisely. That's why I asked if the same outlet was used for all the swapping, or if two different outlets were used.

The tester Plato mentions is handy to have. It will also check for proper polarity.
maril555 OP
618 posts
 
Plato, Tvad- I agree with you, and also think, that the problem is with the outlet. Actually I have an electrician coming tomorrow to install two extra lines, and I will have him check the existing one, as well.
All that said and done, the most puzzling part to me is, that hum went from one amp to another. I can't even contemplate a reasonable explanation for this one.
jea48
2,944 posts
 
1. Two mono blocks plugged in. EVERYTING ELSE IS UNPLUGGED,
ICs disconnected- hum in the R channel (can be heard from
2-3 ft. away)
Ics disconnected. Amp and speaker totally isolated from other Amp?
>>>>>>>>>>>>>

2. R Amp. moved to the L speaker (other amp unplugged altogether)- no hum
#2. Test, was L speaker cable still attached to L speaker and then R Amp connected to (L speaker cable and L speaker?) (L speaker cable/L speaker, a constant test control unit)
>>>>>>>>>>>>

L amp. (used to be quiet), connected to the same L speaker, with the same power cord- hum.
Was L speaker cable still connected to L speaker?
In other words for your tests did you always keeps the speaker cables mated to the speakers they were originally connected to?.......
>>>>>>>>>>>>>>

L amp. (used to be quiet), connected to the same L speaker, with the same power cord- hum.
>>>>>>>>>>
Just a shot in the dark, Could it possibly be a cable impedance problem? A problem with a Speaker cable?

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