Hum is most likely coming from a Transformer not a tube.. |
+1. Almost certainly transformer. Do you hear the hum when you're close to the unit, through the speakers, or both? Any which way, transformer. Could be DC on the line, could be ground loop, could be a transformer that hums. (Other manufacturers when asked have replied: yes, they do that.) |
First, please clarify whether you are talking about a mechanical hum coming from the unit itself or a hum that is audible on your speakers. If it's a mechanical hum, I agree with the above two responders. You could try tightening down on screws that hold the transformer laminations together, if the transformer is not potted. Or you could isolate the transformer from the chassis on rubber grommets. Neither is guaranteed to work but might work.
If it's a hum on the audio signal, then the issue is mostly likely due to equipment grounding, not a tube, although it's also possible you have a dirty tube socket. All that said, if you've never changed the tubes since the 90s, it's probably a good idea to do that too. |
I would definitely replace those tubes even if it is not the source of your hum. You will greatly improve your enjoyment going with different brands. Both of those brands you mention make very poor sounding tubes in my humble opinion. Call Andy at Vintage Tubes services as he will be able to recommend the brands for the sound quality traits you desire. |
Thank you for all your responses. Dealing with the transformers is beyond my pay grade. Does anyone have a suggestion on where I should send the amp for professional repair? I live in the northeast US but would be willing to ship it anywhere.The company that made the amp no longer exists so that isn't an option. |
I guess you've chosen not to respond to my question about the source of the hum. If you don't know what's broken it will be difficult for a repair shop to fix it. If the problem is due to AC grounding in your system it may not exist when the unit is in a repair shop, for example.
Anyway: Bill Thalmann at Music Technology in Springfield VA is the best on this side of the Mississippi
Weve established that if the tubes have never been replaced now is the time.
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Tubes can 100% absolutely positively hum! I used to use Sovtek tubes and they were horrid, many hummed like crazy. New Electro Harmonix are much better. NOS US made are best and quietest. I definitely recommend getting new tubes to try.
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What made/model is the amp? As already said, there's a strong chance there's nothing to repair. If you send it anywhere, have a good long talk with the repair person before you send it. The problem may be inherent in the AC coming into your house, in the wiring of your house, or in the model or unit itself. Lots of variables... |
2leftears, Most likely, it would be the ground scheme of the audio system itself and what is plugged into what receptacle and/or how any one piece of gear is grounded internally (some mix chassis ground with signal ground; some isolate one from the other), but you're basically right.
Invictus, Please tell me in what way your anecdotal report proves that tubes per se can be a prime cause of "hum"? Let's be clear also, that when one uses the term "hum", it typically refers to 60 Hz or 120 Hz noise. Tubes certainly can be noisy, especially aging tubes, but when they are noisy it's usually a mixture of many frequencies, which sounds quite different from "hum". So, I guess a grossly defective tube that is shorted out could play a role in causing horrendous hum, but in that case you'd get no music at all.
Anyway, maybe the OP will come back and explain his problem more clearly. |
I thought of one way in which a tube could cause classic hum as I defined it above: If you have an AC filament supply and especially if you are powering Directly Heated Triodes (DHT), the AC on the filament, which is also the cathode in a DHT, can be amplified and produce audible hum. However, the cure is not to replace the tube but to fiddle with the filament supply or change over to DC filaments. |
@jcbach , does your amp use a 3-prong power cable; the type with an earth ground? If so, try using a cheater-plug into the wall receptacle. This will eliminate the possibility of a ground loop. |
@lewm My experience proves it. Had an integrated tube amp which used 6SN7 tubes. Ordered brand new Sovteks from Parts Connexion at the time and they hummed so bad it was impossible to listen to music. 60Hz hum and noise/buzz on top of it.
Replaced them with JAN 6SN7 and it was so quiet you’d have to put your ear to the tweeter to even hear the faintest of hiss.
Yes, garbage Russian and junk Chinese tubes can hum.
I had a similar experience with 300B tubes and many others. |
Thank you for all your suggestions. lewm the sound is through the speakers. I've been told that tubes after 10 years should be replaced as they might draw way higher current and create a stress on the power supply and create hum. I've also been told that transformer noise is mechanical noise and would not be heard in the speakers. It seems like replacing the tubes is the initial way to go as the tubes I currently have don't seem to get high marks anyway. |
10 years! Seems that it´s time to replace the tubes, no doubt about that.
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I've said all I can say. Good luck. |
6SL7s made in Russian often have leakage problems (this is a test on a tube tester) which can introduce hum. We've had such troubles with Russian-made 6SN7s (which are similar but less gain) that we've had to recommend on our website to simply not use them.
OTOH I've yet to see a Russian power tube do that. So yes, you can use other tubes and I recommend it. I would make sure though that the new 6SL7 you use is tested for no leakage on a good tester.
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@analogluvr I contacted Andy at your suggestion a few days back through his website and shared what I have for tubes as well as the issues. Still waiting for a response. Not sure if he's on vacation or just not interested :) |
