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Left speaker no sound - tube amplifier

 

Bronze Member
Username: Learners_permit

Post Number: 15
Registered: Jan-12
My left speaker suddenly has no sound. I am using a tube amplifier. Can anyone advise me where to check? I did some troubleshooting by swapping the terminal connections and the left speaker is dead.I look at the tubes while it's on and can't tell which tube maybe giving trouble.
Can anyone assist. Any advise would be much appreciated.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17746
Registered: May-04
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First and foremost, DO NOT run your tube amplifier without a speaker load. Most tube amps will go into self oscillation in short time and will quickly destroy themself if they are not immediately shut down. There must ALWAYS be a load on the outputs when the amp is powered up and you should never try to swap cables while the amp is running. Always power down the amp before you move any wires.


Power down the amp completely then disconnect your speakers. Take a small battery, AAA to 9VDC will do,and hold one leg of your speaker cable against the "-" terminal of the battery. Take the other leg of your cable and flick it across the "+" terminal of the battery. When you have completed the circuit with this flick you should both see the woofer move forward or backward and hear a slight "click" from the speaker. This would indicate your speaker is operational and not entirely "dead".

Does this happen with your left speaker? If you see and hear nothing with the battery test, the speaker is damaged and will require servicing.

Does the speaker respond to the battery test?

If so, the problem is likely in the amp (if you are telling us you think your entire left speaker is nonfunctional). I wouldn't suggest you go poking around too much with a tube amp since the average Voltages inside the amp are somewhere between 400 to 650 Volts. A tube amp holds this Voltage for hours if not days and can still bite you when you think the amp is powered down and unplugged. Servicing a tube amp is best left to a qualified technician.

You can check the tubes - with both speakers connected to the outputs - by giving a visual check in a darkened room. If all of the output tubes are not glowing equally, then a tube might be problematic. If the tubes begin to glow bright orange, immediately shut the amp down and send it to a tech! If the tubes pass the visual test, with the amp powered down you can swap output tubes channel to channel. Observe how the tubes come up to full power for any visual signs of distress. If the problem stays in the same speaker, then the problem is possibly still in the speaker. Test again with the battery. If you determine the speaker is fully functional but after swapping tubes the problem remains in the one channel, other parts of the amplifier might be defective. Stop now!

Since you've told us nothing more about the make or model of the amp, that's as far as I can take you. There are no user serviceable parts in a tube amp and you can quite literally kill yourself by putting your hands where they don't belong. Determine which part of the system needs servicing - speaker or amp - and send it off for repairs.




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Bronze Member
Username: Learners_permit

Post Number: 16
Registered: Jan-12
Jan, thank you for your answering my query. We have exchanged notes before since 2012.
I have done the battery test as advised and the speaker is not "dead". I could hear a scratchy sound the moment it was connected.
There is one tube appears to be much brighter than the rest but I just couldn't possibly tell whether it is a faulty tube. Since the day I bought it and set it up that particular tube seems to be brighter than the rest. I have replaced it to be on the safe side after reading your advice.
My amplifier is a Chinese made 5.1 surround type. The brand is Music Angel.
There are 12 tubes 6AQ5 OR 6N1 and they are labelled V1 to V12. I can't tell which tubes represent Front Left/Right, Rear Left/Right, etc etc. I have attached a photo to show this particular tube (V1) which seems to be bright orange compare to the rest.
The front rows of tube which have bright blue colours are the Voltage tubes 6N2 and I don't think they have any issues.
This morning I have written to the seller for more information to know exactly what does V1 to V12 represent.
Now the next task is to find a qualified technician to service the amplifier.
Will update you on this.
Once again, thank you. Sorry for the picture quality. I can't seem to be able to upload due to the limitations allowed.Upload
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17747
Registered: May-04
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Keep me informed. Small voltage tubes, usually triodes but not always, are likely to have two identical tubes in one envelope. So a very common 12AX7 has two versions of the same tube elements in the same glass capsule. Nowdays it's fairly common for a manufacturer to connect and use both halves of the tube for a stereo amplifier. Identifying which tube is being used in which channel on a mulit-channel amp such as yours would be daunting without some assistance from the manufacturer/distributor. Good luck with that.

If any output tube glows orange, the first suspect would be the bias voltage. If the amp has used adjustable bias, you can try adjusting the bias down. If the amp uses a fixed voltage and only one tube is glowing, you would suspect a bad bias resistor. Though, bias is a circuit and what is in front of the bias resistor might be what's causing the resistor to over bias the tube. So it's not uncommon to need several parts replaced should a fixed bias amp have problems. There are a few reasons a single tube might look different than the rest but, if you replace a tube and a problem persists, then certainly you suspect internal issues.




"I have done the battery test as advised and the speaker is not "dead". I could hear a scratchy sound the moment it was connected."


I assume you have at least two way speakers. What you might have heard would have been the tweeter only responding to the battery. Did you observe the woofer moving with the battery test?



Let me know what happens.


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Gold Member
Username: Magfan

USA

Post Number: 3025
Registered: Oct-07
It should also be possible to swap tubes OF THE SAME NUMBER from side to side.
The previous thought that you dont' know Left tubes from Right tubes will complicate this, but you may be able to at least isolate the problem to a tube.....
 

Bronze Member
Username: Learners_permit

Post Number: 17
Registered: Jan-12
Leo - thank you for your advice. I have swapped the tubes but still it is the same. The supplier has written to me yesterday and I am able to distinguish which tubes represent the front, rear, centre and sub.
Today I have decided to send it to a qualified technician for repair.
Will keep you guys updated.
Many thanks to everyone for their inputs. Much appreciated.
 

Bronze Member
Username: Learners_permit

Post Number: 18
Registered: Jan-12
Hi Jan - Sorry I did not read your 2nd last paragraph.

"I assume you have at least two way speakers. What you might have heard would have been the tweeter only responding to the battery. Did you observe the woofer moving with the battery test?"

Yes I can confirm that the woofer is working fine when I connect an old amplifier which is still working and there is audio from the left speaker.

By the way I have a question to ask regarding Passive Preamplifer. I saw an old thread which you wrote in 2004. Here's the link:

https://www.ecoustics.com/cgi-bin/bbs/discus.pl?pg=prev&topic=1&page=47186#POST95 311

"You must be certain that your souces can drive the power amp to full power. Check output voltage vs. input voltage requirement on the power amp. If the power amp requires 2 volts to reach full power and your CD/DVD will only put out 1 1/2 volts the power amp will not reach full power with a passive design."

I haven't got a clue how to check those voltages. I am using an Oppo BDP 93 player and my amplifier as mentioned earlier in this thread is a Chinese made 5.1 Tube Surround amplifier. I look at the specifications but can't follow.
 

Bronze Member
Username: Learners_permit

Post Number: 19
Registered: Jan-12
Finally I have my amplifier back after sending it away to get it repaired.
It was a very minor fault and all the technician did was to replace a feed resistor.
Set it all up and started playing music and all sounds good.
Glad to have my amplifier back.
Cheers everyone.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17756
Registered: May-04
.

Good to hear, Greenhorn. Generally, if an electronic component survives the first six months, it is good for many years to come. Let's hope this is the end of your problems.
 

Bronze Member
Username: Turnerdaniel770

Post Number: 16
Registered: Jan-14
I agree with you, Good tips for using tube amplifier
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17874
Registered: May-04
.

First, tuners and now, amps. You are the agreeable sort, dan.
 

Gold Member
Username: Magfan

USA

Post Number: 3108
Registered: Oct-07
Tube Amps fail��quite often in predictable ways. You might want to become familiar with the smell emitted when the smoke gets let out of a part as well as what a 'cooked' resistor or capacitor looks like. It'll make your life easier, maybe, in the long run.
Trouble is�..if a part fails�.it can be either the CAUSE or the EFFECT.
If the failed part is the effect of something else going south, than replacing the obvious dead part probably won't help.
You may consider, as part of your tube education, at least being able to CHECK tube bias, without needing to learn to adjust it.

and THAT'S why you are going to end up on a first name basis with some good tech somewhere.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17875
Registered: May-04
.

Most components fail in "predictable ways". It's hardly exclusive to tube amps. The only thing which favors predictability with tubes would be tubes remain a fairly simple technology not loaded down with 128 pin ic's containing a few thousand components not designed to be repaired.

Power supply filters go South in any amp yet power supply transformers remain stable for decades. Coupling caps are seldom the cause of problems yet caps existing in power rails are constantly under stress. Some fool who thinks running the bias on the outputs quite high for better specs is good will end up replacing bias resistors and outputs. In simple circuits, there's not much mystery about why a part fails. Designing in a 1/4 watt resistor when the real world requirements call for a 1/2 watt will ensure failure. The bigger fool who OK's that design simply hopes the cheaper part holds until the warranty expires.

As usual, I'm not a fan of anyone becoming a friend with the inside of their amplifier, most especially not a tube power amp where Voltages remain dangerously high even hours after shut off. A simple thing like not removing a ring before sticking your hands where they don't belong can provide a very nasty surprise. If you have to ask what's wrong, you do not have the skills required to fix what's wrong. Period!


Why learn to adjust bias? There are more than enough high quality tube amps available with auto or fixed bias schemes which never requires the owner to adjust the bias. IMO user adjustable bias does not bring the user closer to the experience of a tube amp. It brings the amp closer to a repair shop due to overzealous and uninformed users with screwdrivers and probes.



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