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Tube amp + speakers: after a while, sound begins to cut out regularly, Was: Sound blips (TOS #6)
MrCogline
post Dec 18 2011, 00:43
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Hey guys iv'e got my tube amp and everything set up but i have this problem!

There is a weird sound blip that goes on my speakers it's like the sound stops for half a second then resumes and does this again 3 secs later on both my speakers so it's like pulsing between the two, is it the tubes becomes it doesn't do this when you first turn on the amp.
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Apesbrain
post Dec 18 2011, 21:31
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When the music "blips" does it pick back up exactly where it left off or a half-second worth of music later? The former would indicate a problem with your music source, e.g. CD/MP3 player or computer.

If it is the latter, then what you are describing sounds like a protective circuit in the electronics activating. This happens so the user is warned of a potentially fatal problem before the gear or anything attached to it self-destructs. It could be an electrical (short) or thermal (overheating) fault. Since it starts "blipping" after the gear has warmed up, that hints at a thermal problem. Do you have the tube equipment in a place where it receives adequate ventilation? For example, it should not be in a small, closed cabinet. What is the ambient temperature in the room where the equipment is located?

Given your unfamiliarity with equipment like this, however, it is likely that something is wired improperly creating a short. Can you post close-up photos of the back of all pieces including the speakers showing how you currently have them connected? Post a picture of each of the connecting cables.

It may also be that one or more of the tubes or other electronic components are not operating properly or within their normal electrical range. Something may have been damaged or misaligned during shipping or someone removed the tubes and did not put them back in their correct places. This is best left to a professional to diagnose and repair.

Your problem may in fact be with your power source. How are the pre-amp and power-amp connected to mains power? How many power strips are in the circuit? Try connecting these components directly to the wall outlet. If this is already the case, try another wall outlet.

Lastly, you can always attempt to contact the company or you may find some knowlegeable owners in this forum. Better yet, find someone locally who knows something about equipment like this and offer them a few Guinness to come over and help you.

Avoid operating the system until you have some suggestions on how to correct this problem or until you take it for service. Reasonable people can disagree over whether $5000+ worth of tube gear sounds any better than a $150 solid state receiver but you can't deny it costs a lot more to repair the former if it blows up.
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MrCogline
post Dec 18 2011, 23:45
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Thanks for the reply, and sorry for the bad sentence structure, it was posted while i was intoxicated.

Right so to better describe the problem i have it's the sound cutting in and out every 3 secs on each speaker, and when i have volume turned all the way down my speakers pad thing moves in and out like when you see a sub woofer play some really low frequency's.
I'm temped to leave amp on and eliminate the input signal (so unplugged it from my PC) to see if it's the input or amplifier itself causing the problem. I have a suspicion it may just be the tubes as they make a sort of ting when the sound cuts out. The tubes are over 5 years old btw!

The tubes may also be in the wrong places. I'm going to buy new ones, where and how should i purchase them? They need to be "Matched" to work correctly right and do i need to bias the amp for these new tubes?
Finally how do you know which tube goes where!? or are the assign a certain slot after being biased with the amp?
anyway.
Thanks much,
Jake

This post has been edited by MrCogline: Dec 18 2011, 23:46
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soulsearchingsun
post Dec 19 2011, 14:32
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QUOTE (MrCogline @ Dec 17 2011, 17:38) *
Any ideas why?

I'm sorry to say, but this sounds like an electrical problem within one of your devices. Try to rule out defective cables, try another power amp if you happen to have one on hand to see whether it's the pre- or the power amp (likely it's the power amp that has a failure). But it's near impossible to say anything specific about this defect from afar. IMHO it's rather unlikely to go away with new tubes, but I haven't had many tube amps between my fingers yet, so I could be wrong.

edit: Huh? What happened to this post? Weird.
edit2: replied to the question in the other thread, got moved here.

Don't buy new tubes unless you definitely know the problem IS the tubes. You might ruin the new ones directly if something is misbehaving internally. Don't use the amp as it is, it might kill your speakers, depending on how much energy is fed to the speakers. Apart from that, I agree with apesbrain's suggested solutions. Find someone knowledgable or contact the manufacturer. I don't know much about matched tubes and biasing, but as I said, see someone who can check your amp first anyways.
Keep in mind that the sockets need to be rewired if you buy E80L types, they aren't direct replacement types.

This post has been edited by soulsearchingsun: Dec 19 2011, 15:06
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MrCogline
post Dec 19 2011, 19:27
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Hi if you guys just want to take a look at this video i better explain my problem.

http://www.youtube.com/watch?v=mr7WhOWCxi4...D3oCn1RVLh1rKdR
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MrCogline
post Dec 19 2011, 21:24
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I opened the guy up and there seems to be nothing obvious that is broken inside so maybe a transformer or maybe just the tubes...?
Maybe even the preamp! don't know.
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DVDdoug
post Dec 19 2011, 22:49
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QUOTE
I opened the guy up and there seems to be nothing obvious that is broken inside so maybe a transformer or maybe just the tubes...?
It could be a tube, but probably not a transformer. Sometimes you can see something burned or something loose. Sometimes you can wiggle things around to see if there's a loose connection (but beware of high-voltage!) But, since you can't see the electrons, it usually takes a schematic, oscilloscope, and multimeter, and possibly some electronics knowledge and a service manual... and possibly the tools & abiity to solder.


QUOTE
Maybe even the preamp! don't know.
If the preamp is separate, you can disconnect it. If the preamp is built-in, the volume control is between the preamp-stage and the power-amp stage. If the noise & speaker-pumping go up-and-down with the volume control, the problem is in the preamp-stage. (If the problem is in the preamp-stage, turning the volume all the way down, should block the noise.)

If you are getting this defect in both channels (with nothing connected to the input), it's probably the power supply.

QUOTE
The tubes may also be in the wrong places. Finally how do you know which tube goes where!?
The owner's manual!. Any tubes with the same part number can be interchanged (although the pairs may no longer be "matched"). The tube number is usually marked on the chassis, or there should be a diagram on a "sticker" on the back or bottom of the amp. You might need to take it to a repair shop that has a service manual. But it might need to go to the shop anyway... If the repair shop has a tube-tester, they can also tell you which tubes are best-matched. (Do they still make tube testers????)

QUOTE
...or are the assign a certain slot after being biased with the amp?
No. Unless they are the same part-number. There are usually different tubes for the input-stage and the output stage. There may be 4 output-tubes (2 per channel) and these should all be the same tube-number. It shouldn't matter if these "identical" tubes are mixed-up.

QUOTE
I'm going to buy new ones, where and how should i purchase them?
I'm sure you can find them online, or at an authorized repair shop for your amp. Parts Express sells tubes. Depending on the price of the tubes, it might be cheaper to get it repaired professionally. If problem is not a tube, you'll end-up paying for tubes plus a repair... If it's unrepairable (or not economically repariable) , you'll end-up with a bunch of new tubes and a dead amp.

QUOTE
They need to be "Matched" to work correctly right and do i need to bias the amp for these new tubes?
You can buy matched pairs (or matched sets of 4).

IMO a "good design" should tolerate any tube (of the correct part number) that meets it's specs. With a good design, you shouldn't have to buy matched sets or adjust the bias.

I believe tube-matching is usually done for performance purposes... Not to prevent an outright failure. But again, a good design should perform well without selecting/matching tubes and without adjusting the bias. (Solid state devices vary too... But a good design is independent of these variations, and all of the amps coming off the assembly line can have similar-excellent performance.)

The tube's characteristics are going to change as the tube ages, so hopefully you don't have to re-match tubes or re-adjust the bias every year or so... If you have to adjust bias, I assume that requires you to measure the current or voltage at a test point. You'd need a multimeter and a service manual.



biggrin.gif P.S. It's almost 2012! Maybe it's time to leave that 1950's tube-technology behind and move-up to something more modern, more economical, more reliable, and more energy efficient! biggrin.gif

This post has been edited by DVDdoug: Dec 19 2011, 23:05
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MrCogline
post Dec 21 2011, 19:04
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Hi hi,
need some help on identifying a problem i may or may not have with my tube amp and preamp.

The speakers cut out for a second and spring back into life until this happens again 3 seconds later. This happens in both speakers at different times. It doesn't start immediately after turning my tubes on but a minute later . The soft pad where the sound comes from will go in and out as if it's playing a really really low bass note one speakers usually starts before the other. Even if i cut off the signal from the pre amp this still happens. Making me think the problem is in the tube amp.
What could cause this?
My thinking is maybe just some bad tubes, possibly a discharging capacitor?
Possible thermal problem? but i would think that a break in the circuit would stop all sound all together but sound comes out from one channel at all times.

any thoughts on how i could identify this problem?
I have multimeter and probes ready but no tubes i know "work"

The tubes I've got in at the moment are real old.. my dad said one of the power tubes blew and he hasn't used it since.

I've opened the back up and nothing jumps out at me that it's broken maybe i should have the back open and turn it on?

The tube amp i have is the Unisis with the prophet pre amp both from Tube Technology and the speakers are Sonus faber Electra speakers. Here are some pictures.

http://imageshack.us/g/266/pc200048i.jpg/

Tell me if link doesn't work!

Thanks,
Jake.
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pdq
post Dec 21 2011, 21:19
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When you say "one of the power tubes blew", I assume you mean one of the output tubes (the big ones, there should be four of them). Are you saying that you are trying to operate with a blown tube, or possibly with this tube removed?
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MrCogline
post Dec 21 2011, 21:24
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It was one of the Power tubes one of the two that are at the front !

and I'm pulling each of the output tubes and playing it to see if it's a faulty tube atm (which i think it's not)

http://www.geofex.com/ampdbug/popping.htm

I think it's something like one of them causing it there is a popping sound when the sound cuts off.
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pdq
post Dec 21 2011, 21:42
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Never remove just one output tube. Always remove them in pairs.
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MrCogline
post Dec 21 2011, 21:43
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so if i have all 4 on the right side and only 2 on the left is that okay?

and why remove them in pairs?
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greynol
post Dec 21 2011, 21:49
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If it's a push-pull design, then yeah more harm is being done than good with reckless attempts at troubleshooting.

Find someone to service the damn thing. Providing pictures is rarely, if ever going to reveal the true source of the problem. Contact a store that sells musical instruments, they should be able to refer you to a person who knows how to service tube amplifiers. Make sure you get an estimate, since you'll likely find something that provides more accurate reproduction and is far more reliable for the price you'll likely have to pay to get the amp repaired.

I fear that you're in way over your head and could even get yourself killed.

This post has been edited by greynol: Dec 21 2011, 21:50


--------------------
Your eyes cannot hear.
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MrCogline
post Dec 21 2011, 21:53
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okay noted.

I'll have to wait for nearby contacts to get back to me then,

Thanks for all your help! biggrin.gif
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pdq
post Dec 21 2011, 22:25
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QUOTE (MrCogline @ Dec 21 2011, 16:43) *
so if i have all 4 on the right side and only 2 on the left is that okay?

and why remove them in pairs?

The two output tubes operate in a fairly efficient class AB mode. When you remove one tube you are now in a much less efficient class A mode, which means the power consumption could go way up, causing the power supply to cut out, or even causing serious damage.

Please look around at what $200-300 can buy you in a nice solid-state amplifier or receiver.
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MrCogline
post Dec 24 2011, 21:55
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Sucks no one in my local area can really help me with this.

... sad.gif
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