Hi! I'm new to this Forum, but not totally new to tube amps. I've studied Physics, so I know the general things. And this one's got me stumped:
I bought a tube amp, Trace Elliot Bassamp, running six KT88s. It worked normally and was fully operational, but had ancient caps in the PS and had been tampered with. I did a couple of changes (new caps, new valve sockets...). When powering up all voltages are OK, although it's porely biased (I'm using old tubes for testing, but they're still OK).
Problem:
As soon as I turn ON from STANDBY it squeals your ears off. It only does this with preamp tubes inserted, without those it doesn't squeal, so I guess the power section is OK. Yes, I have tried different tubes. I've got loads of old tubes lying around (ECC83s). So it's not microphonics.
What really makes me curious is: When I switch it OFF (completely disconnect it from the power line) it squeals again, just for a short time, couple of seconds, then gets quieter and dies completely. As if some cap were unloading... Even with the power section powerless it manages the same volume.
WTF?
I bought a tube amp, Trace Elliot Bassamp, running six KT88s. It worked normally and was fully operational, but had ancient caps in the PS and had been tampered with. I did a couple of changes (new caps, new valve sockets...). When powering up all voltages are OK, although it's porely biased (I'm using old tubes for testing, but they're still OK).
Problem:
As soon as I turn ON from STANDBY it squeals your ears off. It only does this with preamp tubes inserted, without those it doesn't squeal, so I guess the power section is OK. Yes, I have tried different tubes. I've got loads of old tubes lying around (ECC83s). So it's not microphonics.
What really makes me curious is: When I switch it OFF (completely disconnect it from the power line) it squeals again, just for a short time, couple of seconds, then gets quieter and dies completely. As if some cap were unloading... Even with the power section powerless it manages the same volume.
WTF?
Your amp is oscillating. The most common problem is that the amplifier's output stage is out of phase. This probably happened when you changed the sockets and inadvertently miswired the the output stage or output transformer primary leads. Assuming this amp uses global feedback, and that's what your description of the problem makes it sound like, try reversing the output transformer's primary leads that go to the KT88 plates. I'll bet this fixes your problem.
If you didn't change the KT88 sockets or mix the transformer wires, then something preceding them has mixed up the phasing. Recheck everything you did very thoroughly.
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Hi HollowState,
Thanks for the answer! The leads from plate to output transformer were correct, but the leads to the grid of the power tubes are reversed (changed position of a circuit board for space reasons) and managed to get them the wrong way round (so the tubes were amplifying the wrong half wave all the time... Never had that before.
One minute of soldering got me my desired result, it works! Without the squeal...
Thanks a lot,
Max
Thanks for the answer! The leads from plate to output transformer were correct, but the leads to the grid of the power tubes are reversed (changed position of a circuit board for space reasons) and managed to get them the wrong way round (so the tubes were amplifying the wrong half wave all the time... Never had that before.
One minute of soldering got me my desired result, it works! Without the squeal...
Thanks a lot,
Max
Hello, new to this site but found this while googeling my issue. Same as above, guitar amp (EVH 5150 III) when switched on from standby a squeal starts, I get a squeal or a "transmisson interference" sort of noise. No work has been done to the amp recently and it worked perfectly last night!? Any help would be appreciated. aholley7@gmail.com
Hi, really, you should start a new thread for this amp, rather than adding on to the end of a thread about a totally different amp. They may move this to the Instrument AMp section anyway.
DO ANY of the controls affect the noise in ANY way?
Does it matter which "channel" is selected?
Go down the row of small tubes, grasping each one tightly. Does gripping any of the tubes affect the noise?
Are we talking about a high pitched shriek? Or a loud hiss like a TV station off the air? (We call that "white noise.")
DO ANY of the controls affect the noise in ANY way?
Does it matter which "channel" is selected?
Go down the row of small tubes, grasping each one tightly. Does gripping any of the tubes affect the noise?
Are we talking about a high pitched shriek? Or a loud hiss like a TV station off the air? (We call that "white noise.")
Not too tightly, please don't go breaking the glass envelope or burning your fingers on hot tubes.
You'd be a lot safer tapping the tubes with the eraser end of a pencil.
Yes, of course be cautious, but most of us won;t cruch a 12AX7 in our fingers. Use a glove or rag if they are too hot. I was indeed looking for microphonic tubes there.
Also, plug something into FX return jack to break the signal path, stop the noise?
And i forget if it has one, but kill the reverb if it does.
Even the resonance/presence controls have no effect?
Also, plug something into FX return jack to break the signal path, stop the noise?
And i forget if it has one, but kill the reverb if it does.
Even the resonance/presence controls have no effect?
Moved to Instruments & Amps per forum policy.faint high pitch squeal from my tube amp
Greetings Folks
Today I was warming up my tube amp before playback, and I reduced the volume to almost zero. I happened to put my ears to the speaker and there was this faint squealing sound with warble. In fact now I recall I heard the same with the volume turned up last week, somewhat louder and over the music but only for like 10 to 15 secs and I assumed it was from some nearby power tool being used across the street.
Attaching a recording of the sound. I put my cellphone microphone right at the cone of the speaker to record it so it is louder in the recording than in real life. If you play it loud enough you will hear the warbling in the whine. It was gone some 30 mins later when I checked again. What do you folks think it is?
Amp is a DIY elekit tu-879s single ended running KT-66s and a 12ax7.
Thanks
G0bble
Greetings Folks
Today I was warming up my tube amp before playback, and I reduced the volume to almost zero. I happened to put my ears to the speaker and there was this faint squealing sound with warble. In fact now I recall I heard the same with the volume turned up last week, somewhat louder and over the music but only for like 10 to 15 secs and I assumed it was from some nearby power tool being used across the street.
Attaching a recording of the sound. I put my cellphone microphone right at the cone of the speaker to record it so it is louder in the recording than in real life. If you play it loud enough you will hear the warbling in the whine. It was gone some 30 mins later when I checked again. What do you folks think it is?
Amp is a DIY elekit tu-879s single ended running KT-66s and a 12ax7.
Thanks
G0bble
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My first thought would be something in your nearby electrical environment being picked up by the amp.
For example here in my shop, I have a wireless phone unit that radiates a pulsing noise. One time the traffic signal at the end of the block had a noisy triac or something and every 40 seconds or so when one particular light was lit, there was a buzzing in high gain amps. And speaking of phones, any number of people have discovered if they set their cell phones on top of their guitar amps, the amp picks up noise from it.
For example here in my shop, I have a wireless phone unit that radiates a pulsing noise. One time the traffic signal at the end of the block had a noisy triac or something and every 40 seconds or so when one particular light was lit, there was a buzzing in high gain amps. And speaking of phones, any number of people have discovered if they set their cell phones on top of their guitar amps, the amp picks up noise from it.
sounds like some computer noise.
if it was constant, I would suspect suspect a firewire or usb interface throwing computer hash on the signal ground.
but since this is intermittent, I am suspecting either wireless ethernet communication device like an Apple TV, Smart TV, Cable Box, or even digital a wireless phone. is too close to your amp.
now if relocating devices does not fix the problem. maybe a revision to the high gain circuit in the amp might be in order. This will involve putting small caps (pf) in the circuit to reduce the rf energy its trying to pick up and amplify.
if it was constant, I would suspect suspect a firewire or usb interface throwing computer hash on the signal ground.
but since this is intermittent, I am suspecting either wireless ethernet communication device like an Apple TV, Smart TV, Cable Box, or even digital a wireless phone. is too close to your amp.
now if relocating devices does not fix the problem. maybe a revision to the high gain circuit in the amp might be in order. This will involve putting small caps (pf) in the circuit to reduce the rf energy its trying to pick up and amplify.
Hmmm .. can we rule out any or both of the issues as a possible cause for the whine that I suspect?
1. Loose contact in input jack/interconnect resulting in grounding short
2. Loose 12AX7 socket - I think this results in loud static and likely not result in a whine.
Both of the above are issues I need to fix.
I am commencing the build of many Felix line filters next week, so we will know if that fixes the hash from the computer by the end of the month.
Thanks for your inputs!
G0bble
1. Loose contact in input jack/interconnect resulting in grounding short
2. Loose 12AX7 socket - I think this results in loud static and likely not result in a whine.
Both of the above are issues I need to fix.
I am commencing the build of many Felix line filters next week, so we will know if that fixes the hash from the computer by the end of the month.
Thanks for your inputs!
G0bble
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