FBT 200 - strange noise

[vintagekiki]

I was able to damp the noise with a gloved hand, but nothing else seemed to work. I tried re-tensioning the tube socket pins and retainer clip to no avail, and nothing we had on hand seemed to help.

PT transfer own vibration to the chassis, and this vibration via tubes socket transfer to the tubes.

It happens over time that the electrodes in the (old) tube slightly mechanical relax , and some of the electrodes (g1, filament ..) start to vibrates. This manifests as a sound sensation in the amplifier. The only solution is to replace this tube.

[SoulFetish]

PT transfer own vibration to the chassis, and this vibration via tubes socket transfer to the tubes.

It happens over time that the electrodes in the (old) tube slightly mechanical relax , and some of the electrodes (g1, filament ..) start to vibrates. This manifests as a sound sensation in the amplifier. The only solution is to replace this tube.

I don’t doubt that this happens. But its not what happened in this case. All of the tubes were new, and it wasn’t oscillating at mains or rectified frequencies. I suspect the speaker/upside down mounting in the combo amp setup had more to do with the problem in this case

[pamelahute]

Hi guys. I continued the tests.

So the rectifier created the problem for sure, but if I keptthe old EH EL84 I had installed, the vibration was still there.
I had to change all three the get rid of the issue.

Here's a quick clip of me playing the notes which were generating the vibration (E / F mostly) - https://www.dropbox.com/s/dd3ivilcsu...honia.mp3?dl=0

If you listen carefully, you can still hear a tiny thing but it's nothing compared to what it was.

[vintagekiki]

If you listen carefully, you can still hear a tiny thing but it's nothing compared to what it was.

Your amplifier is a music amplifier, it's not a HiFi amplifier.
The best way to see if an amplifier is working properly is to compare it (one to one) with another amp of the same model. (FBT 200 to FBT 200)

[pamelahute]

i know it's not hifi haha ! of course ! I'm used to noisy vintage stuff
You heard the initial noise on my sound clips, I was really complicated to use, even for musical purposes and especially for recording.
Now the amp can totally be used normally and musically.
I don't think I was over reacting in the first place...! was I?

[vintagekiki]

You have not overreacted, but you expect too much from the old man.
Can you record an audio clip with the amp on without a guitar, let's hear what's really going on.

[pamelahute]

It's absolutely clean with the new EZ81 and 2xEL84. Nothing noticeable.

[pamelahute]

here is a clean recording for you : https://www.dropbox.com/s/ops6ybrd76...aying.mp3?dl=0
Seems perfect to me.

[g1]

As I think there may have been a couple different issues, I'd appreciate if people would listen to the sound files and comment on those issues.
My comment was with regard to the first file in post #1, and post #6 at around 1m42s.
I have never heard a rectifier tube do anything like this and I would like to know if others have. To me it is the sound of a rattling power tube. A bad rectifier I expect to make glitching sounds like zzt etc., but I don't expect it to affect actual notes as it is not directly in the signal path.
I would like to hear about bad rectifier artifacts and which of the sound files you hear them in.

[Helmholtz]

here is a clean recording for you : https://www.dropbox.com/s/ops6ybrd76...aying.mp3?dl=0
Seems perfect to me.

Clip doesn't work for me: no sound.

[pamelahute]

As I think there may have been a couple different issues, I'd appreciate if people would listen to the sound files and comment on those issues.
My comment was with regard to the first file in post #1, and post #6 at around 1m42s.
I have never heard a rectifier tube do anything like this and I would like to know if others have. To me it is the sound of a rattling power tube. A bad rectifier I expect to make glitching sounds like zzt etc., but I don't expect it to affect actual notes as it is not directly in the signal path.
I would like to hear about bad rectifier artifacts and which of the sound files you hear them in.

Hello G&, thanks for your comment.
I think the 2 EL84 and the EZ81 were all problematic and changing them definitely fixed the whole thing, as you can hear on the two last sound clips.
Although I'm not a tech, I'm trying to think in a very simple way : Testing, changing and listening.

It's true that besides the resonance on certain notes, which was my main problem, the amp was making a weird hum sound when heating up. Again, it disappeared when the 3 tubes where changed.

- the amp made no weird hum nor resonnance when powered up - the issue appeared when it was warm - 3 min after powering approx. Which made me think it was not only the chassis.
- Hitting softly the tubes did nothing except with the EZ81 where I obviously could produce the same kind of resonnance I was trying to cancel
- Changing the EZ81 only did not fix the problem although the original tube was clearly defectuous
- Changing the EL84 pair as well as the EZ81 fixed everything : hum & microphonia

Hope this summary helps a bit,

I'll be happy to make more tests if needed.

Best,

Pam.

[pamelahute]

Clip doesn't work for me: no sound.

You have to put the volume up. It's the amp recorded without me playing to see the sound of the amp powered on, as vintagekiki requested.
It's perfect, the amp is super silent.

[vintagekiki]

here is a clean recording for you : https://www.dropbox.com/s/ops6ybrd76...aying.mp3?dl=0

Seems perfect to me.

FBT is absolutely silent, when you play (the previous clip) sounds solid.
All the audible sensations which you hear when the guitar is plugged in are normal because the PU detects all EM radiation in the room.

[pamelahute]

FBT is absolutely silent, when you play (the previous clip) sounds solid.
All the audible sensations which you hear when the guitar is plugged in are normal because the PU detects all EM radiation in the room.

Yes! It has never been so silent, almost hifi

[vintagekiki]

I'm glad that you are reanimate an old man.
He deserves to be gladden with new tubes.
Now take the guitar in your hands and