Mesa Boogie Prodigy Microphonic power tube

[JKoehler]

Hoping to get some advice on my Prodigy. I've noticed recently that there was a glassy rattle coming from the back of the amp head mainly when playing an open E, and the E an octave above. After taking the top cover off, I carefully tapped the tubes with the pre-requisite wooden chopstick while the amp was on with the volume at around 12 o'clock. I noticed power tube V5 was the culprit of the rattle.
I could stop the rattle while playing an open E and lightly pressing down on the tube using a cloth to protect my finger from the heat.
I can't really tell if the rattle is coming through the speaker, or just the rattle is physically coming from the tube itself.
My question is, would using a silicone ring on the tube quell the rattle, or is this a sign of a tube going bad? The amp has a build date from 2014, and the current power tubes seem to be the original Mesa branded tubes. Thanks in advance.

 

[mikeswals]

Have you tried moving that tube to another socket? And have you isolated the head from cabinet with a foam pad or towel/blanket to see if the vibration stops?

 

[agedhorse]

Often the noise is mechanical in these power tubes. Tapping on them will make noise even with the amp powered off, hot or cold.

 

[JKoehler]

I noticed that when cold, the tube made the same rattle when tapped.
Would using the silicone tube dampers mitigate the rattle?

 

[agedhorse]

I noticed that when cold, the tube made the same rattle when tapped.
Would using the silicone tube dampers mitigate the rattle?

Probably not.

 

[nickelwound]

Was going to suggest getting a pair of new power tubes and get them replaced at you local tech. Holy mackerel, not sure if yours is the four or eight, but that's a lot of KT88's.

That's like $500 in power tubes.

 

[Wasnex]

I noticed that when cold, the tube made the same rattle when tapped.
Would using the silicone tube dampers mitigate the rattle?

Could it be the clamp that holds the tube in place?

 

[Sparky Mark]

Could it be the clamp that holds the tube in place?

I'm not convinced tube retainers are needed at all, other than when transporting an amp.
I also think the spring type retainers have potential to scratch the glass which can cause tube failure. If my tube amp was permanently studio based I'd remove the retainers (assuming the tubes are pointing upwards that is).

 

[rodl2005]

So if you're having to replace a power tube, what are your options?

 

[mikeswals]

Was going to suggest getting a pair of new power tubes and get them replaced at you local tech. Holy mackerel, not sure if yours is the four or eight, but that's a lot of KT88's.

That's like $500 in power tubes.

His is a 4-tube unit.
I've been using Eurotubes for JJ's for over 20 years now, and a Quad is $256. He also does stringent testing and qc.

The Prodigy has on-board bias lights and adjustment pot, so new tube set up is very DIY and easy.

 

[nickelwound]

His is a 4-tube unit.
I've been using Eurotubes for JJ's for over 20 years now, and a Quad is $256. He also does stringent testing and qc.

The Prodigy has on-board bias lights and adjustment pot, so new tube set up is very DIY and easy.

I tried to find a manual to see if it had the bias adjust,couldn't find one quickly. That's how I found out about the 4 and 8.

Eurotubes is what I would have suggested as well. Power tubes seem to rattle after awhile no matter what. At least for the guitar amps and tubes I've had.

 

[Wasnex]

I tried to find a manual to see if it had the bias adjust,couldn't find one quickly. That's how I found out about the 4 and 8.

Eurotubes is what I would have suggested as well. Power tubes seem to rattle after awhile no matter what. At least for the guitar amps and tubes I've had.

Prodigy Manual is here: https://mesa-boogie.imgix.net/media/User Manuals/bassProdigy_170612-web.pdf

Bias discussion starts on page labeled 21. It's page 26 of the document. Procedure for non-techs starts on the page labeled 22.

 

[Sparky Mark]

I could stop the rattle while playing an open E and lightly pressing down on the tube using a cloth to protect my finger from the heat.

Doesn't this indicate the rattle isn't coming from the tube's internal structure?
Have you removed the tube from the amp to tap and shake it in isolation?

 

[JKoehler]

I took the tube out of the socket, and after tapping it, it does indeed make a rattling noise. The power tubes in a Prodigy have tube clamps much like an SVT, so there's nothing rattling on the glass portion of the tube.
I did notice also that there seemed to be something shifting internally, ever so slightly, when tapped that the other tubes didn't have when tapped in the same manner.
I'm guessing this tube is bad, but the sound of the amp is great, and really loud. Can a tube with this condition be considered "bad", or will it still function, just with the "glassy rattle"? I've owned/played tube amps for well over 35 years, and know when it's time to take it to an amp tech, but never had a tube do this. Where everything sounds fine, except for this audible noise coming from the tube itself. Thanks again for all the input.

 

[Sparky Mark]

I took the tube out of the socket, and after tapping it, it does indeed make a rattling noise. The power tubes in a Prodigy have tube clamps much like an SVT, so there's nothing rattling on the glass portion of the tube.
I did notice also that there seemed to be something shifting internally, ever so slightly, when tapped that the other tubes didn't have when tapped in the same manner.
I'm guessing this tube is bad, but the sound of the amp is great, and really loud. Can a tube with this condition be considered "bad", or will it still function, just with the "glassy rattle"? I've owned/played tube amps for well over 35 years, and know when it's time to take it to an amp tech, but never had a tube do this. Where everything sounds fine, except for this audible noise coming from the tube itself. Thanks again for all the input.

If a component has become detached within the tube, I don't think there's a way of reattaching it. Depending on which component it is, I guess it could fail at any time in many ways. It seems a pity to bin an expensive "working" tube, but for peace of mind, that seems the most sensible thing to do.

 

[agedhorse]

I took the tube out of the socket, and after tapping it, it does indeed make a rattling noise. The power tubes in a Prodigy have tube clamps much like an SVT, so there's nothing rattling on the glass portion of the tube.
I did notice also that there seemed to be something shifting internally, ever so slightly, when tapped that the other tubes didn't have when tapped in the same manner.
I'm guessing this tube is bad, but the sound of the amp is great, and really loud. Can a tube with this condition be considered "bad", or will it still function, just with the "glassy rattle"? I've owned/played tube amps for well over 35 years, and know when it's time to take it to an amp tech, but never had a tube do this. Where everything sounds fine, except for this audible noise coming from the tube itself. Thanks again for all the input.

It may in fact function fine for years that way. If you don't find if too objectionable, keep using it.

It may be just one of the mics spacer fingers not fully in contact with the glass.

 

[JKoehler]

Okay, that brings me back to tube dampers. I don't buy in to all the hype on how they improve the sound characteristics of the tube. I'm wondering if I were to try them in reducing rattle noise, is there any chance in damaging the tube from heat buildup, or anything like that?

 

[agedhorse]

Okay, that brings me back to tube dampers. I don't buy in to all the hype on how they improve the sound characteristics of the tube. I'm wondering if I were to try them in reducing rattle noise, is there any chance in damaging the tube from heat buildup, or anything like that?

Probably not going to damage anything by trying them, but they may no help either.