question for the amp gurus about microphonic tubes

[Riggins]

I am having an issue with a preamp tube and was wondering if someone would know this.

 

I did the tap test and found the 12at7 in V1 was microphonic, so I bought a new one and replaced it, only to find it is microphonic as well.

The question is; can there be something in the circuit, parts on the board, or even the socket that can make a tube microphonic besides the tube itself?

 

Just wondering if I need to take it in for repair or maybe I'm just unlucky and bought a new tube that happened to be microphonic as well.

 

I have other 12ax7's that I will try tonight but I thought it unlikely that the new one I bought would be bad as well.

 

Any thoughts or help on this would be greatly appreciated!

[Mustaine-who?]

Try putting one of your other 12AX7's (one that you know is good) into the slot you suspect is bad. What happens? Did the microphonic thing just start happening? Why do you have a 12AT7 in V1?

[NaturalBornBoy]

 

I am having an issue with a preamp tube and was wondering if someone would know this. I did the tap test and found the 12at7 in V1 was microphonic, so I bought a new one and replaced it, only to find it is microphonic as well. The question is; can there be something in the circuit, parts on the board, or even the socket that can make a tube microphonic besides the tube itself? Just wondering if I need to take it in for repair or maybe I'm just unlucky and bought a new tube that happened to be microphonic as well. I have other 12ax7's that I will try tonight but I thought it unlikely that the new one I bought would be bad as well. Any thoughts or help on this would be greatly appreciated!

 

 

Just try swapping your other tubes that you know to be in perfect working order in the V1 slot. If they go microphonic immediately then something else may be wrong

[newholland]

yeah-- sometimes the solder joints can go squirrely and make similar rattling noises-- but there ARE a lot of microphonic tubes floating around! try another still.. or any others around you KNOW are good. if the rattly one is bad in other positions-- you know it's a bunk tube.

[Cougar Hunter]

 

there ARE a lot of microphonic tubes floating around!

 

 

+1.

[Riggins]

 

Why do you have a 12AT7 in V1?

 

Smooths out the VK100H big time. With a 12ax7 in that spot it's very fizzy sounding.

 

 

yeah-- sometimes the solder joints can go squirrely and make similar rattling noises-- but there ARE a lot of microphonic tubes floating around! try another still.. or any others around you KNOW are good. if the rattly one is bad in other positions-- you know it's a bunk tube.

 

 

That's what I was wondering. I have quite a few 12ax7's floating around that I know are fine. I guess I'll give them a shot and see what happens. I just wanted to be sure that either there was absolutely no way it could be anything but a tube or that there are circuit issues that can also cause it.

 

Thanks a bunch guys. Much appreciated!

[WRGKMC]

There are known brands of tubes that are microphonic in one application that may not be in another. If you go the some tube wholesaler like Tubes and More and read up on their reviews you will probibly find the best match for your application.