Problem with Tube Head (Peavey)

[RockGuitarX]

My Peavey JSX has worked fine until last week. A preamp tube died so I replaced all the preamp tubes (yes they were the right ones) and lately if you tap the front panel or switch you can hear the glass sound of the tubes. If I turn the volume past level 2 I get horrible micro phonic feedback! Any ideas?!
Btw Hello everyone my name is Brett and I'm new here! Thanks.

 

[Wolfeman]

If I turn the volume past level 2 I get horrible micro phonic feedback! Any ideas?!

Answered your own question bud! Microphonic tube.

 

[AdamWathan]

Answered your own question bud! Microphonic tube.

Yup. Turn the amp on, open the back and tap on each tube with a pen or pencil or something similar. The culprit should squeal like a motherfucker.

 

[if6was9]

yeah sounds like a textbook bad pre amp tube issue. Sweet- always prefer these problems to the hard to trouble shoot ones. I just got an amp back after it being at the techs house for nearly 6 months!

 

[RockGuitarX]

Well I went to my local guitar store with the head and a lot of the techs were tapping it with a pencil claiming that it was a bad tube but when we replaced them it still didn't help... Maybe I need to get a whole new set!

 

[Metaltastic]

Yeah, preamp tubes are cheap enough as it is that you might as well, if nothing else cuz the new ones will be higher quality (as long as you get 'em from a good place, I'd go to www.dougstubes.com, great selection and great advice if you email 'em)

 

[RockGuitarX]

Hey thanks for the advice! I'll definitely consider that store cuz my local music store pretty much carries only groove tubes!

 

[Loren Littlejohn]

A total re tube is cheap if you know how to do it yourself. If not it's not even that much to have a tech do it. I had a head done at voodoo, new preamp and power tubes biased = $140. (voodoo and FJA are local for me.)

 

[RockGuitarX]

I wish I could bias power tubes

 

[Wolfeman]

I wish I could bias power tubes

Easy to do....
Do you have a multimeter?

 

[RockGuitarX]

No, but I would sure love to know where to find one? I have a bias test with a positive and negative outlet in the back.

 

[Metaltastic]

Eh, don't use those, there apparently really unreliable sources of info (at least on Peaveys). Check out this, click on video #5 ("Generic Bias using 800 Marshall"), watch it, and then scroll down to find your amp and see what the ideal mA is. Then go to the store on that website and buy a multimeter and a bias probe, and you should be good! (this, by the way, is how I went from your position to having my JSX going strong biased at 38 mA, so it should work for you!)

 

[RockGuitarX]

Hey thanks for that video! Bad ass

 

[beyond dead]

haha ya man thanks for the vid!

 

[Metaltastic]

No prob. dudes, glad to help!

 

[RockGuitarX]

I dropped my head off yesterday at the guitar shop for repair and got it back today. The problem is fixed! They said that the re-soldered the connections on the preamp board. Well thank you all for your help. I'm glad that's done.