help !!! guitar amp feedback

[Zeppelin4Life]

yes. I know for a fact its(or could be) the preamp tubes, I had the exact problem. try moving them around (swapping the tubes for each others spot..except the phase one). that was a good temp-fix for a few weeks, then they finally died. (fuzz, hiss, buzzing, weird harmonics).

www.eurotubes.com
www.firebottle.com
www.newtube.com
www.worldtubeaudio.com

[soundguy]

buy new tubes and put them in and be done with this.

if you tap on a preamp tube and you hear the tappng through your speaker this is hardly a sign that the tube is bad. Also, a worn out tube is not going to LOOK bad compared to one that is good. Also, tubes do not typically die in a linear fashion, becaue it was squaling one night doesnt mean it will happen the next. Also, guitars dont all have the same output, so one guitar can push a tube harder than the next if the problem is with the preamp tube and not the phase inverter. Also, the internet is for porn.

dave

[Zeppelin4Life]

Also, the internet is for porn.

meat curtains.

[Knights Who Say Neve]

buy new tubes and put them in and be done with this.

if you tap on a preamp tube and you hear the tappng through your speaker this is hardly a sign that the tube is bad.

I wasn't clear in my original post. What I meant was- if you tap the preamp tubes, and one make a lot more noise (esp. a "ringing" noise) than the others, that's the bad one.

That having been said, you really ought to replace all of them. At the worst, you'll have some spares. You can also look at it as a wonderful opportunity to enter the voodoo world of tube substitution for better tone

[doozerface]

zepplin4life referred to not moving the phase tube. Which one is that? Im going to do the tapping test asap. If one of them buzzes and i need a new tube do i have to worry about biasing or anything like that?

thanx ya'll

[Knights Who Say Neve]

The phase tube is the one nearest the output tubes. (In Fenders anyway...is it different in any amp you know of? Anybody?)

You don't have to bias preamp tubes. No worries there.

BUT, if you find one bad one, replace them all! They're likely to all be the same age, and they're only 10.00 apiece or so...

[SKEETER]

I think soundguy is likely right, and that the reason it does it with the SG is that the SG pickups are more microphonic than other guitars you tried. If the tubes are singing, I am thinking they probably generate a pitch that the SG pickups are regenerating.

[vvv]

The phase tube is the one nearest the output tubes. (In Fenders anyway...is it different in any amp you know of? Anybody?)

On Marshall 800's the phase inverter is typically the farthest, in the right front corner, and all by it's lonesome. Well, it is on my Silver Jubee's.

[Antero]

It could also be your pickups gone microphonic (boy, tons of things gone microphonic around here!) - if they're not potted, and you're at a high volume, the coils vibrate...

[Zeppelin4Life]

The phase tube is the one nearest the output tubes. (In Fenders anyway...is it different in any amp you know of? Anybody?)

On Marshall 800's the phase inverter is typically the farthest, in the right front corner, and all by it's lonesome. Well, it is on my Silver Jubee's.

that's weird. most of the phase -/+ tubes are closest to the power tubes.


at least I know its like that on peavey, fender, and Ithought marshall

[doozerface]

So I am really worried about screwing something up but my plan is:
sovetek 12ax7lps in the first and second position and a ruby 12ax7a in the third/phase position. That will work out fine right? by work out i mean make the amp work correctly.

[Huntlabs]

Different preamp tubes can drastically change your amps sound.

I tried the LPS Sovetecs and didn't like them. I'd reccomend some WA. I've also started to like Electro Harmonix Tubes. Might try them out. Seems like Sovetecs are kinda crapps sometimes.

Do some research and if you can't figure it out post away! I'm happy to help

The first link discusses your problem:

http://www.rivera.com/Rivera/details/tubes.shtml
http://www.thetubestore.com/index.html
http://www.sovtek.com/
http://www.magicparts.com/new/default.htm

John

[doozerface]

Im not so much hearing the ringing in the tubes when i tap them with the pencil but i figure it cant hurt to replace them all. My amp has 3 12ax7lps in it now, im pretty into the sound so i was just going to replace those. Im going to try the ruby in the phase position because that was recommended to me. I've never tried anything else enough to really have a position on how others would sound. Does a specific tube in the phase position do anything different of special?

i've also read the 12ax7wb's sound good in marhshalls? Are there pros and cons to mixing and matching preamp tubes?

[stooge]

No real problems with mixing and matching preamp tubes.

12AX7s, 12AY7s, and 12AT7s all pin out identically and can be interchanged with no problems.

Likewise, you can mix and match preamp tubes to your heart's content with no ill effects...but different brands will change the tone of your amp, the quality and amount of overdrive, available clean headroom, etc.

In a nutshell, 12AT7s have a lower amplification factor than 12AX7s. This means that if you put them in the preamp stages, they will tend to be cleaner. They also tend to be quieter overall. I would recommend keeping a 12AT7 in the driver position though, because sometimes a 12AX7 will make things...well, a little hinky.

...Soooooo, to answer your question, if you feel like mixing and matching, knock yourself out. You're not gonna hurt anything by doing it. If you don't like the results, swap the order of 'em. If you don't like that, swap 'em out for something else. At about $10 a tube, it's not too bad.

One small hint...if you're running your head directly on top of your cab, and especially if you're cranking it up on a regular basis, you might want to check the feet on the bottom of the head. Some Marshalls used plastic feet as opposed to soft rubber...and if you play it cranked the vibration from the cabinet transfers up into the head. I have a Bassman head that went through a full set of preamp tubes every 6 months like clockwork, and I couldn't figure out what was going on until I realized the "rubber" feet on the bottom of the head had hardened and the cab was basically shaking the preamp tubes to death. I went to the hardware store, bought a set of 3/4" big soft rubber feet, and replaced them.

I've been using the same preamp tubes for the last 2 1/2 years with no problems whatsoever.

[chris harris]

does your sg make the same squealing sound when you plug it into your friend's Fender amp and really crank it? how about with a distortion pedal on?

microphonic pickups are another cause of this kind of problem.