i've noticed that my amp is very... hissy sounding... i cant really kill the fizz that comes out overtop of my tone, and when i roll back the trebel or the presence, it kinda fixes it, but at the same time completely reduces everything to mud.
Ontop of this, its very very very warm sounding, and i'd like to cut back on it without butchering the tone.

Would retubing it fix the problem? Right now its loaded with original preamp tubes (14 years old, ouch), and some poopy sovtek/mesa boogie 6l6's.

The 6l6's are new, but would changing them to el34's help my prediciment?

And can my marshall even be rebiased to accept el34's? I cant find bias points anywhere on this thing, and i'm looking up its ass and can see its adam's apple.

thanks.

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Old preamp amp tubes are the biggest cause of microphonics. Given that they are 14 years old, I can almost guarantee that swapping them out would help a shit load.

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its not constant hissing though... like the amp is silent when i dont play. When i do play theres like a super trebly undertone or something. Would that still be considered microphonics?

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It could be, look at it this way. All preamp tubes are microphonic, its just a matter when that microphony occurs, a threshold if you will. Tubes that are quiet have a high threshold, meaning that their day to day use dosent exceed that threshold. It sounds like your preamp tubes could possibly be on the edge, and when you put a strong signal to them, they become microphonic. However, sadly, some preamps are voiced to have those super trebly overtones, and the only way to remedy that is have the voicing of the preamp altered.

Either way, 14 year old preamp tubes should be out faster than Michael J. Fox in a game of Jenga.

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Fuckin sigged.

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You say "super trebly undertone" i immediately think of the frequency range 4.5KHz-8KHz. Now an important thing to understand is that most modern high-gain amp makers today design their amp to totally kill just about anything above 5.5KHz (number may vary from everything to 3.5-7KHz) (higher frequency is a higher pitch). There are a couple of reasons for this, among those is the one that almost no 12" guitar speakers have a usable frequency response above 5.5KHz, making the signals you send to it that are above 5.5KHz seem like it's in the background of your playing creating an annoying undertone-effect (grainy/harsh decay just about everywhere), plus frequencies above 5.5KHz on a guitar are pretty much harmonics that do not sound very good to the human ear. Now amp makers realize that some people might want some of the stuff above or around the magic 5.5KHz mark so they install small circuits between the gain stages of the amp and in the power section that kill off some of the high end to a varying degree, so that it's tuned to sound pretty strong up to around 4-4.2KHz (this is called "great attack"), but from there onward reducing the signal strength considerably. But, there's a magic button, also called the presence control (which is a control that (simplified) boosts high frequencies in the power amp). With it, players can decide how much of the stuff around 4-7KHz they want to put back INTO their signal and into their speakers, sort of setting the cut point themselves.

Anyway that was a huge rant but it may educate someone so i guess it's somewhat useful

Anyway, my advice in your case:
Old (and new) Sovtek preamp tubes have a very well-known reputation for sucking large amounts of ass with their very harsh and piercing highs combined with low gain and fizzy overdrive. Even changing to new Sovteks would in your case be a huge improvement (things have improved a lot in those 14 years), but for your case I'd change to a tube with a little darker character and a little "meatier" overdrive (not so "fizzy", more "angry growl"). Anyway I'd try JJ 12ax7's for the preamp and phase inverter (tube closest to power tubes). If it sounds a little dark now try replacing one of the JJ's with a tube from the "Sovtek" factory, namely the Electro-Harmonix 12ax7 which is a little brighter with a fizzier overdrive but still with good harmonics and great bottom end. Also take into consideration that tubes all have a similar sound on the high-quality side, the differences are very subtle.

BTW what amp do you have? JCM900? If it has a presence control: The point with the treble and presence control is that you adjust back and forth in intervals till you've gotten rid of the nasty "fizz" but haven't totally killed the top end and clarity. Remember that your ears may get tired out, so take regular breaks during this adjustment session where you turn it all off and relax your ears for a minute (read a book or something), this will keep them reliable (not cool spending an hour on adjusting, then next day when you're gonna practice it sounds like shit). Take a break every time you feel you've dialed out something you really wanted in your top end, "reset" your ears and re-listen.. huge difference.

In regards to Sovtek preamp tubes, you really need to pick the right ones. I once had an interesting experience with an old amp involving Sovtek tubes. I was returning the amp so I took my good preamp tubes out and put the old ones (a pair of Sovtek 12AX7-WB's) back in. The next day I went to play it a bit before I was to take it back and had completely forgotten about putting the old tubes back in. About every minute or so I kept looking down to check my Wah pedal because my distortion had a slight bit of that "wah pedal half way down" sound to it. But everytime I looked it was all the way back. That was when I realized that I had in fact put the old tubes back in, and that they were so nasally and weak that they sounded like a half-cocked wah pedal.

So long story short:

-Sovtek 12AX7 WA or WB, NO
-Sovtek 12AX7-LPS, YES.

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The LPS is okay, i find the sound character a little boring and flat, but it may be just right for some setups. EH, reissue Mullard & Tung-Sol are also sovteks BTW.

Yup, a lot of what Mesa puts in their amps is Sovtek as well. Im not a fan of most of their stuff, I disliked the Tung-Sol reissue 5881's (btw xdislexicx if you read this, the Powerball wasnt designed to use 5881's, far too weak, a good set of SED 6L6GC's lit that amp up!)

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Yep, the SED =C='s are by far the best bet for brutal chugga-chugg DM

Are Sovtek 12AX7-LPS's even made anymore? Def said he got em to sound real good in his Engl 620 preamp. But I couldn't find em at Thomann.de

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If you're in Europe, Soeru, http://www.tubetown.de/ttstore/prod...-ECC83-LPS.html

I would try JJ's before, they tame some of the unwanted fizz

Cool which would you consider best for an Engl pre? JJ's? I figured that was what I was gonna get but I was wondering if there were a little better ones for rich full sounding high gain stuff with a good lowend but still tight.

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Everyone loves JJ's in engl amps.

amp: marshall 6100 (30th anniversary head) (could be built anywhere in '93 or '94)
tubes: 6 original "marshall" preamp tubes, 1 original "marshall" phase inverter. 3 mesa boogie 6l6's 1 sovtek 6l6 (i looked closely at the mesa's and sovtek and it turns out theyre identical, just different label.

I do have a presence control, but i'm having trouble getting the fizz out with it because i tend to lose dynamics when i do.
Oh, and about the high kHz overtones, i could probably blame some of it on my heap of shit spider II cabinet... which is built to compliment the spider which is super dark.
but yeah, seems its time to spend a load of money on 7 preamp tubes hahahah. Oh, does anybody know where i can get a preamp tube shield? my phase inverter slot is missing one and is just bare... it looks so sad and naked

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Those original marshall's are Chinese ones, they have a pretty grainy/buzzy overdrive (IMHO terrible). Replacing those will help your tone by the thousands ;-)

um... so i was reading around, and i noticed Valtiel made a comment about 5881's and 6l6's being different... well my amp has a 5881 plastered right on the front... so would that help my tone and get me higher levels of gain?

oh, and if it would be a good thing to go over to 5881's, does anybody know some good ones?

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5881's are the European counterpart of 6L6's, much like ECC83's are to 12AX7's.

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That is what I addressed in that other post, they are NOT the same. 5881's, apart from being noticeably smaller in actual size, they are completely different tonally and have less power. Do not swap them back and forth as though they are the same.

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this is exactly what i have
http://www.thetubestore.com/sovtek5881.html
turns out they were 5881's after all.

So what would happen to my gain/tone/overall if i popped them out and threw in some winged c's (i'm lookin at you Val )

i dont know if i've asked this before, but, can this amp even be rebiased? i cant find bias points ANYWHERE.

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5881 = smoother (rounder) tone than 6L6's

The SED's just generally overall kickass. Very deep, tight bass, smooth growly mids, screaming highs.. Very good detail.

That was fucking ace man! Good shit

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