Mark III sounding pretty bad

[Subby32]

So I've got my Mark III Fully Loaded Blue Stripe retubed with a brand new set of Tung Sol Pre Amp Tubes. They sound pretty nice and lively but the amp has a nasty harsh buzzing no matter what the settings even with treble/presence/high eq all on zero.

The clean channel sounds beautiful and the rhythm aint too bad either, and I remember only a few months ago the amp was able to get really dark and smooth but not anymore.

Could power tubes cause this harshness or is it something more serious like needing a cap job?? It is from '88 i think so Im sure it can use a tune up.

Does this harshness just sound like power tubes or something else?? Also Im running through a vintage Orange 4x12 which is really warm.
Thanks
Chris

 

[rippingrudy]

Could need a cap job. Or, could be old power tubes but I doubt it... Or could just be you don't like the fizzy/buzzy gain on the Mark III. I sold mine because of that.

 

[user 2126]

Or could just be you don't like the fizzy/buzzy gain on the Mark III. I sold mine because of that.

Hey Subby32 forget that quote, your Mark III is not suppose to sound like this dude said unless you got some problem with it, some dude here don't know how to tweek this beautifull amp. Don't forget your III is powerfull and can really sound sweet.
Try my setting ounce your problem is resolve.

 

[user 2126]

Humbucker pups my friend.

 

[timv]

Is the buzzing in all channels or just the lead? You said clean sounds good and rhythm also. If they sound good without any buzzing then try swapping the preamp tubes around or swap them one at a time. It may just be the lead 12AX7 is bad.

 

[Buddy]

Could be , with the new tubes , you are hearing more , the old pots might be showing their age . Is it a combo ?
Play it and move the knobs . Does the noise kick in /out ?
Saw this with my '87 rs . Replaced a few pots , Happy day's !

B.

 

[Subby32]

The amp used to sound amazing I would always get tons of compliments at shows and I never set it for a metal sound, just a nice thick warm kinda high gain tone and it was perfect.

Now the amp has a really harsh grating quality like there is buzzyness attatched to any note i play. I know how to dial it in really well thats not a problem.

Also the amp hums and has a good amount of background noise which i dont remember it ever having....and ive switched in a few different pre's in all the slots and i know thats not the problem.

Anyway to check if the caps are bad? And how can I clean the pots because i had an intermittent problem of the master volume being on zero yet it would be loud, and sound scratchy as i turned it up.

 

[PHYX]

If it only happens on your lead channel it could be your vol. pot for that channel. My Mark IV had that problem on my master output vol pot.
Jim

 

[Shep]

have ago at swapping V1 for a JJ preamp tube..it's darker..have a go at cleaning all the tube sockects..?

 

[Schmoog]

what kind of tubes were you running in it before you retubed it? did it have tung sol's before?

 

[Subby32]

uh pres were EH and a mesa 12ax7 in V1, but even with those in there it sounded rough, thats why I changed them.

Today Im gonna take the chasis out, go through all the pots and tube sockets and make sure everything is clean
Thanks for the replies

 

[Anonymous]

That's funny, I've been having some problems with my Mark III recently as well. Except my problem is I can't get any treble out of it. :?

 

[Schmoog]

the EH's have somewhat muted highs. I used to use them in my peavey classic 50 to calm down the preamp brightness. so the tung-sol's might be brighter and your now noticing the brightness of the amp that you didn't before

 

[Subby32]

Well I just got new power tubes.
6l6 and el34 SED Winged C's and up loud the amp still sounds soo harsh.

Can it be a fried resistor, caps, pots?
Im out of ideas on what I can look at myself and dont have a good tech I know of in CT.
Also would like to diagnose on my own if I could.

Worse comes to worse I guess i can send it out to mike b for the r2 mod, reverb mod, triode/pentone, c+ mod, and an overall checkup...
but its gonna take awhile for me to get together that kind of money and I would like the amp working now.

Any other ideas?
Thanks

 

[murray]

Hello there - had a similar problem with my mark 11c , it was a cracked circuit track around the power tubes , have a look at your boards with a magnifiying glass , could also be a resistor or a capacitor , but you'll have to lift one side of these components to check with a capacitance tester , only about $15 on the net or a ohm meter . or you can check the voltages , one probe to ground , other probe to the component you want to test , but watch you don't get a shock , more than likely the problem could be on the board that the power tubes are on , or the power supply board check the large capacitors , or change them one at a time with new ones , hope this helps , it took me a few day's to find my problem , regards Murray.

 

[Subby32]

Thanks murray,
that sounds like it could be a possibility
ive got new F&T and sprague filter caps coming this week, but i got a magnifying glass and want to inspect the board
Can you specifify which board the power tubes are on? I dont see mine being on one...
How obvious is a cracked circuit track?
Thanks

 

[murray]

On the mark 11c the valve sockets are soldered right to the board , you can actually see the valve pins , there the big valves 6L6's , the crack in my board was difficult to see , i went over the board with a plastic knitting needle ( power off ) and pushed down on the circuit tracks while looking through the magnifying glass , if you have a crack in the track you will see it move when you push on it , if you find a crack just clean the track and put a dob of solder on it to bridge the broken track, i just forget which part of the circuit was faulty on my amp , but it was on one of the tracks that fed a 6L6 valve so only one valve was working , and the amp sounded shocking , if you percever you will find the problem , good luck regards Murray.

 

[Buddy]

Mark III power tubes are mounted right in the chassis .

 

[murray]

different to a mark 11 - it's hard wired straight to the components - can you take a pic of the whole works regards Murray. :shock:

 

[Buddy]

Sure , here ya go .
click thumb .