#1
The other day when I was practising with my band, my amp started to act wierd... when I turn the master volume past 5 it starts whistling very loud when a string is not ringing. Kinda like feedback, but this is something else. This only happen when the amp is overdriven. I discoverd that if I turn down either the tone or the volume knob on the guitar a bit it goes away... Ive heard that when preamp tubes starts to wear out, it can be noticed like this, but my amp sounds nice when master volume is below 5, and on clean, so I dont have a clue ! its an old amp though - 1983..

Anyone know whats wrong ?
Gibson Les Paul Standard
Takamine G Series 6&12 string accoustics

Marshall JCM 800 50w 1987 (4 input)
Marshall 1936 Cab

Jim Dunlop CryBaby
MXR 10 band EQ

R n'fn' R!
#2
new tubes
you need to beable to push that tube amp to atleast 5 to get that nice tube sound.
#3
I just replaced the powertubes
Gibson Les Paul Standard
Takamine G Series 6&12 string accoustics

Marshall JCM 800 50w 1987 (4 input)
Marshall 1936 Cab

Jim Dunlop CryBaby
MXR 10 band EQ

R n'fn' R!
#5
how could a bad cab cause that kind of sound ? and why does it go away when I roll down the volume or the tone knob on my guitar ? I just have to roll them down to like 7 or 8, not all the way down
Gibson Les Paul Standard
Takamine G Series 6&12 string accoustics

Marshall JCM 800 50w 1987 (4 input)
Marshall 1936 Cab

Jim Dunlop CryBaby
MXR 10 band EQ

R n'fn' R!
#6
You talked to me over MSN, could be the MG cab doesnt stand up to it!
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Last edited by Gabel at Aug 20, 2006,
#7
I discoverd another thing, the whistling only appears on the hi gain input, not in the normal input....
Gibson Les Paul Standard
Takamine G Series 6&12 string accoustics

Marshall JCM 800 50w 1987 (4 input)
Marshall 1936 Cab

Jim Dunlop CryBaby
MXR 10 band EQ

R n'fn' R!
#8
could be a preamp tube going microphonic or something, especially if it's only happening on the high sensitivity. Maybe you can narrow it down to a specific tube, since it's not happening on both inputs. It won't be the driver, since that is the end of the chain, and it won't be the first input tube I don't believe, since I think it would be happening on either inputs if that were the case. Do you have any spare preamp tubes you can swap in?
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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Last edited by Erock503 at Aug 21, 2006,
#9
nope..

But I think your on to something

Could I try moving the preamp tubes around ?
Gibson Les Paul Standard
Takamine G Series 6&12 string accoustics

Marshall JCM 800 50w 1987 (4 input)
Marshall 1936 Cab

Jim Dunlop CryBaby
MXR 10 band EQ

R n'fn' R!
#11
Quote by Sl4Sh_Jr.
nope..

But I think your on to something

Could I try moving the preamp tubes around ?

yeah, you could try switching around the inside tubes, just to see if you could get it stop on the high senstivity. But, like Gabe said, new tubes would be best. Preamp tubes are pretty cheap, and then you can play around with different preamp tube options. I've found that different brands can give less/more gain, smoother/rattier, etc..
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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#12
I think im going to buy some new tubes...
Gibson Les Paul Standard
Takamine G Series 6&12 string accoustics

Marshall JCM 800 50w 1987 (4 input)
Marshall 1936 Cab

Jim Dunlop CryBaby
MXR 10 band EQ

R n'fn' R!
#13
probably a good idea anyway. It's always a good idea to keep a spare too. My Mark IV has 2 spare preamp tube holders behind the grill cloth. With preamp tubes, since you don't have to bias them, and they last a lot longer than power tubes, I've found a lot of times they don't get changed for many years.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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#14
i bought it used so I actually dont know how long its been since they were changed last time...
Gibson Les Paul Standard
Takamine G Series 6&12 string accoustics

Marshall JCM 800 50w 1987 (4 input)
Marshall 1936 Cab

Jim Dunlop CryBaby
MXR 10 band EQ

R n'fn' R!
#15
If they are really old, you could notice a very nice increase in tone and gain. My Mark IV had very old preamp tubes when I got it, and sounded pretty lifeless. After new preamp and power tubes, it sounded like a completely different amp.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
amp clips
amp vids