Hi Everyone,
Well, I just finished by 67 plexi build and I loaded her with a quad of 6550's. The amp is great - headroom, tone, and the overall loudness will wake the dead. With that said, I have a 69 marshall major PA (8 input) sitting underneath the 67 plexi. I played both last night and to my surprise the 67 plexi was a helluva lot louder! The major has a quad of valve art kt88 in it with a master volume ( I am getting ready to take the MV out ) because I think there is something wrong there; it has a scratchy pot and noisey. The amp was recently serviced and the tech said it looked fine.
I just find it hard to believe that the major is quieter than the 67 plexi. I had the major up to 10 in my room with no problem, but the tone was clean as a whistle - no breakup whatsoever.
Sorry for the long post. Any ideas?
Thanks for looking
plexi and major
Moderators: pompeiisneaks, Colossal
Re: plexi and major
Sounds like there is a bad resistor or pot somewhere in the preamp. Surprised the tech didn't catch that. Could also be a bad connection somewhere. In any case, sounds like something isn't passing signal as it should. Does it do the same thing on both channels? On 10 it should be quite overdriven and shaking the house apart.
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Stevem
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Re: plexi and major
No distortion from the Major means not enough drive to the output stage more than likely!
I worked on guys Major once and he has swapped out the 12au7 PI tube for a ax7 and you can not do that in a Major, even though the ax7 was good the amp barly made 92 watts of rms power and since these amps are designed to be clean, naturally the output stage would not overdrive with that tube in there!
Even if the Major was working 100 % do not expect twice the volume over the plexi, all you will have is near twice the clean head room before the output stage clips!
I worked on guys Major once and he has swapped out the 12au7 PI tube for a ax7 and you can not do that in a Major, even though the ax7 was good the amp barly made 92 watts of rms power and since these amps are designed to be clean, naturally the output stage would not overdrive with that tube in there!
Even if the Major was working 100 % do not expect twice the volume over the plexi, all you will have is near twice the clean head room before the output stage clips!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: plexi and major
Thanks guys. The MV is coming out....not by me though! I will check the pi tube.
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Reeltarded
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Re: plexi and major
It should be disassembling your cabinet.
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
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JazzGuitarGimp
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Re: plexi and major
Is it possible one or more of the preamp tubes has been repaced with 12AY7 or 12AU7?
Lou Rossi Designs
Printed Circuit Design & Layout,
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Printed Circuit Design & Layout,
and Schematic Capture
Re: plexi and major
All preamp tubes are 12ax7. In addition, I also played through all 8 inputs and there is a big difference. Inputs 1 and 2 are much much quieter than input 3 and 4. I guess I will need to take it to the tech again. The MV really sucks and it's so noisey.
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Reeltarded
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Re: plexi and major
The PI is also a 12ax7?
These are the only Marshall that I love with the PPIMV. while he is in there have him cut the NFB. It's WAY better without it.
Where are you in SC? I am in Savannah.
These are the only Marshall that I love with the PPIMV. while he is in there have him cut the NFB. It's WAY better without it.
Where are you in SC? I am in Savannah.
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
Re: plexi and major
Have you tried swapping the preamp tubes around? Namely the left two tubes when looking at the back should be the first stages for channels 1,2 and 3,4. Or try new ones?
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Stevem
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- Joined: Fri Jan 24, 2014 3:01 pm
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Re: plexi and major
Well that's the amps main issue than, no 12au7 in the PI location!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: plexi and major
So, I need to change the PI to a 12au7? I will double-check again.
The 12ax7 cannot supply enough power to the power tubes??
I am in the Greenville/ Spartanburg area.
The 12ax7 cannot supply enough power to the power tubes??
I am in the Greenville/ Spartanburg area.
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Reeltarded
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- Joined: Sat Feb 14, 2009 4:38 am
- Location: GA USA
Re: plexi and major
AU7 in PI. it's about the current, yes.
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
Re: plexi and major
Well, there was a 12au7 tube in the preamp section, but it was in V2. I swapped it for the tube in v4 and the volume is definitely louder and is equivalent to inputs 3 and 4 now. It still funny, because it does not get super loud until it is nearly cranked, but I suppose that has to do with the volume pot taper.
Thanks for the help guys!
Thanks for the help guys!