Model T making weird noises.



Model T making weird noises.

Postby conky » Tue Jul 05, 2016 8:01 am

I noticed a few days ago that my amp would hum pretty loud from time to time when we weren't playing. Sounds like 60 cycle hum. It never motorboats though, just a constant hum that comes and goes over the course of a few minutes. Then yesterday I was playing around and when I go around the 12th fret on the higher strings I hear a faint octave up. Tried swapping the stock 60's of for a new set of JJ KT88's and there wasn't that much of a difference. I did find one of my preamp tubes was microphonic though. Swapped it out and the hum isn't as bad but I still get the octave up. Tried it on different cabs and in different rooms and it's the same. It's time to get it recapped I imagine but I wanted to rule out any other potential causes.
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Re: Model T making weird noises.

Postby new05002 » Tue Jul 05, 2016 3:09 pm

conky wrote:I noticed a few days ago that my amp would hum pretty loud from time to time when we weren't playing. Sounds like 60 cycle hum. It never motorboats though, just a constant hum that comes and goes over the course of a few minutes. Then yesterday I was playing around and when I go around the 12th fret on the higher strings I hear a faint octave up. Tried swapping the stock 60's of for a new set of JJ KT88's and there wasn't that much of a difference. I did find one of my preamp tubes was microphonic though. Swapped it out and the hum isn't as bad but I still get the octave up. Tried it on different cabs and in different rooms and it's the same. It's time to get it recapped I imagine but I wanted to rule out any other potential causes.


That could be a failing cap in the supply chain increasing the amount of hum, could be a bad preamp tube as well. Sometimes if your guad of tubes is not well matched you might get some hum from a large mismatch. Dont forget that the Model T also has a hum balance pot on it that can be used to null out the heater noise, make sure that wasnt fucked with.
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Re: Model T making weird noises.

Postby conky » Tue Jul 05, 2016 8:09 pm

new05002 wrote:
conky wrote:I noticed a few days ago that my amp would hum pretty loud from time to time when we weren't playing. Sounds like 60 cycle hum. It never motorboats though, just a constant hum that comes and goes over the course of a few minutes. Then yesterday I was playing around and when I go around the 12th fret on the higher strings I hear a faint octave up. Tried swapping the stock 60's of for a new set of JJ KT88's and there wasn't that much of a difference. I did find one of my preamp tubes was microphonic though. Swapped it out and the hum isn't as bad but I still get the octave up. Tried it on different cabs and in different rooms and it's the same. It's time to get it recapped I imagine but I wanted to rule out any other potential causes.


That could be a failing cap in the supply chain increasing the amount of hum, could be a bad preamp tube as well. Sometimes if your guad of tubes is not well matched you might get some hum from a large mismatch. Dont forget that the Model T also has a hum balance pot on it that can be used to null out the heater noise, make sure that wasnt fucked with.


I swapped out all tubes to make sure it wasn't one of them and tried to original 6550s as well as newer kt88. First thing I did after tube swapping was check the hum balance pot. It was set correctly. I did notice that eh the hum started up if I tapped the big gold filter cap (I think that's what it is anyway) sticking up out of the chassis that the hum would stop. Taking it to a tech next week to get a check up.
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