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- May 24, 2019
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My reverb quit working so I pulled the chassis and isolated the reverb tranny as the problem. Ordered one from Mesa.
I changed the 3 filter caps, 470uF16v and 270uF63v caps some years ago. I also added Don's lead drive mod and moved the reverb to the back.
The amp works great but I don't use it much these days. It is noisy.
I was checking resistor values for my amp wondering why it had turned the board black above the EL84 power tubes.
It was like that when I got it off Ebay. I put a fan in the bottom of the cab to cool it some.
People say they run hot but why is that?
.
Here is what I got around the power section. I have the readily available schematics from the internet.
R201 and 202 read 1.5M instead of 2.2M.
R222 and 224 read 295K instead of 330K.
These feed the EL84 pin 2 control grids.
These are in the feedback loop.
R207 reads 1.465K which is close to 1.5K on the schematic.
R252 reads 1.466K instead of 56K on the schematic. This is the big outlier. Could this be a problem?
R207 and 252 are in series on either side and intersect the line from the Presence pot to the V5B pin 7 grid.
Can I change something somewhere to make the amp run a little cooler without messing up the sound?
Also the amp is noisy and they say it is caused by the C6 47pF cap and R104 3.3M in parallel at the input to the grid of V2A which is the first stage of the clean channel.
Can this be modified to quiet the amp down? Is there anything else that would help?
Thanks for any response.
I changed the 3 filter caps, 470uF16v and 270uF63v caps some years ago. I also added Don's lead drive mod and moved the reverb to the back.
The amp works great but I don't use it much these days. It is noisy.
I was checking resistor values for my amp wondering why it had turned the board black above the EL84 power tubes.
It was like that when I got it off Ebay. I put a fan in the bottom of the cab to cool it some.
People say they run hot but why is that?
.
Here is what I got around the power section. I have the readily available schematics from the internet.
R201 and 202 read 1.5M instead of 2.2M.
R222 and 224 read 295K instead of 330K.
These feed the EL84 pin 2 control grids.
These are in the feedback loop.
R207 reads 1.465K which is close to 1.5K on the schematic.
R252 reads 1.466K instead of 56K on the schematic. This is the big outlier. Could this be a problem?
R207 and 252 are in series on either side and intersect the line from the Presence pot to the V5B pin 7 grid.
Can I change something somewhere to make the amp run a little cooler without messing up the sound?
Also the amp is noisy and they say it is caused by the C6 47pF cap and R104 3.3M in parallel at the input to the grid of V2A which is the first stage of the clean channel.
Can this be modified to quiet the amp down? Is there anything else that would help?
Thanks for any response.