Mesa Boogie Mark II TR1009 Fetron?

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Dimebucker

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Does anyone know what would be case on this my amplifier, because bottom is 2-way switch where you can choose Fetron or 12ax7A. But i did get this amp and it was set to right, which i guess is Fetron spot but i did check that one tube slot which should be V1 Fetron socket? And someone has install there 12ax7a preamp-tube.

My question is now do i need to pull that 2-way switch to left if you look behind amplifer or leave it right like it was set? And how i can be sure or can it test somehow, if someone has remove that Fetron thingy and you can use just 12ax7a:s?

https://ibb.co/gMrRRvm
 
Since there is a 12AX7 installed, the switch should be flipped to the 12AX7 position, not the TR1009, as it is in your picture. So, flip it the other way.
 
MisterMojo said:
Since there is a 12AX7 installed, the switch should be flipped to the 12AX7 position, not the TR1009, as it is in your picture. So, flip it the other way.
Click to expand...

I would like to do that but thing is that if someone has done something on this one, how i can check does that switch works like it should if i flip it other way around and someone has modded it there is risk do damage? Can someone give me some kind of pics guts inside of Mark II:s where is Fetron board, and how i can check does it even work or not?
 
Here is picture inside amplifier where you can see that 2-way switch, not sure if that helps you guys to check if someone has mod or remove that fetron option and that why he did use 12ax7 even switch were set to fetron picture link below does that tell anything?

https://ibb.co/XXS4PQn
 
Does anyone have some pictures for that bypass routing on that Fetron, or if you have pictures amplifers which has that Fetron circuit on it still would be nice to see how it looks inside of unit?

Also what could happening if you would have that Fetron circuit there, and you would use that Fetron mode and not 12ax7a mode put you would have there 12ax7 preamp-tube on socket? What things it could break/damaged, or should it sounds somehow weird or weak signal maybe?
 
Here is what my IIA with Fetron looked like, before Mike B removed it. Looks the same as your pic, to my eye.

https://imgur.com/MLZsSG9
 
MisterMojo said:
Here is what my IIA with Fetron looked like, before Mike B removed it. Looks the same as your pic, to my eye.

https://imgur.com/MLZsSG9
Click to expand...

Nice to see some pics ye it looks almost same i have just few different resistors there, could you get same photo but after fetron were bypassed on the board? And does that fetron has some kind of own board inside amplifier, and can you let me know what things they did on that your II-A exactly?
 
Also what could happening if i would let that switch to be Fetron position and not 12ax7 position, would it destroy or damage some components or should volume just go away or amp shut down what it could do?
 
Have you found the MKIIA Manual before?
https://www.manualslib.com/manual/564188/Mesa-Boogie-Mark-Iia.html

Fetron is mentioned on page 3. It says:
"switch to the right for Fetron, switch to the left for tube, viewed from the rear of the amplifier".

On page 2 of Maintenance & Repair section of the manual it says:
"Do not operate the amp with fetron installed and switch in 12AX7 position as damage to fetron will occur".

It doesn't mention the reverse scenario though. If it were problematic for the 12AX7 to be configured incorrectly you would think they would have also mentioned it.

There is an image here from Reverb.com of a Mark II that shows the text and switch direction info too:
https://images.reverb.com/image/upload/s--3B9gSAbV--/a_exif,c_limit,e_unsharp_mask:80,f_auto,fl_progressive,g_south,h_620,q_90,w_620/v1401469301/lq3g7m7nqkavxxw5euus.jpg
 
wildschwein said:
Have you found the MKIIA Manual before?
https://www.manualslib.com/manual/564188/Mesa-Boogie-Mark-Iia.html

Fetron is mentioned on page 3. It says:
"switch to the right for Fetron, switch to the left for tube, viewed from the rear of the amplifier".

On page 2 of Maintenance & Repair section of the manual it says:
"Do not operate the amp with fetron installed and switch in 12AX7 position as damage to fetron will occur".

It doesn't mention the reverse scenario though. If it were problematic for the 12AX7 to be configured incorrectly you would think they would have also mentioned it.

There is is an image here from Reverb.com of a Mark II that shows the text and switch direction info too:
https://images.reverb.com/image/upload/s--3B9gSAbV--/a_exif,c_limit,e_unsharp_mask:80,f_auto,fl_progressive,g_south,h_620,q_90,w_620/v1401469301/lq3g7m7nqkavxxw5euus.jpg
Click to expand...

Thanks for those links and info, i have seen that manual some time ago past.
 
From what I remember from mine; you won't hurt the 12AX7 with the switch either way. That switch reduces the voltage, so if you have a tube in, you won't get full performance from the 12AX7. BUT, if you put the Fetron TR1009 in, and have it in the 12AX7 position, it will burn out that Fetron. Too much voltage.

Personally, I never liked the sound of the Fetron, and it's in a drawer somewhere.
 

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