mk IIB and fetron

[thecek]

hi everyone,
looking around on the web I've found the wiki page of the mark series. In the mk II section it say "The IIA and IIB, and some late-model Mark I amps, used a JFET-based device called "fetron" in place of the input stage 12AX7 (V1), and included a switch for configuring the amp for either fetron or 12AX7 operation...."
But reading on forums and other sites, I've understand that not every mkII (A and B) were built with the fetron. In my mkIIB, for example, I haven't found this device.
So, is there someone who can explain the matter? Maybe the production was not so uniform during that time? Maybe my amp, and others without the fetron, have been modified?
I would like to know if my mkIIB is still original or not...

 

[lesterpaul]

I don't think they all had the switch...?I figure the mod has been applied to a buttload of these amps
I bought my Mk IIB after it was sent back for the C+ conversion( a lovely little beast,indeed!)
if you haven't already done so, search for the freaky "fetron"

 

[igfraso]

As far as I know, on May 20, 1980, Mesa discontinued the Fetron during the last months of production of the Mark II-A and issued a letter announcing it.

The first Mark II-B was produced in August 14, 1980 so I could only guess that any II-B with the Fetron is due to the customer requesting it to the factory.

In fact, when you were sending you Mark to Petaluma for service, Mesa was recommending and offering to remove the Fetron.

 

[thecek]

well, my mkIIB has the hole on the chassis for the fetron switch, but inside there's no trace of the fetron.
infact, according to what igfraso said, my amp is dated '81 and so is correct that there isn't any fetron.
another question, a little OT
hidden between the power tubes there are the two jack connector for the footswitch...
I've tried to plug in a cable but nothing happens.
My mkIIb is the version with geq but no reverb, someone told me that one is for the eq and the other is for the pre-amp signal (I don't really understand what it means) ... someone else said that one jack is for the eq while the other is for the gain boost.
Even the "volume pedal trick" don't works...
Unfortunately I'm from Italy, and so is really difficult (and expensive) to send the amp to mesa for a check...

 

[lesterpaul]

edit

 

[lesterpaul]

from the II B manual:
A Pre Amp
Out - Pwr Amp In jack is located on the bottom of the chassis and provides access to the junction
of the preamp and the output power amp. With it, another Boogie can be linked up (Slave Out of
the first amp to Pwr Amp In of the second), or it an allow you to use the Boogie as a preamp only.
A volume pedal can be plugged into this pre-amp/power amp junction jack using just one cable
and will operate like a pedal operated remote Master 1 control.
and..
Also located beneath the chassis is a stereo socket for the optional Dual Footswitch. This will be
wired to activate, when applicable, the Graphic EQ and Reverb. When an amplifier is built with
only Reverb or Graphic, a mono 1/4” guitar jack is mounted for use with our Single Footswitch
and Cable Set. If your amplifier is equipped with a cooling fan and you wish to turn it off for quiet
studio playing, then unplug the fan power cord where it plugs into the chassis on the extreme left
end.
hope that helps

 

[thecek]

mumble mumble, I had to do some test....