adapting S.E.X. 2.1 C4S to 2.0 ?

[Bill S]

 I bought a S.E.X 2.0 in spring 2011 and purchased the C4S upgrade for it at that time. I never got around to installing the C4S and last year when I wanted to do it I couldn't find it the C4S kit although I found the assembly manual for it. I then purchased a C4S for version 2.1 so I have the installation manuals for both. What I don't have is a assembly manual for a S.E.X 2.1 to look at it's circuit.  I've been looking at the information I have and it looks like I might be able to use the 2.1 C4S in my version 2.0 amp.

 Does any one know if this will work?

 The component parts lists for the C4S kits are almost the same, same LED's, same transistors, same resistors on the board(s). The 2.0 kit uses two pc boards, the 2.1 kit is consolidated onto one board but it appears the circuits are the same. The 2.0 kit has replacement 18K 1W power supply resistors which the 2.1 kit does not have.

 It appears that if I were to try to use the 2.1 board I would:
 -assemble the 2.1 board as per instructions
 -remove the 150k plate load resistors
 -replace the 18K power supply resistors
 -connect 0A and 0B to A5 and B5 respectively
 - connect bA and bB to 18U and 38U respectively
 -connect 1A and 1B to 16U and 36 U respectively

 Can anyone verify if this would work?

Thanks,  Bill
 

[Paul Birkeland]

The "I" and "O" designations are the same on each board.  "BB" and "BA" are the same as "G".

It will be a little awkward to have one PC board with the 2.0 layout, but it's workable.  The 18K resistor provides some protection from over voltage of the MJE5731A in the event of a shorted tube and is a nice idea, so use them if you have them.

[Bill S]

Thanks Paul. 
Another question though. In my original post I wrote of connecting both bA and bB on the C4s board to their respective terminals of 18U and 38U, both of which are grounds. If I build the 2.1 pc board as shown in it's instructions, the bA and bB on the board are connected with a black wire so it appears I would only need to connect bA to either 18U or 38U to ground the C4S circuit. Is that correct?

 I'm sure as soon as I do this I'll find my original 2.0 kit. I had major home renovations done that started just after I built my amp in spring 2011 and my electronics stuff got moved several times during the renovations.

  Bill

[Paul Birkeland]

You can do it either way.  Technically it is slightly better to not connect BA/BB together and to run separate ground wires in a SEX 2.0.