by stewdan Mon Sep 24, 2012 8:41 pm
Hi Harold --
I have Mark IIIs with Roy's VTA Lo Gain (12AU7) Boards mated with the SDS Cap Board and I also have Mark IIIs with Roy's VTA Octal (6SN7) Boards, also mated with the SDS Cap Board.
There was Forum Post back in March 2012, with the title "octal option??". Use the Forum's Seach Engine to scan for "octal option"
Take a look at the 2nd page of the Post (actually, Post #24) where Roy posted a wiring diagram which is valid for the Octal and 12AU7/12AT7 versions of the Mark III VTA Board. <<<======= INVALUABLE!!!
*********************************************************
The wiring of the SDS Cap Board to a Mark III with the VTA Board is as follows:
Connection points to the cap board are silk screened on the board for the "4 sections" that basically parrot the Dynaco Quad Cap. I used what Bob suggested and kept the GZ34 Rectifier Tube, so no diodes went to the Cap Board.
(1) connect the Red/Black wire from the Mark3 Bias line to the BIAS Eyelet of the VTA driver board.
(2) connect Section 1 of the Cap Board to pin #8 of the GZ34 and one side of the choke.
(3) connect Section 2 of the Cap Board to the other side of the choke and the red tap wire from the output transformer.
(4) connect Section 3 of the Cap Board to one end of a resistor, 2200 ohm 2 watt? And run a jumper wire from Section 3 back to Section 2.
(5 connect Section 4 of the Cap Board to the other end of the resistor, and run a wire from section 4 to the B+ eyelet of the Mark 3 VTA board.
*****************************************************************
So, between sections 2 and 3 of the Cap Board you run a jumper wire
And between sections 3 and 4 you run a 2200 ohm 2Watt resistor.
*******************************************************************
The Stock Mark III had 2 wires coming from the Stock Quad Cap to the Dynaco PCB --- solder points 5 and 6.
The VTA board only has 1 wire coming to the PCB from the Quad Cap, hence the jumpered sections of the Cap Board.
*********************************************************************
Hope this info helps. If you have questions, just ask.
Stew