Gents,
So I finished wiring up my ST70 clone, grabbed some cheap speakers, and gave it a go. First started it up w/o rectification, and got -48v @ J6 and J21...Good ! So then I plug in my 5AR4's.......
Oscillation Yellow_Light_Colorz_PDT_21
I immediately shut down and look back over things. I have the 16 ohm lead from the output transformers wired directly into J12 and J13. I have a wire running from each of the NEG binding posts back to my star ground.
The amp uses Edcor 4.2k OPT's, and the Triode PA060S Power Transformers. I have wired in 2 5AR4's in parallel, and also added a UL/Triode mode switch (amp isn't happy in either setting)
I triple checked the wiring on the sockets:
Pin1 - Tied to Pin 8
Pin 2 - AC heat
Pin 3 - Plate lead from OPT
Pin 4 - Screen
Pin 5 - Grid Resistor
Pin 6 - Input from board, tied to Grid Resistor
Pin 7 - AC heat
Pin 8 - 10 ohm resistor to ground
On the board:
J22 - Rear right KT88
J23 - Front right KT88
J1 - rear left KT88
J2 - Front left KT88
J9 - To Star Ground
J4/J5 - Left AC heat
J15/J16 - Right AC heat
J6/J21 - Bias wipers
J7 - Left Input +
J8 - Left Input -
J17 - Right Input +
J10 Right Input -
J19/J20 - To SDS Board
When I checked Resistance on the PCB, the weird reading I got was like 990k ohm on Pins 2 of V2 and V3. Pin 2 of V1 read OK 475k ohms. Also on J1/J2/J22/J23 I wasn't getting the 1.2M value shown in the manual, but rather 127k for all four. Beyond that, everything else is by the book so to speak.
Maybe I hooked up the SDS board wrong ? I don't think so though...My connections are:
Pin 8 of the rectifier goes into the B+ trace of the board. Where it says "RCATH-Inductor" I have a line out going to two Hammond 159V's in series. The next "INDUCTOR 2 - OUT" I have the line coming in from the Hammonds, and the two B+ lines going to the OPT's. EYE 19 and EYE 20 go to the respective ports on the PCB
Here are some photos - I know it is hard; but if anything JUMPS out at you - please lemme know.
For Reference:
Thanks for any help,
Steve
PS - I would like to be able to check voltages, etc - but I am afraid to while the amp isn't stable...