It might be safer to make the SDC cables have the transformer box permanently on the cable so it can't be omitted (signal to the transformer is high impedance and so the transformer to psu cable needs to be short). Depends if you can store the cable with the mic.
As this is a safety concern I am not willing to say how I wired mine (and I don't remember), but I didn't like the risk associated with the default pinouts on the Royer Schematics with an external transformer box.
The LDC PSU is
5 +6V
4 +93V-100V
3 GND
2 Sig (-?)
1 Sig (+?)
The SDC PSU is
5 +6V
4 GND
3 GND
2 +95V
1 +40V biased Sig out.
So the problem is, with the standard PSU pinouts:
If you plug the SDC into the LDC PSU, it will connect the heaters to +6V and the HT which probably is bad for your tube depending upon what current the PSU can muster. It will connect the anode to one signal line and the cathode to the other.I don't know if that is dangerous or not. The shield should also be tied to ground so you have some redundancy, and I don't know what the risks are of the 6V line going to 95V if the heater burns out it depends upon how the 6V traces run.
If you plug the LDC into the SDC PSU, it will connect HT (95 Volts) into the signal line via the transformer and to ground through a 37K resistor and through the 4.6K coil of the trafo (DC 20ma) which is not good for that little coil. Under the original Royer design the transformer in the SDC PSU would protect the mic pre, but if that coil is omitted then the mic pre could see high or very high voltage depending upon what burns out first which could fry things and depending upon the preamp could put lethal voltages where they should not be. So I felt I either needed to make it so I couldn't omit the transformer, or make the "wrong PSU" error just blow fuses. I chose the latter and changed the pinout.
I used the LDC pinout on the PSU's, and adjusted the wiring from the Mic to the little box.
As this is a safety concern I am not willing to say how I wired mine (and I don't remember), but I didn't like the risk associated with the default pinouts on the Royer Schematics with an external transformer box.
The LDC PSU is
5 +6V
4 +93V-100V
3 GND
2 Sig (-?)
1 Sig (+?)
The SDC PSU is
5 +6V
4 GND
3 GND
2 +95V
1 +40V biased Sig out.
So the problem is, with the standard PSU pinouts:
If you plug the SDC into the LDC PSU, it will connect the heaters to +6V and the HT which probably is bad for your tube depending upon what current the PSU can muster. It will connect the anode to one signal line and the cathode to the other.I don't know if that is dangerous or not. The shield should also be tied to ground so you have some redundancy, and I don't know what the risks are of the 6V line going to 95V if the heater burns out it depends upon how the 6V traces run.
If you plug the LDC into the SDC PSU, it will connect HT (95 Volts) into the signal line via the transformer and to ground through a 37K resistor and through the 4.6K coil of the trafo (DC 20ma) which is not good for that little coil. Under the original Royer design the transformer in the SDC PSU would protect the mic pre, but if that coil is omitted then the mic pre could see high or very high voltage depending upon what burns out first which could fry things and depending upon the preamp could put lethal voltages where they should not be. So I felt I either needed to make it so I couldn't omit the transformer, or make the "wrong PSU" error just blow fuses. I chose the latter and changed the pinout.
I used the LDC pinout on the PSU's, and adjusted the wiring from the Mic to the little box.
