ProtoDAC TDA1387 X8 project

[hifinet]

Lately, I am building a subminiature 6N16B tube output as the output stage of the TDA1387. 

As per circuit diagram attached, I use the same power supply (B+180V as opposed to 200V) as before in Lampizator and Audio Note tube output. No capacitor to the input grid and 56 ohm resistor for I/V. 

This time something funny happened. Static noise when MoOde was not playing any song. When music started, it was sort of broken with noise. It felt like the tubes were not totally turned on (I may be wrong). After I powered it off and then on again, no output. I took out the 1387x8 DAC chip and inserted it into my original PCB (original design, no output stage added), no sound either. Looked like the DAC chip was faulty.

I just order 4 more pieces of these 1387x8 chip but I need to find out why this happened before I plug in any chip into this 6N16B board.

I have checked the tube pinout and connections a few times as the 6N16B pinout is rather unusual. I couldn't find any mistake.

My underlying assumption is since this is SRPP configuration, it can be used for current output DAC. Just take out the input grid capacitor and adjust the I/V resistor value. Even if this is meant for only voltage output DAC, it shouldn't cause damage to the 1387.

Any idea?

I would check both the TDA1387 and the 6N16B independently first. Use some 430R I/V resistors and listen to the TDA1387 to be sure there isn't any noise. By the way, there are more sellers of TDA1387 modules now, and the prices are much lower (35% lower).

Then test the 6N16B circuit and measure DC voltages at the plates, cathodes and grids at idle to be sure everything is functioning properly. If it all looks good, put the two together.